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Dr. Kaan Yücel yeditepeanatomyfhs122.wordpress.com/category/nervous-system

INTRODUCTION TO NERVOUS SYSTEMThe nervous system comprises the central nervous system (CNS) and the peripheral nervous system

(PNS). The CNS is surrounded and protected by the skull (neurocranium) and vertebral column and consists of the brain and the spinal cord. The PNS exists primarily outside these bony structures.

The entire nervous system is composed of neurons, which are characterized by their ability to conduct information in the form of impulses (action potentials), and their supporting cells plus some connective tissue. A neuron has a cell body (perikaryon) with its nucleus and organelles that support the functions of the cell and its processes. Dendrites are the numerous short processes that carry an action potential toward the neuron’s cell body, and an axon is the long process that carries the action potential away from the cell body. Many axons are ensheathed with a substance called myelin, which acts as an insulator. Myelinated axons transmit impulses much faster than nonmyelinated axons.

One neuron communicates with other neurons or glands or muscle cells across a junction between cells called a synapse. Typically, communication is transmitted across a synapse by means of specific neurotransmitters, such as acetylcholine, epinephrine, and norepinephrine, but in some cases in the CNS by means of electric current passing from cell to cell.

The central nervous system consists of the brain and spinal cord, and the peripheral nervous system consists of the sensory and motor nerves that are distributed throughout the body and that convey information to and from the brain (via 12 pairs of cranial nerves) and the spinal cord (via 31 pairs of spinal nerves). The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system.

The somatic nervous system is the part of the PNS that innervates the skin, joints, and skeletal muscles.

The autonomic nervous system (ANS) is the part of the PNS that innervates internal organs, blood vessels,and glands.

2. NEURONS & GLIAL CELLSInformation coming from peripheral receptors that sense the environment is analyzed by the brain

into components that give rise to perceptions, some of which are stored in memory. On the basis of this information, the brain gives commands for the proper action (motor, emotional, autonomic, cognitive, etc. responses). The brain does all this with nerve cells and the connections between them. Despite the simplicity of the basic units, the complexity of behavior –evident in our capability for perception, information storage, and action-, is achieved by the concerted signaling of an enormous number of neurons. The best estimate is that the human brain contains about 100 billion neurons. Although nerve cells can be classified into perhaps as many as 10,000 different types, they share many common features.

A key discovery in the organization of the brain is that nerve cells with basically similar properties are able to produce very different actions because of precise connections with each other and with sensory receptors and muscle.

Nerve cells differ from other cells in the body because of their ability to communicate rapidly with one another, sometimes over great distances and with great precision. The rapid and precise communication is made possible by two mechanisms- axonal conduction and synaptic transmission. Synaptic transmission can be electrical or chemical. At chemical synapses the pre-and post-synaptic elements are separated by a synaptic cleft.

A typical neuron has four morphologically defined regions: the cell body [also called the soma, consisting of the nucleus and perikaryon]; dendrites, axon and presynaptic terminals. Each of these regions has a distinct function in the generation of signals. Nerve cells differ most at the molecular level. The cell body is the metabolic center of the neuron. The cell body usually gives rise to two types of processes called the dendrites and the axon. A neuron usually has several dendrites; the branch out in tree-like fashion and serve as the main apparatus for receiving the input to the neuron from other nerve cells. Often the cell body is triangular or pyramidal in shape.

The cell body also gives rise to one axon, a tubular process with a diameter ranging that can ramify and extend up to 1 meter. The axon is the main conducting unit of the neuron; it is capable of conveying information great distances by propagating the signal and producing the transient electrical signal, called

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action potential. Large axons are surrounded by a fatty insulating sheath called myelin, which is essential for high-speed conduction of action potentials.

Near its end the axon divides into fine branches that have specialized swellings called presynaptic terminals; these are the transmitting elements of a neuron. By means of its terminals, one neuron transmits information about its activity to the receptor surfaces (for example dendrites) of other neurons. The point of contact is known as synapse. The neuron sending out the information, therefore is called the presynaptic neuron, the neuron receiving the information is called the postsynaptic neuron. The space separating the presynaptic from the postsynaptic cell is called the synaptic cleft. Most presynaptic neurons terminate near the postsynaptic neuron’s dendrites, but communication may occur with the cell body or, less often, with the initial segment or terminal portion of the axons.

Neuron types:On the basis of the number of processes that arise from the cell body, neurons are classified into

three large groups:1) Unipolar neurons: have one primary process that may give rise to many branches. One branch is

the axon and other branches serve as dendritic receiving structures. 2) Bipolar neurons: have an ovoid soma and two processes; a peripheral process or dendrite which

conveys information from the periphery, and a central process or axon, which carries information toward the CNS. Many bipolar cells are sensory.

3) Multipolar neurons: predominate in the vertebrate nervous system. These cells have a single axon and one or more dendritic branches that typically emerge from all parts of the cell body. The size and shape of cells vary. The larger dendritic tree of the Purkinje cell of the cerebellum receives approximately 150.000 contacts.

The neurons of the brain can be classified functionally into three major groups: afferent, motor, and interneurons. Afferent or sensory neurons carry information into the nervous system both for conscious perception and for motor coordination. Motor neurons carry commands to muscles and glands. Interneurons constitute by far the largest class and consist of all the remaining cells in the nervous system that are not specifically sensory or motor. Interneurons process information locally or convey information from one site within the nervous system to another.

Glial cellsNerve cell bodies and axons are surrounded by glial cells [Greek glia, “glue”]. There are between 10

and 50 times more glial cells than neurons in the CNS. Glial cells have other roles than processing information. Some of the functions of the glial cells are as follows:

1- They serve as supporting elements, providing firmness and structures to the brain. They also separate and occasionally insulate groups of neurons from each other.

2- Oligodendrocyte in the CNS forms myelin, the insulating sheath that covers most large axons. 3- Some glial cells remove debris after injury or neuronal death.4- Some glial cells take up and remove chemical transmitters released by neurons during synaptic

transmission.5- Some glial cells have nutritive functions for nerve cells. Glial cells are divided into two major classes: microglia and macroglia. Ependymal cells are also

considered as glial cells.TYPES OF NERVES

The PNS is anatomically and operationally continuous with the CNS. Its afferent (sensory) fibers convey neural impulses to the CNS from the sense organs (e.g., the eyes) and from sensory receptors in various parts of the body (e.g., in the skin). Its efferent (motor) fibers convey neural impulses from the CNS to effector organs (muscles and glands). Nerves are either cranial nerves or spinal nerves, or derivatives of them.

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SPINAL CORDThe spinal cord is a vital communication link between the brain and the peripheral nervous

system. Within the spinal cord, sensory nerves carry messages from the body to the brain for interpretation, and motor nerves relay messages from the brain to the effectors. The spinal cord is also the primary reflex centre, coordinating rapidly incoming and outgoing neural information.

The spinal cord is the major reflex center and conduction pathway between the body and brain. This cylindrical structure, slightly flattened anteriorly and posteriorly, is protected by the vertebrae, their associated ligaments and muscles, the spinal meninges, and the cerebrospinal fluid (CSF).

The spinal cord begins as a continuation of the medulla oblongata (commonly called the medulla), the caudal part of the brainstem In adults, the spinal cord is 42-45 cm long and extends from the foramen magnum in the occipital bone to the level of the L1 or L2 vertebra. However, its tapering inferior end, the conus medullaris, may terminate as high as T12 vertebra or as low as L3 vertebra. Thus the spinal cord occupies only the superior two thirds of the vertebral canal. In neonates, the spinal cord extends approximately to vertebra LIII, but can reach as low as vertebra LIV. In the young child, it is relatively longer and ends at the upper border of the third lumbar vertebra. The distal end of the cord (the conus medullaris) is cone shaped. A fine filament of connective tissue (the pial part of the filum terminale) continues inferiorly from the apex of the conus medullaris.

Although the spinal cord terminates at the level of first or second lumbar vertebra, the filum terminale and the spinal nerve roots from the lumbosacral part of the spinal cord that form the cauda equina continue inferiorly within the lumbar cistern containing CSF. This bundle of spinal nerve roots arising inferior to the L1 vertebra, known as the cauda equina (L. horse tail), descends past the termination of the spinal cord.

The spinal cord is not uniform in diameter along its length. It has two major swellings or enlargements in regions associated with the origin of spinal nerves that innervate the upper and lower limbs. A cervical enlargement occurs in the region associated with the origins of spinal nerves C5 to T1, which innervate the upper limbs (brachial plexus). A lumbosacral enlargement occurs in the region associated with the origins of spinal nerves L1 to S4, which innervate the lower limbs (lumbosacral plexus).

Inferiorly, the spinal cord tapers off into the conus medullaris, from the apex of which a prolongation of the pia mater, the filum terminale, descends to be attached to the back of the coccyx . The cord possesses in the midline anteriorly a deep longitudinal fissure, the anterior median fissure, and on the posterior surface a shallow furrow, the posterior median sulcus. Internally, the cord has a small central canal (containing CSF) surrounded by gray and white matter:

The gray matter is rich in nerve cell bodies, which form longitudinal columns along the cord, and in cross-section these columns form a characteristic H-shaped appearance in the central regions of the cord;The white matter surrounds the gray matter and is rich in nerve cell processes, which form large bundles or tracts that ascend and descend in the cord to other spinal cord levels or carry information to and from the brain.

The spinal cord is a long tubular structure that is divided into a peripheral white matter (composed of myelinated axons) and a central gray matter (cell bodies and their connecting fibers). When viewed in cross section, the gray matter has pairs of horn-like projections into the surrounding white matter. These horns are called ventral horns, dorsal horns, and lateral horns, but in three dimensions they represent columns that run the length of the spinal cord.

The ventral horns contain the cell bodies of motor neurons and their axons. A collection of neuronal cell bodies in the CNS is a nucleus. Axons of the ventral horn nuclei leave the spinal cord in bundles called ventral roots. These motor fibers innervate skeletal muscles.

The lateral (intermediolateral) horns contain the cell bodies for the sympathetic nervous system at spinal cord levels T1–L2 and for the parasympathetic nervous system at spinal cord levels S2–S4. The axons from these neurons also leave the spinal cord through the ventral root and will synapse in various peripheral ganglia. A collection of neuronal cell bodies in the PNS is a ganglion.

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Dr. Kaan Yücel yeditepeanatomyfhs122.wordpress.com/category/nervous-systemThe dorsal horns receive the sensory fibers originating in the peripheral nervous system. Sensory

fibers reach the dorsal horn by means of a bundle called the dorsal root. The central axons of the sensory neuron enter the dorsal horn of the gray matter. Some of these fibers will run in tracts (a bundle of fibers in

the CNS) of the white matter to reach other parts of the CNS. Other axons will synapse with intercalated neurons (interneurons), which in turn synapse with motor neurons in the ventral horn to form a reflex arc.

The arterial supply to the spinal cord comes from two sources. It consists of: longitudinally oriented vessels, arising superior to the cervical portion of the cord, which descend on the surface of the cord; and feeder arteries that enter the vertebral canal through the intervertebral foramina at every level; these feeder vessels, or segmental spinal arteries, arise predominantly from the vertebral and deep cervical arteries in

the neck, the posterior intercostal arteries in the thorax, and the lumbar arteries in the abdomen. After entering an intervertebral foramen, the segmental spinal arteries give rise to anterior and posterior radicular arteries. This occurs at every vertebral level.

The longitudinal vessels consist of: a single anterior spinal artery, which originates from the vertebral arteries- passes inferiorly, approximately parallel to the anterior median fissure, along the surface of the spinal cord; and two posterior spinal arteries, which also originate in the cranial cavity, usually arising directly from a terminal branch of each vertebral artery. The right and left posterior spinal arteries descend along the spinal cord, bracket the posterolateral sulcus.

Veins that drain the spinal cord form a number of longitudinal channels. These longitudinal channels drain into an extensive internal vertebral plexus in the extradural (epidural) space of the vertebral canal.

.Spinal NervesSpinal nerves initially arise from the spinal cord as rootlets; the rootlets converge to form two nerve

roots. An anterior (ventral) nerve root, consisting of motor (efferent) fibers passing from nerve cell bodies in the anterior horn of spinal cord gray matter to effector organs located peripherally.

A posterior (dorsal) nerve root, consisting of sensory (afferent) fibers from cell bodies in the spinal sensory or posterior (dorsal) root ganglion that extend peripherally to sensory endings and centrally to the posterior horn of spinal cord gray matter.

The posterior and anterior nerve roots unite, within or just proximal to the intervertebral foramen, to form a mixed (both motor and sensory) spinal nerve, which immediately divides into two rami (L., branches): a posterior (dorsal) ramus and an anterior (ventral) ramus. As branches of the mixed spinal nerve, the posterior and anterior rami carry both motor and sensory fibers, as do all their subsequent branches. The terms motor nerve and sensory nerve are almost always relative terms, referring to the majority of fiber types conveyed by that nerve. Nerves supplying muscles of the trunk or limbs (motor nerves) also contain about 40% sensory fibers, which convey pain and proprioceptive information. Conversely, cutaneous (sensory) nerves contain motor fibers, which serve sweat glands and the smooth muscle of blood vessels and hair follicles.

Posterior rami are distributed to the synovial joints of the vertebral column, deep muscles of the back, and the overlying skin. The remaining anterolateral body wall, including the limbs, is supplied by anterior rami. Posterior rami and the anterior rami of spinal nerves T2-T12 generally do not merge with the rami of adjacent spinal nerves to form plexuses.

Spinal (segmental) nerves exit the vertebral column (spine) through intervertebral foramina. Spinal nerves arise in bilateral pairs from a specific segment of the spinal cord. The 31 spinal cord segments and the 31 pairs of nerves arising from them are identified by a letter and number (e.g., “T4”) designating the region of the spinal cord and their superior-to-inferior order (C, cervical; T, thoracic; L, lumbar; S, sacral; Co, coccygeal). A spinal cord segment is the portion of the spinal cord that gives rise to a pair of spinal nerves. Thus, the spinal cord gives rise to 8 pairs of cervical nerves (C1–C8), 12 pairs of thoracic nerves (T1–T12), 5 pairs of lumbar nerves (L1–L5), 5 pairs of sacral nerves (S1–S5), and 1 pair of coccygeal nerves (Co1). The spinal cord segments are numbered in the same manner as these nerves.

The first cervical nerve (C1) emerges from the vertebral canal between the skull and vertebra CI. Therefore cervical nerves C2 to C7 also emerge from the vertebral canal above their respective vertebrae. Because there are only seven cervical vertebrae, C8 emerges between vertebrae CVII and TI. As a

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consequence, all remaining spinal nerves, beginning with T1, emerge from the vertebral canal below their respective vertebrae. Cervical spinal nerves (except C8) bear the same alphanumeric designation as the vertebrae forming the inferior margin of the IV foramina through which the nerve exits the vertebral canal. The more inferior spinal (T1 through Co1) nerves bear the same alphanumeric designation as the vertebrae

forming the superior margin of their exit. The first cervical nerves lack posterior roots in 50% of people, and the coccygeal nerve may be absent.

Although the dorsal root is essentially sensory and the ventral root is motor, the two roots come together within the bony intervertebral foramen to form a mixed spinal nerve (i.e., it contains both sensory and motor fibers). The spinal cord is defined as part of the CNS, but the ventral and dorsal roots are considered parts of the PNS. Outside the intervertebral foramen, the mixed nerve divides into a ventral ramus (from the Latin for “branch”) and a dorsal ramus.

The larger ventral ramus supplies the ventrolateral body wall and the limbs; the smaller dorsal ramus supplies the back. Since the ventral and dorsal rami are branches of the mixed nerve, they both carry sensory and motor fibers.

The term “peripheral nerve” such as sciatic nerve, ulnar nerve etc. should not be confused by the spinal nerve. Peripheral nerve is the last product of these somatic networks; somatic plexuses.

The anterior rami form plexuses (network). All major somatic plexuses (cervical, brachial, lumbar, and sacral) are formed by anterior rami (ramus=branch, rami=branches).

The peripheral nervous system contains two systems; one working voluntarily; somatic nervous system (soma, in ancient Greek, body), and one involuntarily, as it name implies, autonomic nervous system.

The unilateral area of skin innervated by the sensory fibers of a single spinal nerve is called a dermatome; the unilateral muscle mass receiving innervation from the fibers conveyed by a single spinal nerve is a myotome. Generally, at least two adjacent spinal nerves (or posterior roots) must be interrupted to produce a discernible area of numbness.

As they emerge from the intervertebral foramina, spinal nerves are divided into two rami Posterior (primary) rami of spinal nerves supply nerve fibers to the synovial joints of the vertebral column, deep muscles of the back, and the overlying skin in a segmental pattern. As a general rule, the posterior rami remain separate from each other (do not merge to form major somatic nerve plexuses). Anterior (primary) rami of spinal nerves supply nerve fibers to the much larger remaining area, consisting of the anterior and lateral regions of the trunk and the upper and lower limbs. The anterior rami that are distributed exclusively to the trunk generally remain separate from each other, also innervating muscles and skin in a segmental pattern. However, primarily in relationship to the innervation of the limbs, the majority of anterior rami merge with one or more adjacent anterior rami, forming the major somatic nerve plexuses (networks) in which their fibers intermingle and from which a new set of multisegmental peripheral nerves emerges. The anterior rami of spinal nerves participating in plexus formation contribute fibers to multiple peripheral nerves arising from the plexus; conversely, most peripheral nerves arising from the plexus contain fibers from multiple spinal nerves.

Spinal meningesThe spinal dura mater is the outermost meningeal membrane and is separated from the bones forming

the vertebral canal by an extradural space. Superiorly, it is continuous with the inner meningeal layer of cranial dura mater at the foramen magnum of the skull. Inferiorly, the dural sac dramatically narrows at the level of the lower border of vertebra SII and forms an investing sheath for the pial part of the filum terminale of the spinal cord. This terminal cord-like extension of dura mater (the dural part of the filum terminale) attaches to the posterior surface of the vertebral bodies of the coccyx.

The arachnoid mater is a thin delicate membrane against, but not adherent to, the deep surface of the dura mater. It is separated from the pia mater by the subarachnoid space. The arachnoid mater ends at the level of vertebra SII.

The subarachnoid space between the arachnoid and pia mater contains CSF (Cerebrospinal fluid-Beyin-omurilik sıvısı-BOS). The subarachnoid space around the spinal cord is continuous at the foramen magnum with the subarachnoid space surrounding the brain.

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Dr. Kaan Yücel yeditepeanatomyfhs122.wordpress.com/category/nervous-systemThe spinal pia mater is a vascular membrane that firmly adheres to the surface of the spinal cord.

INTRODUCTION TO THE BRAINThe brain (encephalon; Greek, within the head) is divided into three major divisions. These are, in

ascending order from the spinal cord;1) Hindbrain (Rhombencephalon)I. Medulla oblongataII. PonsIII. CerebellumPons and cerebellum are called as metencephalon.2) Midbrain (Mesencephalon)3) Forebrain (Prosencephalon)I. Telencephalon (Cerebrum)II. Diencephalon (between brain)The brainstem (a collective term for the medulla oblongata, pons, and midbrain) is that part of the

brain that remains after the cerebral hemispheres and cerebellum are removed.1. Telencephalon (Cerebrum): Telencephalon by far forms the largest region of the brain. They

consist of the cerebral hemispheres, basal ganglia and ventricles. The basal ganglia participate in regulating motor performance.

2. Diencephalon: Diencephalon or between-brain is so called because it lies between the cerebral hemispheres and the midbrain. The main structures of the diencephalon are the thalamus and hypothalamus. The thalamus processes most of the information reaching the cerebral cortex from the rest of the central nervous system. Hypothalamus regulates autonomic, endocrine, and visceral function.

3. Mesencephalon (Midbrain): is the smallest brain stem component and lies anterior to pons. Several regions of the midbrain play a dominant role in the direct control of eye movements, whereas others are involved in motor control of skeletal muscles. The midbrain is also involved with the coordination of visual and auditory reflexes.

4. Metencephalon [Pons+Cerebellum] Pons (Latin, bridge), which lies above the medulla, conveys information about movement from the

cerebral hemisphere to the cerebellum. Cerebellum, lies behind the pons and is connected to the brain stem by several major fiber tracts

called peduncles. The cerebellum modulates the force and range of movement and is involved in learning of motor skills.

5. Medulla oblongata (medulla): which lies directly above the spinal cord, includes several centers responsible for such vital autonomic functions as digestion, breathing, and the control of heart rate.

BRAINSTEMThe brainstem is the oldest part of the CNS. The brainstem is made up of the medulla oblongata, the pons, and the midbrain and occupies the posterior cranial fossa of the skull. It is stalklike in shape and connects the narrow spinal cord with the expanded forebrain. The brain stem contains 10 cranial nerves, and most of the motor and sensory systems pass through this important region. It is a relatively small region (approximately 7 cm long) that links the forebrain (i.e., cerebral cortex) and the spinal cord and all messages going between the two areas must go through the brain stem.The brainstem has three broad functions: (1) it serves as a conduit for the ascending tracts and descending tracts connecting the spinal cord to the different parts of the higher centers in the forebrain; (2) it contains important reflex centers associated with the control of respiration and the cardiovascular system and with the control of consciousness; and (3) it contains the important nuclei of cranial nerves III through XII.

Midbrain [Mesencephalon]6


The midbrain measures about 0.8 inch (2 cm) in length and connects the pons and cerebellum with the forebrain. The cerebral hemispheres are connected to the brainstem by two large fiber tracts , the cerebral peduncles. The narrow cavity of the midbrain is the cerebral aqueduct, which connects the third and fourth ventricles.The dorsal aspect of the midbrain is known as the tectum (L., roof] and incorporates the paired superior and inferior colluculi (singular, colliculus). The superior and inferior colliculi are also known as corpora quadrigemina. These are rounded eminences that are divided into superior and inferior pairs by a vertical and a transverse groove. The superior colliculi are centers for visual reflexes, and the inferior colliculi are lower auditory centers. The region of the mesencephalon below the cerebral aqueduct is known as the midbrain (mesencephalic) tegmentum (L., cover). The midbrain comprises two lateral halves, called the cerebral peduncles; each of these is divided into an anterior part, the crus cerebri, and a posterior part, the tegmentum, by a pigmented band of gray matter, the substantia nigra. The substantia nigra is a large motor nucleus situated between the tegmentum, and the crus cerebri and is found throughout the midbrain. The substantia nigra is concerned with muscle tone and is connected to the cerebral cortex, spinal cord, hypothalamus, and basal nuclei.The crus cerebri contains important descending tracts and is separated from the tegmentum by the substantia nigra. These descending tracts connect the cerebral cortex to the anterior gray column cells of the spinal cord, the cranial nerve nuclei, the pons, and the cerebellum.

PonsThe pons is anterior to the cerebellum and connects the medulla oblongata to the midbrain. It is about 1 inch (2.5 cm) long and owes its name to the appearance presented on the anterior surface, which is that of a bridge connecting the right and left cerebellar hemispheres.The anterior surface is convex from side to side and shows many transverse fibers that converge on each side to form the middle cerebellar peduncle. Pons has a convex anterior surface marked by transversely running fibers which laterally forms a bundle called middle cerebellar peduncle.Main Features- The trigeminal nerve emerges from the anterior surface at its junction with middle cerebellar peduncle.- Presents a basilar sulcus in the midline which lodges basilar artery- In the groove between Pons and the medulla oblongata, there emerge, from medial to lateral, abducent, facial and vestibulocochlear nerves.Posterior surface of the pons is limited laterally by superior cerebellar peduncle and forms the upper part of the floor of the 4th ventricle.Main Features:- The floor is divided into symmetrical halves by a median sulcus.- Lateral to this sulcus is an elongated elevation, the medial eminence, which is bounded laterally by a sulcus limitans.- Inferior end of medial eminence is slightly expanded to form facial colliculus, which is produced by facial nerve- The upper end of sulcus limitans presents a bluish-gray coloration and the area is called substantia ferruginosa.- Area vestibule lies lateral to sulcus limitansParts of the Pons· a posterior part, the tegmentum, and· an anterior basilar part

Medulla OblongataThe medulla oblongata is situated in the posterior cranial fossa, lying beneath the tentorium cerebelli

and above the foramen magnum. It is related anteriorly to the basal portion of the occipital bone and the upper part of the odontoid process of the axis and posteriorly to the cerebellum.

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The medulla oblongata not only contains many cranial nerve nuclei that are concerned with vital functions (e.g., regulation of heart rate and respiration), but it also serves as a conduit for the passage of ascending and descending tracts connecting the spinal cord to the higher centers of the nervous system.

The medulla oblongata is conical in shape. Its broad part joins the pons above and narrow part becomes continuous with the spinal cord. The junction between medulla and spinal cord coincides with the level of the upper border of atlas (first cervical vertebra).Its length is about 3 cm and its width is about 2cm at its upper end.It is divided into1. A lower closed part with central canal and2. An upper open part posteriorly which is related to the lower part of the 4th ventricleFeatures on the anterior surface of Medulla OblongataAnterior median fissure, is an upward continuation of similar fissure present on the spinal cordAnterolateral sulcus, on each side, is in line with the ventral roots of spinal cord- Gives attachment to the rootlets of the hypoglossal nervePyramid is an elevation on each side of the midline between anterior median fissure and anterolateral sulcus.- Composed of bundles of nerve fibers of corticospinal tract that descends from the cerebral cortex to the spinal cord- Tapers inferiorly where the majority of fibers cross over to the opposite side, obliterating the medulla. These crossing fibers constitute the decussation of the pyramid.

Olive is a prominent, elongated oval swelling that lies in the upper part of medulla posterolateral to the pyramid separated by anterolateral sulcus.The elevation is produced by the underlying inferior olivary nucleus.Features on posterior surface of the medulla oblongataPosterior median sulcus is upward continuation of the similar fissure on the spinal cord.Posterolateral sulcus lies in line with the dorsal roots of spinal nerves.- Gives attachment to the rootlets of 9th, 10th and 11th cranial nerves.Between the posterior median sulcus and posterolateral sulcus, the medulla contains tracts (asccending) that enter it from the posterior funiculus of the spinal cord.- Fasciculus gracilis lies medially and fasciculus cuneatus lies laterally- Both fasciculi end in rounded elevations called gracile tubercle (nucleus gracilis) and cuneate tubercle (nucleus cuneatus) respectively.Just above these tubercles, medulla is occupied by a triangular fossa which forms the lower part of the 4th ventricle. This fossa is bounded on each side by inferior cerebellar peduncle which connect the medulla to cerebellum.Features on the posterior part of the medulla that forms the floor of the 4th ventricle:Presents median sulcus, on each side of which there is a longitudinal elevation called the median eminence (continuous above in the pontine part of the floor of 4th ventricle). The eminence is bounded laterally by sulcus limitans.The sulcus limitans is marked by a depression called inferior fovea. The part of the medulla below fovea presents hypoglossal triangle medially and vagal triangle laterally.The inferior angle where the lateral margins of the floor meet is called obex.

CRANIAL NERVESThe 12 pairs of cranial nerves are part of the peripheral nervous system (PNS) and pass through

foramina or fissures in the cranial cavity. All nerves except one, the accessory nerve [XI], originate from the brain. In addition to having similar somatic and visceral components as spinal nerves, some cranial nerves also contain special sensory (such as hearing, seeing, smelling, balancing, and tasting). The special sensory components are associated with.

Nuclei of 12 cranial nerves10 of them in the brainstemMidbrain Of the IV & IIIPons Of the other 4 - VIII,VII,VI,V

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Dr. Kaan Yücel yeditepeanatomyfhs122.wordpress.com/category/nervous-systemMedulla Of the last 4 - XII,XI,X, IXI Olfactory Purely sensory TelencephalonSmellingII Optic Sensory Retinal ganglion cellsSeeing III Oculomotor Mainly motor MidbrainEye movements & pupillary reflex IV Trochlear Motor MidbrainIntorts the eyeball. V Trigeminal Both sensory and motor PonsReceives sensation from the face and innervates the muscles of masticationVI Abducens Mainly motor PonsAbducts the eye.VII Facial Both sensory and motor Pons Provides motor innervation to the muscles of facial expression. Also receives the special sense of

taste from the anterior 2/3 of the tongue and provides secretomotor innervation to the salivary glands (except parotid) and the lacrimal gland.

VIII Vestibulocochlear Mostly sensory PonsHearing and balanceIX Glossopharyngeal Both sensory and motor MedullaReceives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the

parotid gland, and provides motor innervation to the stylopharyngeus. Some sensation is also relayed to the brain from the palatine tonsils.

X Vagus Both sensory and motor MedullaSupplies branchiomotor innervation to most laryngeal and pharyngeal muscles (except the

stylopharyngeus, which is innervated by the glossopharyngeal). Also provides parasympathetic fibers to nearly all thoracic and abdominal viscera till the proximal two-thirds of the transverse colon. Receives the special sense of taste from the epiglottis. A major function: controls muscles for voice and resonance and the soft palate.

XI Accessory (often separated into the cranial accessory and spinal accessory nerves)MedullaMainly motor Cranial and Spinal RootsControls the sternocleidomastoid and trapezius muscles, and overlaps with functions of the vagus

nerve (CN X). Symptoms of damage: inability to shrug, weak head movement. XII Hypoglossal mainly motor MedullaProvides motor innervation to the muscles of the tongue (except for the palatoglossus, which is

innervated by the vagus nerve) and other glossal muscles. Important for swallowing (bolus formation) and speech articulation.

Reticular formationThe reticular formation (L. reticulum, “little net”) consists of various distinct populations of cells embed

in a network of cell processes occupying the central core of the brainstem. From an evolutionary perspective, the reticular formation is phylogenetically an ancient neural complex that is closely associated with two other ancient neural systems, the olfactory system which mediates the visceral sense of smell, and the limbic system which functions in the visceral and behavioral responses to emotions. The reticular formation consists of an intricate mixture of neuronal cell bodies and fascicles of axons running in small bundles, which are oriented in many different directions. Thus, as its name suggest, it is like a network extending from the spinal cord through the medulla, the pons, the midbrain, the subthalamus, hypothalamus and the thalamus.The reticular formation and the olfactory and limbic systems are interrelated as a result of their participation in visceral functions and behavioral responses. The reticular formation is continually informed of activity

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occurring in almost all areas of the nervous system and responds by influencing the following: skeletal muscle motor activity; somatic and visceral sensation; autonomic nervous system; endocrine functions; biological rhythms, via reciprocal connections to the hypothalamus, and the level of consciousness.More than 100 nuclei scattered throughout the tegmentum of the midbrain, pons and medulla have been identified as being part of the brainstem reticular formation. Most of the nuclei of the reticular formation are not clearly as defined as are other nuclei of the CNS. Although the nuclei of the reticular formation have a number of diverse functions, they are classified according to the following four general functions:1- The regulation of the level of consciousness, and ultimately cortical alertness2- The control of somatic motor movements 3- The regulation of visceral motor or autonomic functions 4- The control of sensory information

Autonomic Nervous SystemThe autonomic nervous system is distributed throughout the central and peripheral nervous systems. It is

divided into two parts, the sympathetic and the parasympathetic and, consists of both afferent and efferent fibers. This division between sympathetic and parasympathetic is made on the basis of anatomical differences, differences in the neurotransmitters, and differences in the physiologic effects.The autonomic nervous system and the endocrine system control the internal environment of the body. It is the autonomic nervous system that provides a fine discrete control over the functions of many organs and tissues, including heart muscle, smooth muscle, and the exocrine glands.The autonomic nervous system functions for the most part at the subconscious level. We are not aware, for example, that our pupils are dilating or that our arteries are constricting. The system should not be regarded as an isolated portion of the nervous system, for it is known that it can play a role with somatic activity in expressing emotion and that certain autonomic activities, such as micturition, can be brought under voluntary control. The various activities of the autonomic and endocrine systems are integrated within the hypothalamus.The sympathetic part of the autonomic system has the efferent fibers originating from the spinal cord. The function of the sympathetic system is to prepare the body for an emergency. The heart rate is increased, arterioles of the skin and intestine are constricted, arterioles of skeletal muscle are dilated, and the blood pressure is raised. There is a redistribution of blood; thus, it leaves the skin and gastrointestinal tract and passes to the brain, heart, and skeletal muscle. In addition, the sympathetic nerves dilate the pupils; inhibit smooth muscle of the bronchi, intestine, and bladder wall; and close the sphincters. The hair is made to stand on end, and sweating occurs. The activities of the parasympathetic part of the autonomic system are directed toward conserving and restoring energy. The heart rate is slowed, pupils are constricted, peristalsis and glandular activity is increased, sphincters are opened, and the bladder wall is contracted.The connector nerve cells of the parasympathetic part of the autonomic nervous system are located in the brainstem and the sacral segments of the spinal cord.Parasympathetic System in the Brainstem Edinger-Westfall nucleus in the midbrain (mediates the diameter of the pupil in response to light) Superior and inferior salivatory nuclei in the pons and medulla (mediate salivary secretion and the

production of tears) Dorsal motor nucleus of the vagus nerve in the medulla. The parasympathetic system controls the motor

responses of the heart, lungs, and gut elicited by the vagus nerve (e.g., slowing of the heart rate and constriction of the bronchioles).

The sympathetic and parasympathetic components of the autonomic system cooperate in maintaining the stability of the internal environment. The sympathetic part prepares and mobilizes the body in an emergency, when there is sudden severe exercise, fear, or rage.The parasympathetic part aims at conserving and storing energy, for example, in the promotion of digestion and the absorption of food by increasing the secretions of the glands of the gastrointestinal tract and stimulating peristalsis. The sympathetic and parasympathetic parts of the autonomic system usually have antagonistic control over a viscus. For example, the sympathetic activity will increase the heart rate, whereas the parasympathetic

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activity will slow the heart rate. The sympathetic activity will make the bronchial smooth muscle relax, but the muscle is contracted by parasympathetic activity.

CEREBELLUMThe cerebellum (L. “little brain”) is the largest part of the hindbrain and lies posterior to the fourth

ventricle, the pons, and the medulla oblongata. The cerebellum is situated in the posterior cranial fossa and is covered superiorly by the tentorium cerebelli. It is made up of two lateral cerebellar hemispheres and a median vermis (L. “worm”). The surface of the cerebellum displays slender and parallel elevations (ridges) known as folia and depressions (grooves) known as sulci that facilitate a great increase in the surface area of the cerebellar cortex.

Though apparently smaller than the cerebral cortex, the cerebellum contains ~2X as many neurons as the cerebral cortex. Its function is to make our movements as fast, accurate, smooth, and consistent as possible. Cerebellar damage does not cause paralysis but renders movements slow, inaccurate, inconsistent, and jerky. Though the cerebellum sends very few fibers to the spinal cord it exerts a powerful influence on movements via projections, either direct or via one relay neuron, to the structures from which all four major descending motor tracks originate.

The cerebellum is connected to the dorsal aspect of the brainstem by three pairs of prominent fiber bundles, the superior, middle, and inferior cerebellar peduncles. On its ventral surface, near the middle cerebellar peduncle, a small, bulb-like region of each cerebellar hemisphere, known as the flocculus, is connected to a region of the vermis known as the nodulus. The effect of this fissuring is to give the cerebellum in section the appearance of a many branched tree which is called as arbor vitae; the tree of life.

The cerebellum is somewhat ovoid in shape and constricted in its median part. The cerebellum has traditionally been recognized as having three anterior-posterior divisions: the anterior lobe (lobules I – V) is separated from the posterior lobe by the primary fissure, and the posteriorlobe (lobules VI – IX) is separated from the flocculonodular lobe (lobule X) by the posterolateral fissure (posterior fissure or uvulonodular fissure). A deep horizontal fissure that is found along the margin of the cerebellum separates the superior from the inferior surfaces.The anterior lobe receives its input primarily from the spinal cord and is referred to as the paleocerebellumThe posterior lobe receives its input primarily from the cerebral cortex via relay neurons in the pontine nuclei and is called the neocerebellum. The flocculonodular lobe receives most of its input from the vestibular system and is called the vestibulocerebellum.

The cerebellum plays a very important role in the control of posture and voluntary movements. It unconsciously influences the smooth contraction of voluntary muscles and carefully coordinates their actions, together with the relaxation of their antagonists. Each cerebellar hemisphere controls muscular movements on the same side of the body and that the cerebellum has no direct pathway to the lower motor neurons but exerts its control via the cerebral cortex and the brainstem.

The cerebellum is composed of an outer covering of gray matter called the cortex and inner white matter. Embedded in the white matter of each hemisphere are three masses of gray matter forming the intracerebellar nuclei (deep cerebellar nuclei).

The human cerebellum contains more than 100 billion neurons, a number that represents about 80% of the total number of neurons in the brain. Unlike the cerebral cortex, the cortex of the cerebellum has uniform anatomical structure, suggesting that there may be a similar mode of operation for all its possible functions. The cortex of the cerebellum is deeply folded. If one looks at the human cerebral cortex,one can see about one third of it; two thirds is buried on the banks and depths of the fissures. For the cerebellar cortex, one would see only about one tenth; 90% is buried within the fissures.

The output from the cortex is mainly to the intracerebellar nuclei, which are buried within the white matter of the cerebellum. The white matter consists of fibers coming into the cerebellum and the axons of the output neurons of the cerebellar cortex, Purkinje cells, coursing to terminate in the cerebellar nuclei.

There are four nuclei on each side. Most laterally is the dentate or lateral nucleus. Most medially is the fastigial or medial nucleus. Between the lateral and medial nuclei are the intermediate, or interpositus nuclei, the globose (more lateral) and emboliform (more medial).

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Dr. Kaan Yücel yeditepeanatomyfhs122.wordpress.com/category/nervous-systemThirty million Purkinje cells are the only neurons whose axons carry information from the cortex to

the nuclei. Purkinje cell axons run through the white matter to terminate in the cerebellar nuclei. All output from the cerebellar cortex leaves the cortex via Purkinje cell axons. Climbing fibers terminate directly on the dendrites of ~10 Purkinje cells. An action potential in a climbing fiber always causes an action potential in the Purkinje cells that it contacts. Thus a mossy fiber has a small effect on many Purkinje cells, whereas climbing fibers have a large effect on a small number of Purkinje cells.

Cerebellar PedunclesThe cerebellum is linked to other parts of the central nervous system by numerous efferent and afferent fibers that are grouped together on each side into three large bundles, or peduncles. The superior cerebellar peduncles connect the cerebellum to the midbrain, the middle cerebellar peduncles connect the cerebellum to the pons, and the inferior cerebellar peduncles connect the cerebellum to the medulla oblongata.

Functions of the cerebellumCerebellum makes an important contribution to the control of voluntary movement and movement coordination, as well as control of balance, gait, and posture. Functions- 3 major functional roles1. Coordination of Movement-the cerebellum controls the timing and pattern of muscle activation duringmovement.2. Maintenance of Equilibrium (in conjunction with the vestibular system)3. Regulation of Muscle Tone-modulates spinal cord and brain stem mechanisms involved in posturalcontrol.

There is also strong evidence for a cerebellar role in cognition (memory, attention, language and executive functions), emotions, and anxiety.

DIENCEPHALONThe diencephalon is located at the dorsal end of the brain stem surrounded by the internal capsule

laterally and the lateral ventricles and corpus callosum superiorly. It is divided into symmetrical halves separated by the narrow third ventricle but connected by the massa intermedia.As you will see the structures of the diencephalon are named according to their position to the thalamus. See yourself below:The diencephalon can be divided into four parts: (1) thalamus (2) subthalamus [-sub: 'inferior to”] (3) epithalamus [-epi: “superior to”](4) hypothalamus [-hypo: “under” ] The diencephalon extends posteriorly to the point where the third ventricle becomes continuous with the cerebral aqueduct and anteriorly as far as the interventricular foramina. Thus, the diencephalon is a midline structure with symmetrical right and left halves. Obviously, these subdivisions of the brain are made for convenience, and from a functional point of view, nerve fibers freely cross the boundaries.

Gross FeaturesThe inferior surface of the diencephalon is the only area exposed to the surface in the intact brain. It

is formed by hypothalamic and other structures, which include, from anterior to posterior:1. optic chiasma, with the optic tract on either side2. infundibulum, with the tuber cinereum3. mammillary bodies.

The superior surface of the diencephalon is concealed by the fornix. The actual superior wall of the diencephalon is formed by the roof of the third ventricle. The roof contains a thin epithelial membrane called ependyma. It is continuous with the rest of the ependymal lining of the third ventricle. The ependymal is involved in CSF production. It is covered superiorly by a vascular fold of pia mater, called the tela choroidea of the third ventricle. From the roof of the third ventricle, a pair of vascular processes, the choroid plexuses

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of the third ventricle, project downward from the midline into the cavity of the third ventricle. The choroid plexus is the place where the CSF is produced.

The lateral surface of the diencephalon is bounded by the internal capsule of white matter and consists of nerve fibers that connect the cerebral cortex with parts of the brainstem and spinal cord.

Since the diencephalon is divided into symmetrical halves by the slitlike third ventricle, it also has a medial surface. The medial surface of the diencephalon (i.e., the lateral wall of the third ventricle) is formed in its superior part by the medial surface of the thalamus and in its inferior part by the hypothalamus. These two areas are separated from one another by a shallow sulcus, the hypothalamic sulcus. A bundle of nerve fibers, which are afferent fibers to the habenular nucleus, forms a ridge along the superior margin of the medial surface of the diencephalon and is called the stria medullaris thalami.

1. ThalamusL. thalamus "inner chamber," from Gk. thalamos "inner chamber, bedroom"

The thalamus is a large ovoid mass of gray matter that forms the major part of the diencephalon. The thalamus is situated on each side of the third ventricle. The superior surface of the thalamus is covered medially by the tela choroidea and the fornix, and laterally, it is covered by ependyma and forms part of the floor of the lateral ventricle; the lateral part is partially hidden by the choroid plexus of the lateral ventricle. The inferior surface is continuous with the tegmentum of the midbrain.The medial surface of the thalamus forms the superior part of the lateral wall of the third ventricle and is usually connected to the opposite thalamus by a band of gray matter, the interthalamic connection (interthalamic adhesion; adhesio interthalamica; massa interrmedia). The interthalamic adhesion is found in 70-80% of humans.The lateral surface of the thalamus is separated from the lentiform nucleus by the very important band of white matter called the internal capsule.

The thalamus is a very important cell station that receives the main sensory tracts (except the olfactory pathway). It should be regarded as a station where much of the information is integrated and

relayed to the cerebral cortex and many other subcortical regions. It also plays a key role in the integration of visceral and somatic functions. The activities of the thalamus are closely related to that of the cerebral cortex and damage to the thalamus causes great loss of cerebral function.

The thalamus is actually a relay centre subserving both sensory and motor mechanisms.Thalamic nuclei (50–60 nuclei) project to one or a few well-defined cortical areas. Multiple cortical areas receive afferents from a single thalamic nucleus and send back information to different thalamic nuclei.

The anterior part of the thalamus contains the anterior thalamic nuclei, which receive the mammilothalamic tract from the mammillary nuclei. The function of the anterior thalamic nuclei is closely associated with of that of the limbic system and is concerned with emotional tone and the mechanisms of recent memory.

The medial part of the thalamus contains the large dorsomedial nucleus and several smaller nuclei. The dorsomedial nucleus has 2 connections with the whole prefrontal cortex of the frontal lobe of the cerebral hemisphere. It also has similar connections with the hypothalamic nuclei. The medial part of the thalamus is responsible for the integration of a large variety of sensory information, including somatic visceraland olfactory information and the relation of this information to one’s emotions. The lateral part is subdivided in dorsal and ventral components.

2. SubthalamusThe subthalamus lies inferior to the thalamus and, therefore, is situated between the thalamus and the tegmentum of the midbrain; craniomedially, it is related to the hypothalamus. The nucleus has important connections with the corpus striatum; as a result, it is involved in the control of muscle activity.

3. Epithalamus (dorsal thalamus)The epithalamus consists of the habenular nuclei and their connections (stria medullaris thalami & habenulointerpeduncular tract ; fasciculus retroflexus).) and the pineal gland.Habenular Nucleus

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The habenular nucleus is a small group of neurons situated just medial to the posterior surface of the thalamus. The habenular nucleus is believed to be a center for integration of olfactory, visceral, and somatic afferent pathways.Pineal Gland (Body)The pineal gland is a small, conical structure that is attached by the pineal stalk to the diencephalon. The superior part of the base of the stalk contains the habenular commissure; the inferior part of the base of the stalk contains the posterior commissure. The pineal gland possesses no nerve cells, but adrenergic sympathetic fibers derived from the superior cervical sympathetic ganglia enter the gland and run in association with the blood vessels and the pinealocytes.The pineal gland, once thought to be of little significance, is now recognized as an important endocrine gland capable of influencing the activities of the pituitary gland, the islets of Langerhans of the pancreas, the parathyroids, the adrenal cortex and the adrenal medulla, and the gonads. The pineal secretions, produced by

the pinealocytes, reach their target organs via the bloodstream or through the cerebrospinal fluid. Their actions are mainly inhibitory and either directly inhibit the production of hormones or indirectly inhibit the secretion of releasing factors by the hypothalamus. Animal experiments have shown that pineal activity exhibits a circadian rhythm that is influenced by light. The gland has been found to be most active during darkness. Melatonin and the enzymes needed for its production are present in high concentrations within the pineal gland.

4. HypothalamusThe hypothalamus is that part of the diencephalon that extends from the region of the optic chiasma to the caudal border of the mammillary bodies. It lies below the hypothalamic sulcus on the lateral wall of the third ventricle. It is thus seen that anatomically the hypothalamus is a relatively small area of the brain that is strategically well placed close to the limbic system, the thalamus, the ascending and descending tracts, and the hypophysis. Microscopically, the hypothalamus is composed of small nerve cells that are arranged in groups or nuclei. Physiologically, there is hardly any activity in the body that is not influenced by the hypothalamus. The hypothalamus controls and integrates the functions of the autonomic nervous system and the endocrine systems and plays a vital role in maintaining body homeostasis. It is involved in such activities as regulation of body temperature, body fluids, drives to eat and drink, sexual behavior, and emotion.

Relations of the HypothalamusAnterior to the hypothalamus is an area that extends forward from the optic chiasma to the lamina terminalis and the anterior commissure; it is referred to as the preoptic area. Caudally, the hypothalamus merges into the tegmentum of the midbrain. The thalamus lies superior to the hypothalamus, and the subthalamic region lies inferolaterally to the hypothalamus.The hypothalamus can be loosely divided into four distinct groups in the rostral-caudal plane of the third ventricle: preoptic (above and in front of the optic chiasm - actually telencephalic extension of the basal forebrain, but functionally considered with the diencephalon), chiasmatic (above and around the optic chiasm), tuberal (above and around the "tuber cinereum", i.e. pituitary stalk) and the posterior region which includes the mammillary bodies.When observed from below, the hypothalamus is seen to be related to the following structures, from anterior to posterior: (1) the optic chiasma, (2) the tuber cinereum and the infundibulum, and (3) the mammillary bodies.Optic ChiasmaThe optic chiasma is a flattened bundle of nerve fibers situated at the junction of the anterior wall and floor of the third ventricle. The superior surface is attached to the lamina terminalis, and inferiorly, it is related to the hypophysis cerebri, from which it is separated by the diaphragma sellae. A small recess, the optic recess of the third ventricle, lies on its superior surface.

Pituitary glandLet me do an anology here. Pituitary gland is the “switch” of the body. Look at the functions of the gland for God’s sake. Metabolism in the body, reproduction, water balance, growing…. Pituitary gland releases hormones under the influence of the hormones released by the hypothalamus.

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The hypothalamus is considered as a part of the diencephalon but they do not count the pituitary gland in the diencephalon but still we talk about it when we talk diencephalon. It lies under the hypothalamus and sits on the sella turcicae part called “fossa hypophysis”. It has a stalk called infundibulum and has two parts; the anterior pituitary and posterior pituitary. The posterior pituitary is specific as it is formed by the axons coming from the distinct nuclei in the hypothalamus. The anterior pituitary is regulated by the hypothalamus by the help of a vascular network.

Hormone Stimulated by the hypothalamic

hormone

Does

Anterior pituitary gland (Adenohypoysis)

Growth Hormone (GH) Growth Hormone-Releasing Hormone

(GHRH)

Growing

Thyroid-stimulating

hormone (TSH)

Thyrotropin-Releasing Hormone (TRH) Metabolism of the body

Adrenocorticotropic

hormone (ACTH)

Corticotropin-Releasing Hormone

(CRH)

Production and release of corticosteroids from

the adrenal glands

Prolactin (PRL) Long list of chemical substances,

inhibited by dopamine

Stimulation of milk production in breasts

Luteinizing hormone (LH) Gonadotropin-Releasing Hormone (GnRH)

Triggers ovulation

ICHS production of testosterone

Follicle-stimulating

hormone (FSH)

Gonadotropin-Releasing Hormone (GnRH)

Regulates the development, growth, pubertal

maturation, and reproductive processes of the

body

Posterior pituitary gland (Neurohypoysis)

Oxytocin Secreted from the hypothalamus and

carried to the pituitary gland

Distension of the cervix and uterus during labor,

facilitating birth, and after stimulation of the

nipples, facilitating breastfeeding.

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Antidiuretic hormone

(ADH)

Secreted from the hypothalamus and

carried to the pituitary gland

Increases water absorption in the the kidney

Tuber CinereumThe tuber cinereum is a convex mass of gray matter, as seen from the inferior surface. It is continuous inferiorly with the infundibulum. The infundibulum is hollow and becomes continuous with the posterior lobe of the pituitary gland. The median eminence is a raised part of the tuber cinereum to which is attached the infundibulum.

Mammillary BodiesThe mammillary bodies are two small hemispherical bodies situated side by side posterior to the tuber cinereum. They possess a central core of gray matter invested by a capsule of myelinated nerve fibers. They are parts of the limbic system.

5. Third Ventricle

Anterior commissure (AC)The anterior commissure (AC) of the primate brain is a tract of axons that primarily connects the right and left neocortex of the middle and inferior temporal lobes.Posterior commissure (PC)The posterior commissure bridges the upper part of the midbrain and lies adjacent to the posterior end of the third ventricle. The posterior commissure interconnects the pretectal nuclei, mediating the consensual pupillary light reflex. It is also related to superior colluculi related to light reflex.

TELENCEPHALONThe telencephalon (sometimes refered to as “cerebrum”) is the largest part of the brain. The majority

of the telencephalon is formed by the right and left hemispheres divided by the interhemispheric fissure. Each hemisphere contains the frontal, parietal, temporal, occipital lobes as well as the insula.The lateral ventricles and some part of the basal ganglia are other components of the telencephalon.

LOBES OF THE BRAINFRONTAL LOBEThe frontal lobe occupies the area anterior to the central sulcus and superior to the lateral sulcus. The superolateral surface of the frontal lobe is divided by three sulci into four gyri. The precentral sulcus runs parallel to the central sulcus, and the precentral gyrus lies between them. The superior frontal gyrus lies superior to the superior frontal sulcus, the middle frontal gyrus lies between the superior and inferior frontal sulci, and the inferior frontal gyrus lies inferior to the inferior frontal sulcus. PARIETAL LOBEThe parietal lobe occupies the area posterior to the central sulcus and superior to the lateral sulcus; it extends posteriorly as far as the parieto-occipital sulcus. The lateral surface of the parietal lobe is divided by two sulci into three gyri. The postcentral sulcus runs parallel to the central sulcus, and the postcentral gyrus lies between them. Running posteriorly from the middle of the postcentral sulcus is the intraparietal sulcus. Superior to the intraparietal sulcus is the superior parietal lobule (gyrus), and inferior to the intraparietal sulcus is the inferior parietal lobule (gyrus). The superior parietal lobule is an association area involved in

somatosensory function. The inferior parietal lobule is divided into the supramarginal gyrus gyrus [surrounding the posterior end of the posterior ramus of the Sylvian fissure], which integrates auditory, visual and somatosensory information, and the angular gyrus [surrounding the posterior end of the superior temporal sulcus], which receives visual input. TEMPORAL LOBEThe temporal lobe occupies the area inferior to the lateral sulcus. The lateral surface of the temporal lobe is divided into three gyri by two sulci. The superior and middle temporal sulci run parallel to the posterior

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ramus of the lateral sulcus and divide the temporal lobe into the superior, middle, and inferior temporal gyri; the inferior temporal gyrus is continued onto the inferior surface of the hemisphere.OCCIPITAL LOBEThe occipital lobe occupies the small area behind the parieto-occipital sulcus. The sulcus parieto-occipitalis lies between the parietal and occipital lobes in the medial surface and also lies on the lateral surface. Another sulcus is the transverse occipital sulcus lies among the unnamed gyri on the lateral surface of the lobe. The most caudal end of the occipital lobe is called occipital pole.INSULAThe insula is an area of the cortex that is buried within the lateral sulcus and forms its floor. The “little lids” surrounding the Sylvian (lateral) fissure are called “operculum. The insula has been the area of interest in studies with patients with psychiatric disorders, and is a mysterious brain structure. It has been suggested has it has functions related to autonomic system, cognition, speech, etc.

MEDIAL AND INFERIOR SURFACES OF THE HEMISPHEREThe lobes of the cerebral hemisphere are not clearly defined on the medial and inferior surfaces. However, there are many important areas that should be recognized. The corpus callosum, which is the largest commissure of the brain, forms a striking feature on this surface. The cingulate gyrus begins beneath the anterior end of the corpus callosum and continues above the corpus callosum until it reaches its posterior end. The gyrus is separated from the corpus callosum by the callosal sulcus. The cingulate gyrus is separated from the superior frontal gyrus by the cingulate sulcus.The paracentral lobule is the area of the cerebral cortex that surrounds the indentation produced by the central sulcus on the superior border. The anterior part of this lobule is a continuation of the precentral gyrus on the superior lateral surface, and the posterior part of the lobule is a continuation of the postcentral gyrus.The precuneus is an area of cortex bounded anteriorly by the upturned posterior end of the cingulate sulcus and posteriorly by the parieto-occipital sulcus.The cuneus is a triangular area of cortex bounded above by the parieto-occipital sulcus, inferiorly by the calcarine sulcus, and posteriorly by the superior medial margin. On the inferior surface of the frontal lobe, the olfactory bulb and tract overlie a sulcus called the olfactory sulcus. Medial to the olfactory sulcus is the gyrus rectus, and lateral to the sulcus are a number of orbital gyri.

BRODMANN AREASThe best accepted system of functional regionalization of the cerebral cortex was developed by the German neuroanatomist, Korbinian Brodmann (1868-1918). In 1909, Brodmann mapped the cortex into 47 unique areas, each associated with specific morphological charecteristics. Although later, investigators refined and expanded his map into more than 200 areas and assigned functional characteristics to them, Brodmann’s original classification is still widely used. The cerebral cortex is well designed with neurons, neuroglia, nerve fibers and a rich vascular supply. The organization of the six layers of the neocortex is known as cytoarchitecture, whereas each layer has a name and associated Roman numeral. It is important, however, to realize that not all areas of the cerebral cortex possess six layers. Over the past century, clinicopathologic studies in humans and electrophysiologic and ablation studies in animals have produced evidence that different areas of the cerebral cortex are functionally specialized. However, the precise division of the cortex into different areas of specialization, as described by Brodmann, oversimplifies and misleads the reader. The simple division of cortical areas into motor and sensory is erroneous, for many of the sensory areas are far more extensive than originally described, and it is known that motor responses can be obtained by stimulation of sensory areas.

Some of the Main Anatomical Connections of the Cerebral Cortex

Function Origin Cortical Area Destination

Sensory BA = Brodmann area

Somatosensory

(most to contralateral side of body; oral to

same side; pharynx, larynx, and perineum

bilateral)

Ventral posterior lateral and ventral

posterior medial nuclei of thalamus

Primary somesthetic area (BA 3, 1,

and 2), posterior central gyrus

Secondary somesthetic area; primary

motor area

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Vision Lateral geniculate body Primary visual area

(BA 17)

Secondary visual area

(BA 18 and 19)

Auditory Medial geniculate body Primary auditory area

(BA 41 and 42)

Secondary auditory area

(BA 22)

Taste Nucleus solitarius Posterior central gyrus

(BA 43)

Smell Olfactory bulb Primary olfactory area;

periamygdaloid and prepiriform

areas

Secondary olfactory area (B28)

Motor

Function Origin Cortical Area Destination

Fine movements

(most to contralateral side of body;

extraocular muscles, upper face, tongue,

mandible, larynx, bilateral)

Thalamus from cerebellum, basal

ganglia; somatosensory area;

premotor area

Primary motor area

(BA 4)

Motor nuclei of brainstem and

anterior horn cells of spinal cord;

corpus striatum

WhIte matter of the cerebral hemispheresThe white matter is composed of myelinated nerve fibers of different diameters supported by neuroglia. The nerve fibers may be classified into three groups according to their connections: (1) commissural fibers, (2) association fibers, and (3) projection fibers.Commissure FibersCommissure fibers essentially connect corresponding regions of the two hemispheres. They are as follows: the corpus callosum, the anterior commissure, the posterior commissure, the fornix, and the habenular commissure.Corpus callosumThe corpus callosum, the largest commissure of the brain, connects the two cerebral hemispheres. It lies at the bottom of the longitudinal fissure. For purposes of description, it is divided into the rostrum, the genu, the body, and the splenium.The rostrum is the thin part of the anterior end of the corpus callosum, which is prolonged posteriorly to be continuous with the upper end of the lamina terminalis. The genu is the curved anterior end of the corpus callosum that bends inferiorly in front of the septum pellucidum. The body of the corpus callosum arches posteriorly and ends as the thickened posterior portion called the splenium.The anterior commissure is a small bundle of nerve fibers that crosses the midline in the lamina terminalis. The posterior commissure is a bundle of nerve fibers that crosses the midline immediately above the opening of the cerebral aqueduct into the third ventricle; it is related to the inferior part of the stalk of the pineal gland. Association FibersAssociation fibers are nerve fibers that essentially connect various cortical regions within the same hemisphere and may be divided into short and long groups. The short association fibers lie immediately beneath the cortex and connect adjacent gyri; these fibers run transversely to the long axis of the sulci. The long association fibers are collected into named bundles. The uncinate fasciculus connects the first motor speech area and the gyri on the inferior surface of the frontal lobe with the cortex of the pole of the temporal lobe. The cingulum is a long, curved fasciculus lying within the white matter of the cingulate gyrus. It connects the frontal and parietal lobes with parahippocampal and adjacent temporal cortical regions.The superior longitudinal fasciculus is the largest bundle of nerve fibers. It connects the anterior part of the frontal lobe to the occipital and temporal lobes. The inferior longitudinal fasciculus runs anteriorly from the occipital lobe, passing lateral to the optic radiation, and is distributed to the temporal lobe. Projection Fibers

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Afferent and efferent nerve fibers passing to and from the brainstem to the entire cerebral cortex must travel between large nuclear masses of gray matter within the cerebral hemisphere. At the upper part of the brainstem, these fibers form a compact band known as the internal capsule. Once the nerve fibers have emerged superiorly from between the nuclear masses, they radiate in all directions to the cerebral cortex. These radiating projection fibers are known as the corona radiata.

INTERNAL STRUCTURE OF THE CEREBRAL HEMISPHERESLocated in the interior of the cerebral hemispheres are the lateral ventricles, masses of gray matter, the basal nuclei, and nerve fibers. The nerve fibers are embedded in neuroglia and constitute the white matter.

VENTRICLESLATERAL VENTRICLESLateral ventricles are the largest ventricles. They are paired and horse-shaped cavities separated from each other by the septum pellucidum. They are located both in the right and left hemispheres. Actually, in coherence with the shape of the hemispheres, they lie in in the shape the letter “C”.Each lateral ventricle is divided into a body, which occupies the parietal lobe, and from which anterior, posterior, and inferior horns extend into the frontal, occipital, and temporal lobes, respectively. The lateral ventricle communicates with the cavity of the third ventricle through the interventricular foramen (of Monro). 70% of the entire CSF (cerebrospinal fluid) in the brain is produced by the relatively extensive

choroid plexus of the lateral ventricles. The total volume of the entire CSF is 150 ml with a daily production of 500-750 ml. 1/5 of the CSF stays in the ventricles, and the remaining 4/5 stays in the subarachnoid space.THIRD VENTRICLEThe third ventricle is quadrilateral and slit-like. It is vertically placed between the walls of the right and left thalami. It is interrupted by a mass of grey matter massa intermedia – interthalamic adhesion; adhesio interthalamica- ; that forms a bridge between two thalami. The interthalamic adhesion is found in 70-80% of humans. FOURTH VENTRICLEThe fourth ventricle has a classical diamond shape in sagittal sections and lies between the brainstem and the cerebellum in the hindbrain. The fourth ventricle extends from the cerebral aqueduct (of Sylvius) posteriorly to the obex anteriorly. It is continuous with the central canal of the spinal cord. The lateral aspect of the fourth ventricle has three foramina; the right and left foramina of Luschka and the single,median foramen of Magendie, which drain the CSF from the fourth ventricle into the subarachnoid space. The CSF can enter the spinal cord or the subarachnoid space through these three foramina. The fluid then flows around the superior sagittal sinus to be reabsorbed via the arachnoid villi into the venous system.CisternaeIn certain areas of the brain the arachnoid mater completely diverges from the pia mater, forming expanded subarachnoid spaces which are called subarachnoid cisterns. As the CSF is circulating through the subarachnoid spaces it also enters the subarachnoid citerns, filling them. The major subarachnoid cisterns are:Cisterna magna (Cisterna cerebromedullaris) the largest subarachnoid cistern, Pontine cistern, Interpeduncular cistern, Chiasmatic cistern (cisterna basalis), Superior cistern (Cistern of the great cerebral vein).

BASAL GANGLIAThe basal ganglia comprise a distributed set of brain structures in the telencephalon, diencephalon,

and mesencephalon. The forebrain structures include the caudate nucleus, the putamen, the nucleus accumbens (or ventral striatum) and the globus pallidus. Together, these structures are named the corpus striatum.The caudate nucleus is a C-shaped structure that is closely associated with the lateral wall of the lateral ventricle. It is largest at its anterior pole (the head), and its size diminishes posteriorly as it follows the course of the lateral ventricle (the body) all the way to the temporal lobe (the tail), where it terminates at the amygdaloid nuclei.The putamen is also a large structure that is separated from the caudate nucleus by the anterior limb of the internal capsule. The putamen is connected to the caudate head by bridges of cells that cut across the internal

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capsule. Because of the striated appearance of these cell bridges, the caudate and putamen are collectively referred to as the striatum or neostriatum, and the nucleus accumbens is often called the ventral striatum.Functionally, the caudate nucleus and the putamen are considered equivalent to each other; indeed, most mammals have only a single nucleus called the striatum. The putamen and the globus pallidus are collectively called the lenticular nucleus, or lentiform nucleus. The globus pallidus is divided into two segments: the internal (or medial) segment and the external (or lateral) segment.The subthalamic nucleus is part of the diencephalon; as its name implies, it is located just below the thalamus. The substantia nigra is a midbrain structure, composed of two distinct parts: the pars compacta and the pars reticulata. The substantia nigra is located between the red nucleus and the crus cerebri (cerebral peduncle) on the ventral part of the midbrain. The pars compacta is the source of a clinically important dopaminergic pathway to the striatum; loss of neurons in this area is the cause of Parkinson’s disease. Basal Ganglia AfferentsThe striatum is the main recipient of afferents to the basal ganglia. These excitatory afferents arise from the entire cerebral cortex and from the intralaminar nuclei of the thalamus (primarily the centromedian nucleus and parafascicularis nucleus). Basal Ganglia EfferentsThe major output structures of the basal ganglia are the globus pallidus internal segment (GPint) and the substantia nigra pars reticulata (SNr). Both of these structures make GABAergic, inhibitory connections on their targets.

Functions of the Basal GangliaMOTOR FUNCTIONSThe function of the basal ganglia in motor control is not understood in detail. It appears that the basal ganglia is involved in the enabling of practiced motor acts and in gating the initiation of voluntary movements by modulating motor programs stored in the motor cortex and elsewhere in the motor hierarchy. Thus, voluntary movements are not initiated in the basal ganglia (they are initiated in the cortex); however, proper functioning of the basal ganglia appears to be necessary in order for the motor cortex to relay the appropriate motor commands to the lower levels of the hierarchy.COGNITIVE FUNCTIONSThere are a number of cortical loops through the basal ganglia that involve prefrontal association cortex and limbic cortex. Through these loops, the basal ganglia are thought to play a role in cognitive function that is similar to their role in motor control. That is, the basal ganglia are involved in selecting and enabling various cognitive, executive, or emotional programs that are stored in these other cortical areas.

BLOOD SUPPLY OF THE BRAINThe brain receives its arterial supply from two pairs of vessels, the vertebral and internal carotid

arteries, which are interconnected in the cranial cavity to produce a cerebral arterial circle (of Willis). The two vertebral arteries enter the cranial cavity through the foramen magnum and just inferior to

the pons fuse to form the basilar artery. The two internal carotid arteries enter the cranial cavity through the carotid canals on either side.

Each vertebral artery arises from the first part of each subclavian artery in the lower part of the neck, and passes superiorly through the transverse foramina of the upper six cervical vertebrae.The two internal carotid arteries arise as one of the two terminal branches of the common carotid arteries. They proceed superiorly to the base of the skull where they enter the carotid canal. Entering the cranial cavity each internal carotid artery gives off the ophthalmic artery, the posterior communicating artery, the middle cerebral artery, and the anterior cerebral artery

The cerebral arterial circle (of Willis) is formed at the base of the brain by the interconnecting vertebrobasilar and internal carotid systems of vessels. This anastomotic interconnection is accomplished by: an anterior communicating artery connecting the left and right anterior cerebral arteries to each other; two posterior communicating arteries, one on each side, connecting the internal carotid artery with the

posterior cerebral artery.

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Dr. Kaan Yücel yeditepeanatomyfhs122.wordpress.com/category/nervous-systemVenous drainage of the brain begins internally as networks of small venous channels lead to larger

cerebral veins, cerebellar veins, and veins draining the brainstem, which eventually empty into dural venous sinuses. The dural venous sinuses are endothelial-lined spaces between the outer periosteal and the inner meningeal layers of the dura mater, and eventually lead to the internal jugular veins. Also emptying into the dural venous sinuses are diploic veins, which run between the internal and external tables of compact bone in the roof of the cranial cavity, and emissary veins, which pass from outside the cranial cavity to the dural venous sinuses. The emissary veins are important clinically because they can be a conduit through which infections can enter the cranial cavity because they have no valves.

The dural venous sinuses include the superior sagittal, inferior sagittal, straight, transverse, sigmoid, and occipital sinuses, the confluence of sinuses, and the cavernous, sphenoparietal, superior petrosal, inferior petrosal, and basilar sinuses. As the transverse sinuses leave the surface of the occipital bone, they become the sigmoid sinuses, which turn inferiorly and end at the beginning of the internal jugular veins.

The paired cavernous sinuses are against the lateral aspect of the body of the sphenoid bone on either side of the sella turcica. They are of great clinical importance because of their connections and the structures that pass through them.

Structures passing through each cavernous sinus are: internal carotid artery; and abducent nerve [VI]. Structures in the lateral wall of each cavernous sinus are, from superior to inferior:

oculomotor nerve [III];trochlear nerve [IV];ophthalmic nerve [V1]; and maxillary nerve [V2].

http://imueos.wordpress.com/2010/10/08/ascending-descending-tracts-of-spinal-cordAscending tracts

SensoryDescending tracts

MotorGeneral arrangement of both tracts

1st order neuron2nd order neuron3rd order neuron

The only difference is the different locations where each order of neuron ends.Decussation is the cross-over of the tract from one side to the other. Therefore, there are instances where the left side of the body is controlled by the right brain hemisphere. Decussation occurs at different locations for each tracts.

DESCENDING TRACTSGeneral arrangement of descending tracts1st order neuronstarts at the cerebral cortex in the primary motor cortex2nd order neuron

axon of the 1st order neuron will synapse with the 2nd order neuron at the level of the brain stem, which commonly decussate (crosses over) to the opposite side.3rd order neuronThe 3rd order neuron is located in the ventral horn of the spinal cord, which will exit with the spinal nerve to supply the muscle.Types of descending tracts:

Lateral corticospinal tractAnterior corticospinal tract

Therefore, the descending tract is also known as corticospinal tract.

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Corticospinal tract arise from long axons of the pyramidal cells of the precentral gyrus (primary motor centre of the cerebral cortex) which lies in front of the central sulcusHomunculus arrangement: arranged upside down; the finer the movement, the more the cortical representationfingers, face, tongue – moretrunk, lower limbs – lessmedial surface: lower limbssuperolateral surface: everything else

1st order neuronFibres of the 1st order neuron arise from the precentral gyrusThese fibres converge and enter a small areainternal capsuleALL the fibers (from ascending & descending tracts) converge hereFunction: separates the caudate nucleus and the thalamus from the lenticular nucleus (putamen+ globus pallidus)internal capsule: bounded medially by the thalamus and caudate nucleus and bounded laterally by the lenticular nucleusParts of internal capsule (not homunculus arrangement, normal head to toe)anterior limb: head & neck fibres most anteriorposterior limb: lower limb fibres most posteriorThe descending fibres passes through the LATERAL half of the posterior limb of internal capsuleAfter the internal capsule, the fibres enter the brain stem; midbrain, pons and medulla.

2nd order neuronFibres of the 1st order neuron ends when it enters the brain stem and synapse with the 2nd order neuronThe fibres pass through the brainstem1st – through the (mid 5th) crus cerebri of midbrain2nd – through the anterior part of the pons3rd – in the medulla oblongata80-85% of the fibres cross to the opposite side: Motor decussationEnters the spinal cord

3rd order neuron2nd order neuron fibres in the medulla oblongata enters the spinal cord and synapse with the 3rd order neuronMotor decussation in the spinal tract, the crossed tract descend as the lateral corticospinal tractTherefore, the motor cortex of the cerebral hemisphere controls the opposite side of the body (L – R, R – L)contra-lateral side.In upper motor neuron lesions: above the motor decussation (above medulla), opposite side of body affectedbelow the motor decussation same side of body affected ipsilateral sideUncrossed fibres: in the spinal tract, the uncrossed tract descent as the anterior corticospinal tractits fibres cross at spinal level?

ASCENDING TRACTSTypes of ascending tracts:Spinothalamic tractsLateral spinothalamic tractpain & temperatureAnterior spinothalamic tractlight touch & pressureDorsal column tractdeep touch & pressureproprioceptionvibration sensationSpinocerrebellar tract

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posture & coordinationSPINOTHALAMIC TRACTS

1st order neuron: Arise from sensory receptors of the bodyThe fibres enter the white mater from the tip of posterior gray horn2nd order neuron:The fibres of 1st order neuron synapse with the 2nd order neuron at the substantia gelatinosa. These fibres then cross to the opposite sidePain & temperature fibres enters the lateral spinothalamic tractLight touch & pressure fibres enters the anterior spinothalamic tractThese tracts ascends to brainstem to medulla oblongata, pons and midbraintracts flattened in the brainstem: spinal lemniscusReaches the ventral posterolateral nucleus of the thalamus and ends here.3rd order neuron: The 3rd order neurons arise from the thalamus and pass through the internal capsulethalamocortical fibres pass through the medial part of the posterior limb of the internal capsuleEnters the postcentral gyrus - sensory cortex of the cerebrum, behind the central sulcus.Same homunculus arrangement; more sensitive areas in the body have a greater representation.

DORSAL COLUMN TRACT1st order neuron:

Arise from the sensory receptors of the body Fibres enter the dorsal column of the SAME side (post column of spinal cord)

ascends to the medulla oblongata (does not synapse and end here like spinothalamic tract)

Enters medulla oblongata ends in the gracile and cuneate nucleus

2nd order neuron: Starts at the gracile & cuneate nucleus of the medulla oblongataThese fibres crosses to the opposite side of the medulla oblongata.Ascends through the brain stem as flattened bundle medial lemniscusEnds in the ventral posterolateral nucleus of the thalamus.3rd order of nucleus: Arise from the thalamus Pass through the internal capsule; medial aspect of the posterior limb of internal capsule.Reaches the postcentral gyrus and ends here.

SPINOCEREBELLAR TRACT1st order neurons:Arise from the sensory receptors of the bodyEnters the spinal cordEnds in the Clarke’s Column of the posterior grey hornsynapse2nd order neurons:Arise from the Clarke’s Columnsynapse with 1st order neuronsAscends in the spinocerebellar tracts, enters the cerebellum through the interior and superior cerebellar pedunclesthe only tract that enters the cerebellumThese tracts decussate 2 times; therefore cerebellum controls same side of bodyipsilateraleg. right spinocerebellar tract controls the right side vice versa

The limbic system has two main functions: Emotional processing

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MotivationAnother function of the system; short-term memory (also emotional memory) is also important for “survival”.The limbic system works to process our emotions and is related to motivation and with its connections with the cognitive parts of the brain helps us to “use our mind” a.k.a. accomplish mental processes.The limbic system structures are telencephalic & subcortical structures. The complex network for the process of emotions and is also related to memory and learning in addition to hippocampus, amygdala and parahippocampus includes: Cingulate gyrus Hypothalamus Major areas in the prefrontal cortex Striatum Some thalamic nuclei Orbitofrontal cortex Septal area Some medial components of the midbrain (e.g. VTA) Habenula … + white matter tractsIn 1937 James Papez proposed the Papez circuit: A list of structures in the brain and a closed circuit related to emotions

Hippocampal formation (Subiculum) → fornix → mammillary bodiesMammillary bodies → mammillothalamic tract → anterior thalamic nucleusAnterior thalamic nucleus → genu of the internal capsule → cingulate gyrusCingulate gyrus → cingulum → parahippocampal gyrusParahippocampal gyrus → entorhinal cortex → perforant pathway → hippocampus.

In 1952 Paul D. McLean added Amygdala Septum Pre-frontal cortex

to the Papez circuit and came up with the idea of a system: Limbic System.In 2014, we now know that the system is more complex than it was first proposed and discussed in

mid-20th century.1939

Klüver-Bucy Syndromebilateral removal of amygdala and hippocampal formation

What happens if we remove the medial temporal lobe of an animal, a monkey? Became docile;”good monkeys”. A tendency towards oral behaviour such as attempting to ingest inedible objects.

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Hypersexualized behaviour by mounting females of the same and different species. A compulsion to attend and react to every visual stimulus No fear. Change in dietary habits

The most famous two members of the limbic system are hippocampus & amygdala.Hippocampus (sea horse; hippocampal formation) is located in the medial temporal lobe under the inferior (temporal) horn of the lateral ventricle. Amygdala (almond) resides at the tip of the temporal lobe anteriorly, and is posterior to anterior part of hippocampus.Hippocampus is the site of short-term memory. It is also an important structure in mood regulation with its connections with the hypothalamus.Amygdala is important in emotion processing with ventromedial prefrontal cortex and acts as an emotional memory box.Anterior cingulate cortex (ACC), medial part of prefrontal cortex, the basal ganglia (particularly caudate, putamen, and nucleus accumbens; the site of pleasure), anterior and dorsomedial thalamic nuclei are some of the important limbic system structures.

TWO MAIN CIRCUITS IN THE BRAIN

COGNITIVE CIRCUIT EMOTION CIRCUITDORSAL CIRCUIT VENTRAL CIRCUIT

The cognitive networks inhibit the ventral circuit.

Dorsal (cognitive) circuitHippocampusDorsolateral prefrontal cortex (DLPFC)Dorsal regions of the anterior cingulate cortex (ACC)Parietal cortexPosterior insular region

Modulates selective attention, planning and effortful regulation of affective state.Ventral (limbic) circuit structures:

AmygdalaInsula (Particularly, anterior insula)Ventral striatum Ventral regions of the anterior cingulate cortex (ACC) Orbitofrontal cortex (OFC) and medial PFC

It is possible that the altered emotional regulation or cognition found in all of these syndromes involves aberrant function of these circuits, but perhaps with different patterns on a molecular level. (Phillips et al. 2003).

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