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SPINAL CORD. Kaan Yücel M.D., Ph.D . 28. April.2014 Monday. INTRODUCTION TO NERVOUS SYSTEM. E ntire nervous system composed of neurons - PowerPoint PPT Presentation
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SPINAL CORD aan Yücel M.D., Ph.D. 28. April.2014 Monda
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SPINAL CORD

Kaan Yücel M.D., Ph.D. 28. April.2014 Monday

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INTRODUCTION TO NERVOUS SYSTEM

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Entire nervous system composed of neuronscharacterized 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.

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Dendrites are numerous short processes - carry an action potential toward the neuron’s cell body.An axon long process that carries action potential away from the cell body. Many axons ensheathed with a substance called myelin, acts as an insulator. Myelinated axons transmit impulses faster.

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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.

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Central nervous system consists of brain and spinal cord.

Peripheral nervous system consists of the sensory and motor nerves distributed throughout the body- convey information to and from the brain (via 12 pairs of cranial nerves) spinal c& ord (via 31 pairs of spinal nerves).

The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system.

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Somatic nervous system skin, joints, and skeletal muscles

Autonomic nervous system internal organs, blood vessels, and glands

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2. NEURONS & GLIAL CELLSInformation coming from peripheral receptors sense the environment

analyzed by the brain into components give rise to perceptions, some of which are stored in memory.

On the basis of this information, brain gives commands for proper action (motor, emotional, autonomic, cognitive, etc. responses). The brain does all this with nerve cells and the connections between them.

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2. NEURONS & GLIAL CELLSBehavior –achieved by concerted signaling of an enormous number of neurons. 100 billion neurons

Although nerve cells can be classified into perhaps as many as 10,000 different types, share many common features.

Nerve cells with basically similar properties produce very different actions because of precise connections with each other and with sensory receptors and muscle.

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A typical neuron has 4 morphologically defined regions:1) Cell body [also called the soma, consisting of the nucleus and perikaryon]2) Dendrites3) Axon 4) Presynaptic terminals

Each of these regions distinct function in the generation of signals. Nerve cells differ most at the molecular level. Cell body= metabolic center of the neuron

2. NEURONS & GLIAL CELLS

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Axon: main conducting unit of the neuroncapable of conveying information great distances by propagating the signal and producing the transient electrical signal, action potential. Large axons are surrounded by a fatty insulating sheath myelin, essential for high-speed conduction of action potentials.

2. NEURONS & GLIAL CELLS

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Near its end the axon divides into fine branches that have specialized swellings presynaptic terminals; 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.

2. NEURONS & GLIAL CELLS

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The point of contact is known as synapse. Neuron sending out the information presynaptic neuronNeuron receiving the information postsynaptic neuron

The space separating presynaptic from postsynaptic cell synaptic cleftMost 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.

2. NEURONS & GLIAL CELLS

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Neuron types On the basis of the number of

processes that arise from the cell body

1) Unipolar neurons: one primary process to many branches. One branch axon and other branches serve as dendritic receiving structures.

2) Bipolar neurons: 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. single axon and one or more dendritic branches typically emerge from all parts of the cell body.

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Neuron types classified functionally into three major groups

1) Afferent2) Motor 3) 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.

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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.

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Glial cellsSome of the functions of the glial cells :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.

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SPINAL CORD

Kaan Yücel M.D., Ph.D. 28. April.2014 Monday

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Vital communication link between brain and peripheral nervous system.

Sensory nerves carry messages from the body to the brain for interpretation, and motor nerves relay messages from the brain to the effectors.

Primary reflex centre, coordinating rapidly incoming and outgoing neural information.

SPINAL CORD

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SPINAL CORDBegins as a continuation of the medulla oblongata In adults, the spinal cord is 42-45 cm long (2/3 of the vertebral column)Extends from the foramen to the level of the L1 or L2 (L3 when young)Distal end of the cord (conus medullaris) icone shaped. A fine filament of connective tissue (the pial part of the filum terminale) continues inferiorly from the apex of the conus medullaris.

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SPINAL CORDAlthough 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 cauda equina continues inferiorly within the lumbar cistern containing CSF. The bundle of spinal nerve roots arising inferior to the L1 vertebra, cauda equina (L. horse tail), descends past the termination of the spinal cord.

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SPINAL CORDNot uniform in diameter along its length

Two major swellings or enlargements in regions associated with the origin of spinal nerves that innervate the upper and lower limbs.Cervical enlargement in the region associated with origins of spinal nerves

C5 to T1. Lumbosacral enlargement in the region associated with origins of spinal nerves L1 to S4.

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SPINAL CORD

The external surface of the spinal cord is marked by a number of fissures and sulci: anterior median fissure extends the length of the anterior surface;posterior median sulcus extends along the posterior surface;posterolateral sulcus on each side of the posterior surface marks where the posterior rootlets of spinal nerves enter the cord.

Internally, the cord has a small central canal surrounded by gray and white matter.

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SPINAL CORDGray matter is rich in nerve cell bodieslongitudinal columns along the cord, and in cross-section form a characteristic H-shaped appearance in the central regions of the cord.

White matter surrounds gray matter rich in nerve cell processes, form large bundles or tracts ascend and descend in the cord to other spinal cord levels or carry information to and from the brain.

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SPINAL CORDdivided 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, gray matter has pairs of horn-like projections into the surrounding white matter.

ventral horns, dorsal horns, and lateral hornsin 3-D represent columns that run the length of the spinal cord.

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SPINAL CORD

The arterial comes from two sources.

1. Longitudinally oriented vessels, arising superior to the cervical portion of the cord, descend on the surface of the cord2. Feeder arteries enter the vertebral canal through the intervertebral foramina at every level; 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.

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SPINAL CORDThe longitudinal vessels consist of: a single anterior spinal artery, originates from the vertebral arteries- passes inferiorly, approximately parallel to the anterior median fissure, along the surface of the spinal cord.Two posterior spinal arteries, 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.

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SPINAL CORDVeins 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.

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SPINAL NERVES

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SPINAL NERVES

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SPINAL NERVESAs 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.

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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.

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SPINAL MENINGESInferiorly, 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 (dural part of the filum terminale) attaches to posterior surface of vertebral bodies of coccyx.

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SPINAL MENINGESThe 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.

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SPINAL MENINGESThe 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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SPINAL MENINGESThe 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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SPINAL MENINGESThe spinal pia mater is a vascular membrane that firmly adheres to the surface of the spinal cord.


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