Functions: The spinal cord per-forms two general functions. Briefly, it provides conduction routes to and from the brain and serves as the integrator, or reflex center, for all spinal reflexes (2)

Dura mater: made of strong white fi-brous tissue, serves as the outer layer of the meninges and also as the inner peri-osteum of the cranial bones.

Arachnoid membrane, a delicate, coweb like-layer, lies between the dura matter and the pia matter or innermost layer of the meninges

Pia matter: innermost layor of the menin-ges. The transparent pia matter adheres to the outer surface of the brain and spi-nal cord and contains blood vessels

Cerebrospinal fluid: In addition to its bony and membranous coverings, nature has further protected the brain and spinal cord against injury by providing a cushion of fluid both around the organs and within them, it also a reservoir of circulating fluid that, along with blood, the brain monitors for changes in internal environ-

ment.

Where is it found : cerebrospinal fluid is found in the subarachnoid space around the brain and spi-nal cord within the cavities and canals of the brain and spinal cord. Which are called ventricles

Spinal cord: the spinal cord lies in the spinal cavity, extending from the foramen magnum to the lower border of the first lumbar vertebra, a distance of about 45 cm in the average body. The spinal cord does not completely fill the spinal cavity.

Volume 1, Issue 2 10.29.12

ANATOMY & PHYSIOLOGY

WEEKLY

Inside this Issue

CNS 1,2,3 Page 1

PNS 5,6,7,8 Page 2

CNS 4,5,6 Page 3

CNS 7,8,9 Page 4

PNS 1,2,3,4 Page 5

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Inside the peripheral nervous system there are two subdivisions, the so-matic nervous system and the autonomic nerv-ous system. The auto-nomic nervous system includes fibers that con-nect the CNS to viscera, such as the heart, stom-ach and glands. Within the automatic nervous system it is divided into another two parts the sympathetic nervous sys-tem and the parasym-pathic nervous system.

The autonomic nervous system functions inde-pendently and without conscious effort. Afferent nerves are the sensory nerves that travel away from the central nervous system and efferent nerves are the motor nerves that travel toward the central nervous sys-tem. As a whole the Auto-nomic Nervous System sends impulses from the central nervous system to smooth muscle, cardiac muscle, and glands. The

purpose of the sympathetic nervous system is to prepare the body for physical activity. The purpose of the parasympathic nervous system is to active vegetative functions such as digestion, defecation, and urination. (1)

“The

autonomic

function

functions

independe

ntly”

Page 2 ANATOMY & PHYSIOLOGY WEEKLY

Autonomic Nervous System

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Efferent nerves travel toward the CNS

Afferent nerves travel away from the CNS

the cerebrum. Inferior cerebellar peduncles composed cheifly if reacts into the cerebellum from the medulla and cord. Middle CP are composed almost entirely of tracts into the cerebellum from the pons, that is, ponto-cerebellar tracts. Superior CP is composed to princi-pally of tracts from den-tate nuclei in the cerebel-lum through the red nu-cleous of the midbrain to the thalamus. The func-tions of the cerebellum is that they perform three general functions that has to deal with the control of skeletal muscles. They act with the cerebral cor-tex to produce skilled movements by coordinat-ing the activities of groups os muscles. They help control posture. It func-tions below the level of consciousness to make movements smooth. They also control the skeletal muscles to maintain bal-

ance.

The Thalamus and the Hypothalmus are also im-portant to the brainstem. The thalamus is a dumb-bell shaped mass of grey matter that makes up many nuclei. They play two parts in the mecha-nism responsible for sensation. It impulses from appropriate receptors, on reaching the thal-mus, produce conscious recog-nition of the crude,less crtical sensation of pain, temperaure and touch. The neurons whose dendrites and cell bodies lie in certain nuclei of the thalamus relay all kinds of sensory im-puses. Plays a part in the mechanism responsible for emotion, in the arousal or alert-ing machanism and a part in the mechanism that produce complex reflex movements. It is involved in regulation of the homeostatic control. Neuroen-docrine role in conjunction with the pituitary gland as well as by its influence on the the autonomic nervous system, which helps regu-late body temperature, the cardiovascular system, and food and water intake.

The Brainstem functions as our own privet is located at the lower part of the brain directly connected to the spinal cord. The brainstem is like the spinal cord, performs sensory, motor, and reflex functions. It is the pathway for all fiber tracts passing up and down from peripheral nerves and spinal cord to the upper areas of the brain. The Medulla Oblongata is a relay station for the crossing of motor tracts between the spinal cord and the brain. It also contains the respiratory, motor and cardiac functions, as well as several mech-anisms of reflex activities such as coughing, swallowing and vomiting. The midbrain is the nerve pathway of the cerebral hemisphere and contains auditory and visual reflex centers. The pons is the area that links different parts of the brain and seves a relay station from the me-dulla to the higher cortical struc-tures of the brain.

The Cerebellum is the second larg-est part of the brain. A transverse fissure separates the cerebellum from the cerebrum. The Gyri of the cerebellum are much more slender and less prominent than those of

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Somatic Motor Pathways con-sists of motor neurons that con-duct impulses from the central nervous system to somatic effec-tors.

The set of coordinated com-mands that control the pro-grammed muscle activity mediat-ed by extrapyramidal pathways is often called a motor program.

Somatic Sensory Pathways

Primary sensory neurons of the relay conduct from the periphery to the central nervous system.

Secondary sensory neurons conduct from the cord/brainstem up to the thala-mus.

Tertiary sensory neurons conduct from the thalamus to the post central gyros of the parietal lobe, the somatosensory area.

Each side of the brain registers sensa-tions from the opposite side of the brain.

Crude touch and pressure sensations are functions of the spin thalamic path-way.

Cerebral Cortex

The cerebrum is the largest and uppermost division of the brain, con-sist of two halves, the right and left cerebral hemispheres.

Composed of gray matter

Functions of Cerebral Cortex

Consciousness, language, emotion and memory are also all controlled by the cerebral cortex

Mechanisms that control voluntary movements are extremely complex

and imperfectly under-stood (1)

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Cranial Nerves- Connect to the undersurface of the brain, mostly on the brainstem. There are 12 different cranial nerves: (2) Olfactory (sensory) Optic (sensory) Oculomotor (Motor) Trochlear (Motor) Trigeminal (Mixed) Abducens (Motor) Facial (Mixed) Vestibulocochlear (Sensory) Glossopharyngeal (Mixed) Vagus (mixed)

Hypoglossal (Motor)

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At each skin surface area supplied by sensory fibers of a given spinal nerve is called a dermatome, a name that means “skin section”. (2)

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A Myotome is a skeletal muscle or group of muscles that receives mo-tor axons from a given spinal nerve. (2)

The Ventral rami of most spinal nerves—all but nerves T2 through T12--- subdivide to form complex networks called Plexuses. (2)

Each of the 31 pairs of spinal nerves exits the spinal cavity from the inter-vertebral foramina. The names of the vertebrae are given on the left and the names of the corresponding spinal nerves on the right. (2)

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