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THE NERVOUS SYSTEM I: CNS FUNCTIONS • collection of sensory input • integration • motor output ORGANIZATION STRUCTURAL • Central nervous system (CNS) • Peripheral nervous system (PNS) FUNCTIONAL • sensory division • motor division – autonomic – somatic REGIONS OF THE BRAIN CEREBRAL HEMISPHERES • they are the largest part of the brain • they are paired • they have ridges of tissue, called gyri • the gyri are separated by grooves called sulci • large regions of the brain are called lobes • Lobes are separated by deeper sulci TISSUE OF THE CEREBRAL HEMISPHERES • the outermost layer is called gray matter or cortex • deeper is located the white matter, composed of fiber tracts (bundles of nerve fibers), carrying impulses to and from the cortex • corpus callosum is a very large fiber tract connecting the cerebral hemispheres • the basal nuclei are made from gray matter and are located deep within the white matter • they help the motor cortex in the regulation of voluntary motor activies CEREBELLUM The cerebellum has 2 hemispheres and a convoluted surface. It has an outer cortex made from gray matter and an inner region of white matter. It provides precise coordination for body movements and helps maintain equilibrium. Spinal cord • • • • • • • • Long 42 cm It is a two-way conduction pathway to the brain It is a major reflex center Extends from foramen magnum to L2 vertebra Gives rise to 31 pairs of spinal nerves Has 2 enlargements: cervical and lumbar Does not reach to end of the vertebral canal Has cauda equina (collection of spinal nerves at the end of the spinal cord) Gray matter of the spinal cord : • 2 posterior dorsal horns dorsal root • 2 anterior (ventral) horns ventral roots • Central canal • Dorsal root ganglion: contains bodies of sensory neurons • Ventral horns: contain bodies of motor neurons • Dorsal and ventral roots fuse to form the spinal nerves. White matter of the spinal cord : • 3 columns: posterior, lateral, anterior. • They contain tracts (axons) • Sensory (afferent) tracts • Motor (efferent) tracts PROTECTION OF THE CNS • • • THE CNS IS PROTECTED BY: the skull and the vertebral column (bone) meninges (membranes) cerebrospinal fluid (watery cushion) • • • THERE ARE 3 LAYERS OF MENINGES: dura mater (outside membrane) arachnoid mater (middle membrane) pia mater (inner membrane) MENINGES DURA MATER • • • • • doule-layered membrane the outermost layer is attached to the inside surface of the skull bones (periosteal layer) the internal layer (meningeal layer) covers the surface of the brain and the spinal cord the two layers are fused together, except in 3 places where they form channels (dural sinuses) where venous blood fromthe brain is collected in some places the inner dural membrane forms folds (falx cerebri) that attaches the brain to the cranial cavity ARACHNOID MATER • • • • • • looks like cobweb has threadlike extensions (arachnoid villi) that attach it to the innermost membrane (pia mater) the arachnoid villi absorb cerebrospinal fluid contains the subarachnoid space filled with cerebrospinal fluid PIA MATER thin, delicate membrane attached to the surface of the brain CEREBROSPINAL FLUID CSF is constantly produced by the choroid plexuses inside each ventricle. Inside the brain, CSF flows from the lateral ventricles in the 3rd and 4th ventricle. From the 4th ventricle, part of the the CSF flows down in the central canal of the spinal cord. Most of the CSF drains from the 4th ventricle in the subarachoid space around the brain and returns to the dural sinuses through the arachnoid villi. NERVOUS SYSTEM II: PNS CRANIAL NERVES 12 pairs • 4 pairs are mixed • • trigeminal n. (5th) • facial n. (7th) • glossopharyngeal n. (9th) • vagus n. (10th) • 5 pairs are motor: • occulomotor n. (3rd) • trochlear n. (4th) • abducent n. (6th) • accessory n. (11th) • hypoglossal n. (12th) • 3 pairs are sensory: • olfactory n. (1st) • optic n. (2nd) • vestibulocochlear n. (8th) Spinal Nerves and Nerve Plexuses • 31 pairs of spinal nerves • named for the region of the spinal cord from which they arise • each spinal nerve is attached by two roots: dorsal (sensory) & ventral (motor) • each spinal nerve divides into a dorasl and ventral ramus • The rami contain both sensory and motor fibers • the dorsal rami are distributed individually innervate the skin and muscles of the posterior body trunk • the ventral rami form plexuses (except in thoracic region where they form the intercostal nerves), and supplythe anterior part of the body •