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Lec3 Histology Nervous System Dr.Elham Majeed Al Hadithy Histology of Nerve the Nervous System human body, is formed by a network of more than 100 million nerve cells (neurons), assisted by many more glialcells. neurons, forming a very complex system for communication. are highly specific combinations of elements that make up systems of various sizes and complexities. communications network. system,consisting of the brain and the spinal cord, and the peripheral nervous system,composed of nerve fibers and small aggregates of nerve cells called nerve ganglia Structurally,nerve tissue consists of two cell types:nerve cells,or neurons, Usually show numerous long processes, and several types of glial cells which have short processes,support and protect neurons, and participate in neural activity,neural lnutrition, and the defense processe softh ecentral nervous system. amodification of electrical potential that may be restricted to the place that received the stimulus ray be spread(propagated)throughout the neuron by the plasma membrane.This propagation,called the action potential,or nerveimpulse,iscapable of traveling long distances;it transmitsin form at ion too the neurons,muscles,and glands. 1 Lec3 Histology Nervous System Dr.Elham Majeed Al Hadithy Central Nervous System (CNS) skull,and the spinal cord,which is contained within the vertebral canal. tissue of the CNS does not contain connective tissue other than that in the three meninges(duramater,arachnoid membrane and piamater)and in the walls of large blood vessels. observed,which is quite unlike other tissues.Because of the absence of connective tissue,fresh CNS tissue has avery soft,some what jelly-like consistency. cells,neurones,and supporting cells,glia. The Central Nervous System spinal cord.It has almost no connective tissue and is therefore a relatively soft, gel-like organ. regions that are white (white matter) and that are gray (gray matter). responsible for these differences: The main component of white matter is myelinatedaxons and the myelin-producing oligodendrocytes. 2 Lec3 Histology Nervous System Dr.Elham Majeed Al Hadithy Meninges The delicate,innermost,mesh-like layer of the meninges.The pia mater closely envelops the entire surface of the brain,running down into the fissures of the cortex. s with the ependyma which lines the ventricles to form choroid plexuses that produce cerebrospinal fluid.In the spinal cord,the pia mater attaches to the dura mater by the denticular ligament sthrough the arachnoid membrane Gray and White Matter Microscopically, the CNS contains 2 neural elements: d unmyelinated axons. Gray matter contains neuronal cell bodies,dendrites,and the initial unmyelinated portions of axons and glial cells. cerebellum,forming the cerebral and cerebellar cortex neuronal cell bodies forming islands of gray matter embedded in the white matter are called nuclei 3 Lec3 Histology Nervous System Dr.Elham Majeed Al Hadithy matter has six layer s of cells with different forms and sizes.Neurons of some regions of the cerebral cortex register afferent(sensory)impulses;in other regions,efferent(motor)neurons generate motor impulses that control voluntary movements. cerebral cortex are related to the integration of sensory information and the initiation of voluntary motor responses Cerebral Cortex Allows for sensation, voluntary communication, recognition, and more. movement, self-awareness, ain mass, but only 2-3 mm thick. functions of the opposite side (contralateral side) of the body Cerebellum •Lies inferior to the cerebrum and occupies the posterior cranial fossa. •2nd largest region of the brain. •10% of the brain by volume, but it contains 50% of its neurons •Has 2 primary functions: 1.Adjusting the postural muscles of the body •Coordinates rapid, automatic adjustments, that maintain balance and equilibrium 4 Lec3 Histology Nervous System 2.Programming and fine-tuning subconscious and conscious levels movements Dr.Elham Majeed Al Hadithy controlled at the •Refines learned movement patterns by regulating activity of both the pyramidal and extrapyarmidal motor pathways of the cerebral cortex •Compares motor commands with sensory info from muscles and joints and performs any adjustments to make the movement smooth Cerebellum extensive dendrites can receive up to 200,000 synapses. a branching array that in a sectional view resembles a tree –for this reason, it’s called the arbor vitae In cross sections of the spinal cord,white matter is peripheral and gray matter is central, assuming the shape of an H. His an opening, the central canal,which is a remnant of the lumen of the embryonic neural tube. forms the anterior horns.These contain motor neurons whose axons make up the ventral roots of the spinal nerves. receive sensory fibers from neurons in the spinal ganglia (dorsal roots). Spinal cord Spinal cord neurons are large and multipolar, especially in the anterior horns, where large motor neurons are found The gray matter contains neuronal bodies and abundant cell processes,where as the white matter 5 Lec3 Histology Nervous System Dr.Elham Majeed Al Hadithy consists mainly of nerve fibers whose myelin sheath was dissolved by the histological procedure Ganglion cells will typically be several times larger than other cells in the ganglia nucleus.Only the cells immediately surrounding the ganglion cells as one flattened layer are satellite cells. of course in contact with other parts of the nervous system and with the peripheral tissues which they innervate. Consequently,nerve fibers will be visible close too within the ganglion. Peripheral Nerve identify the axon running in its myelin sheath, nodes of Ranvier and Schwann cell nuclei. nerve, should be visible and identifiable in both longitudinal and transverse sections. ely cut preparations give a good picture of the axon in the middle of a ring-like structure (sometimes fussy), which represents the remains of the myelin sheath. 6