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GANGLIA A collection of nerve cell bodies outside the central nervous system is called a ganglion. The ganglia form subsidiary(assist,help) nerve centers which receive and send out nerve fibers. Usually occur in the form of oval structures associated with peripheral nerves. Microscopically and functionally ganglia are divided into two types: 1. Craniospinal (sensory) ganglia 2. Autonomic ganglia A connective tissue capsule surround both ganglion The body of each ganglion cell is enveloped be a layer of small flattened cells called satellite cells CRANIOSPINAL GANGLIA This group include cranial and spinal ganglia. The spinal ganglia are located in the dorsal roots of spinal nerves, while the cranial ganglia are situated in the path of some cranial nerves. The ganglion cells are neurons of pseudo-unipolar type. Each ganglion give rise to a single process which makes several irregular turns around the cell body and then bifurcates in t-shape. One of the branches functions as a dendrite and passes in a spinal or cranial nerve to periphery where it terminates at the receptor organ. The other branch which is thinner of the two becomes a functional axon and passes to the central nervous system. CRANIOSPINAL GANGLIA The ganglia has two zones 1. Cortical zone 2. Medullary zone The nerve cell bodies are arranged in peripheral (cortical) zone of ganglion. The central(medullary) zone has a great number of nerve fibers but is devoid of nerve cell bodies. Ganglia AUTONOMIC GANGLIA This group has the ganglia associated with the sympathetic and parasympathetic divisions of the autonomic nervous system. These ganglia contain multipolar neurons having many branched dendrites and a single myelinated axon. Dendrites of these neurons receive synapses from the incoming preganglionic nerve fibers, while their axons pass out as postganglionic fibers. The cell bodies here are evenly distributed and do not show peripheral localization seen in craniospinal ganglia. Gray and white matter Brain and spinal cord are composed of gray and white matter Gray matter. The gray matter mainly consist of nerve cell bodies. But it also has myelinated,unmyelinated nerve fibers, astrocytes, oligondendrocytes and microglial cells. white matter: It does not have cell bodies consists only of myelinated and unmyelinated nerve fibers. It also contain oligodendrocytes, astrocytes and microglial cells. The white color is due to predominance of myelinated nerve fibers SPINAL CORD Roughly oval in shape, more flattened ventrally than dorsally. In the center there is a circular cavity called central canal. Ventrally there is a deep cleft or fissure called ventral median fissure. Gray matter: Gray matter of spinal cord is so arranged that it gives the appearance of an H. The two dorsal limbs of the H are called posterior horns. The two ventral limbs of H are called anterior horns. The posterior horn contains sensory neurons while the anterior horn motor neurons concerned with innervation of skeletal muscles. SPINAL CORD The central canal is situated in bar of H. The gray matter present dorsal to the central canal connects the two posterior horns and is known as dorsal gray commissure Similarly ventral to central canal is the ventral gray commissure. In all thoracic and upper one or two lumber segments, the gray matter of the spinal cord shows an additional horn called lateral horn which is situated between the ant/posterior horns. The lateral horn contains motor neurons which give rise to preganglionic sympathetic fibers. SPINAL CORD white matter: Outer to the gray matter of the spinal cord is the white matter of the spinal cord. On each side the white matter can be divided into the following parts: 1. Dorsal white column: also called dorsal faniculus which lies between the dorsal medial septum and gray horn. 1. Ventrolateral white column: Lies between the posterior horn and the ventral median fissure. This column is further divide by anterior gray horn into I. Ventral white column II. Lateral white column CEREBELLUM Cerebellum consist of two hemispheres with a central vermis. The surface of the cerebellum shows many transverse fissures. These fissure divide the substance of the cerebellum into lobules. The gray matter of cerebellum is located on the surface as a thin cortex overlying the centrally placed white matter. But there are also masses of gray matter called nuclei, located within the white matter in the deep central parts of the hemispheres. CEREBELLUM Cerebellar cortex: Section of cerebellar cortex show three layers which are given below A-Molecular layer: Mainly contain cell processes. It also contain dendritic arborizations(tree like branching) of various cells, unmyelinated axons. Cell population of molecular layer is very low. Tow varieties of neurons may be observed in this layer 1. Stellate cells Stellate cells have small star shaped perikarya(cell body). Each cell has many short dendrites and a fine unmyelinated axon. The axon extends transversely to make synapses with the dendrites of the purkinje cells CEREBELLUM……. A-Molecular layer……… 2. Basket cells They also have small perikarya which give rise to numerous branching dendrites that ascend toward the surface. The unmyelinated axon of a basket cell gives off many descending branches which form basket like terminal arborizations around the bodies of the purkinje cells. CEREBELLUM B-Purkinje cell layer: This layer lodges the cell bodies of large multipolar neurons called purkinje cells. Each purkinje cell contains a vesicular nucleus with a prominent nucleolus. The dendritic tree arises from the apex of the perikaryon as two or three large primary dendrites which enter the molecular layer and branch repeatedly to form a fanshaped arborization. The axon arises from the base of the cell acquires a myelin sheath and passes through granular layer to enter underlying white matter. Most of the axons of the purkinje cell terminate in the deep cerebellar nuclei. CEREBELLUM 3-Granular layer: This layer contains a dense population of small neurons called granule cells. The cytoplasm of granule cells cannot be seen under H&E sections and the granular layer appear to be composed of closely packed nuclei. Granular layer also shows irregularly scattered lighter staining areas called glomeruli or islands. Each granule cell gives rise to four or five short dendrites. The unmyelinated axon of granular cell ascend to the molecular layer where it bifurcate into two branches . These fibers make synapses with the dendrites of the purkinje cells. This layer also has Golgi type II cells. CEREBELLUM Afferent fibers of the cerebellum: Climbing fibers: These fibers originate in the inferior olivary nucleus of the medulla oblongata. Upon their entry into the cerebellum these fibers run in the white matter to reach the cerebellar cortex where they synapse with the dendrites of purkinje cells in the molecular layer. Mossy fibers: These fibers originate in the spinal cord or in the brain stem. They terminate in the glomeruli of the cerebellar cortex where they make synaptic contact with dendrites of the granule cells and axons of the Golgi type II cells. Layers of cerebellar cortex CEREBRUM Like cerebellum the cerebrum also has a cortex of gray matter and a central area of white matter in which are found collections of gray matter called nuclei. Cerebral cortex: The structure of cerebral cortex varies in different parts of cerebrum. The olfactory cortex and cortex of hippocampus are simples in structure consisting only of two layers. Deeper layer Containing Rest of the cortex is covered by neocortex which consist of six superimposed layers. nerve cell bodies covered by a layer composed of dendrites of nerve cells, this cortex is known as allocortex. CEREBRUM CELLS OF CEREBRAL CORTEX: Cells of the cerebral cortex are divided into following two types: 1. Pyramidal cells 2. Non-pyramidal cells 1.Pyramidal cells: Its indicated from their name that these multipolar neurons have pyramid shape cell bodies. Each pyramidal cell has a large vesicular nucleus. The cytoplasm has abundant Nissl granules. These cells have one main dendrite which passes outward to end in the most superficial layer of the cortex . The axon emerges from the center of the base and runs into the underlying white matter . CEREBRUM 2-Non-pyramidal cells: This group include the following cells 1. stellate (granule) cells 2. Horizontal cells 3. Martinoti cells: 1-stellate (granule) cells: These cells have small polygonal perikarya Because of their small size they are also called granule cells Each cell give rise to a number of small dendrites passing in various directions and a short axon which ramify close to the cell body. CEREBRUM 2-Non-pyramidal cells……… 2-Horizontal cells: Small, horizontal placed fusiform cells found in the most superficial cortical layer. It has many short dendrites and a long axon which make contact with dendrites of pyramidal cells. 3-Martinoti cells: Small, multipolar cells found in deeper layers of cerebral cortex. A Martinoti cells has short dendrites it has long axon which ascend toward the cortical surface to end in more superficial layer, commonly reaching the outer most layer of the cortex. LAYERS OF CEREBRAL CORTEX The neocortex has six horizontally placed layers which are given as 1-Molecular or flexiform layer: This layer is composed of cell processes of the cells lying in deeper layer. 2-External granular layer: This layer contains large number of small pyramidal cells and numerous closely packed stellate(granule) cells. 3-Pyramidal cell layer: This layer also called external pyramidal layer and is composed of mainly pyramidal cells, some granule cells are also present. 4-Internal granular layer: This layer consist of closely packed stellate cells. There is a high concentration of horizontally arranged nerve fibers known as outer band of baillarger. LAYERS OF CEREBRAL CORTEX……….. 5-Ganglionic layer: Also called internal pyramidal layer contains large number of pyramidal cells. Scattered among the pyramidal cells are stellate and martinoti cells. This layer also contain a large number of horizontally running nerve fibers which form the inner band of Baillarger. 6-Multiform layer: As the name indicates this layer is composed of neurons of many shapes. It contains pyramidal cells, stellate cells and martinoti cells. MENINGES 1. 2. 3. The brain and spinal cord are covered by three membranes called meninges. Which are given below Pia matter (innermost) Arachnoid matter(external to the pia) Dura matter (outermost) MENINGES 1-Pia mater: (Latin Pia =delicate mater=mother) The pia mater is a thin layer of connective tissue containing bundles of collagenous fibers and some fine elastic fibers. Towards the subarachnoid space the pia mater is lined by a continuous layer of flat(squamous) cells that resemble the mesothelial lining of the body cavities. MENINGES 2-Arachnoid mater The arachnoid mater consists of a thin layer of connective tissue, composed chiefly of delicate collagenous fibers: a few elastic fibers are also present. The arachnoid is connected to the pia mater by a cobweb-like network of delicate connective tissue trabeculae The inner and outer surfaces of the arachnoid mater and the trabeculae are covered by a continuous lining of flat cells similar to those covering of pia mater. MENINGES 3-Dura mater: This layer is of tough consistency and is composed of dense connective tissue. This connective tissue mainly consists of collagenous fibers mixed with some elastic fibers. The inner surface of dura mater is covered by a lining of flat cells of mesenchymal origin. The dura mater also lodges a number of sensory nerves and blood vessels .