NERVOUS TISSUE. b) Ganglia Cerebro spinal. Spinal. Parasympathetic

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3 NERVOUS TISSUE The nervous sys. is classified into: Central nervous system (C.N.S): brain and spinal cord. Peripheral nervous system (P.N.S): a) Peripheral nerves Cranial Spinal b) Ganglia Cerebro spinal Autonomic Sympathetic Parasympathetic

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6 THE NEURON Definition: Is the structural and functional unit of the nervous tissue. Structure: The neuron or the nerve cell consists of: Cell body It contains the nucleus and surrounding cytoplasm. Processes: axon and dendrites. dendrites

7 (1) THE CELL BODY: The Cell membrane: very thin. The nucleus: Large, rounded, central and (open face type) with a prominent nucleolus.

8 The cytoplasm: Nissl granules Neurofibrils Golgi apparatus Mitochondria

9 (1) THE CELL BODY: Inclusions Melanin pigments Lipofuscin pigments: Glycogen granules Fat droplets. Centrosomes Are absent in mature nerve cells as they can not divide. Are present in young nerve cells of certain vertebrates.

10 Number: The axon Single. The dendrites Multiple. Thickness and Length: Thin & long. Thick & short. Diameter: Contour: It has a constant diameter along its length. Smooth. Their diameter decrease gradually towards their ends i.e. tapering. Irregular.

11 Branch. The axon It branches at its terminal end only i.e. terminal arborization but it may give collateral branches which arise at right angles. The dendrites They give extensive branching along their course. The branches arise at acute angles and may show spines. Conte :nt Contains mitochondria and neurofibrils Contain neurofibrils and Nissl granules.

12 Conductio n of nerve impulses : The axon carries impulses away from the cell body centrifugal conduction The dendrites carry the impulses to the cell body) Centripetal conduction

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14 Classification of the neurons (nerve cells) Classification of the neurons (nerve cells) According to the number of processes (Polarity): Unipolar nerve cells: Nerve cells are rounded with only one process. Site: mesencephalic nucleus of the trigeminal nerve. Pseudounipolar nerve cells: Nerve cells are rounded. These cells are at first bipolar, but as development proceeds the two processes of the cell meet at one side of the body forming a single process which divides in inverted T- shaped manner into 2 branches, a dendrite and an axon. The single process of each cell is convoluted at its beginning in the nerve cell forming a glomerulus in its cytoplasm. Site: spinal ganglia.

15 Bipolar nerve cells: The cells are fusiform or spindle-shaped, shaped, with 2 processes, a dendrite and an axon. Site: Retina of the eye. Spiral ganglia and vestibular ganglia in the ear. Olfactory epithelium of the nose. Multipolar nerve cells: Have many dendrites and one axon. Polygonal or stellate shaped: star-shaped shaped. Site: - Sympathetic ganglia. - Anterior horn cells of the spinal cord. Pyramidal: Site: cerebral cortex. Pyriform: flask shaped cells. Site: Purkinje cells of the cerebellum.

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17 THE NERVE FIBER Definition: It is the axon of a nerve cell. The axon may be naked or,with myelin sheath( ensheathed ) or both neurolemma. The axon (Axis Cylinder) Structure : The axon is surrounded by a membrane called axolemma and its cytoplasm is known as axoplasm. It contains neurofilaments, neurotubules and mitochondria but no Nissl granules. Length: May be very long (Golgi type I) or very short (Golgi type II). Diameter: - thick conducting impulses rapidly - Thin.. conducting impulses slowly.

18 The myelin Sheath Histological appearance: It is a white tubular covering for the axon. It is interrupted at intervals by constrictions called nodes of Ranvier. The segment between two successive nodes is called internodal segment. Chemical Structure: It is a lipoprotein sheath It appears in the form of concentric layers derived mainly from the lipid middle layer of the cell membrane of Schwann cell Staining: In H & E preparation: the fat of myelin dissolves in fat solvent (xylol) and appears as an empty space. It is stained black by osmic acid. Function: Insulation of the nerve impulses.

19 The Neurolemmal Sheath (Schwann Cells) Histological appearance: It is formed of a chain of cells forming a tube around myelin sheath. Each Schwann cell has a flat oval nucleus and corresponds to an internodal segment. The cells come in contact with the axon at the nodes of Ranvier. Function: -Insulation of nerve impulses in nonmyelinated nerve fibers. -Important role in regeneration of peripheral nerve after injury. (No regeneration of nerve fibers occurs in the CNS where the fibers are myelinated without neurolemma).

20 Types of Nerve Fibers: Naked Fibers: (non myelinated without neurolemma) e.g. - Termination of peripheral nerves. - Fibers in the gray matter. Ensheathed Fibers: -Myelinated with neurolemma: e.g. peripheral nerves. -Myelinated without neurolemma: e. g. nerve fibers in the white matter and optic nerve. -Non- myelinated with neurolemma: e.g. sympathetic nerve fibers.

21 Structure of a peripheral Nerve Trunk: Nervous component: Groups of nerve fibers (myelinated axons with neurolemma) arranged in bundles. -In Hx. & E. stained section: Each fiber shows a centrally stained acidophilic axon, surrounded by an empty space of the dissolved myelin and a thin outer pink rim of The nuclei of these.cell cytoplasm Schwann.cells may be seen if they are cut in the section -In osmic acid stained section: The myelin sheath of the nerve fibers appears.as rounded black circles C. T. component: -Epineurium : It is a dense C. T., which surrounds the whole nerve trunk. -Perineurium: It is a dense C. T., which surrounds the bundles of nerve fibers. -Endoneurium: (Henle s sheath) It is a delicate loose C. T. between the individual nerve

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27 GANGLIA Definition: A nerve ganglion is a collection of nerve cells and nerve fibers, covered by a C. T. capsule, outside the C. N. S. NB: a collection of nerve cells inside the C. N. S is called nucleus.

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29 Spinal ganglion Sympathetic ganglion Site : C.T. Capsul.

30 Nerve cells: Type: Size: Arrangement: Number: Nuclei: Satellite Cs Glomerulus : Spinal ganglion Sympathetic ganglion

31 Nerve Fiber s Spinal ganglion Thickly myelinated. Widely separated from each other Parallel to the capsule. absent Synapse: (as the fibers are the peripheral processes of the nerve cells whose axons enter the C.N.S) Sympathetic ganglion Thinly or non myelinated Close to each other..irregularly distributed Present Synapse fibers preganglionic) synapse with the ganglion cells whose axons form. )the postganglionic fibers

32 Spinal Sympathetic ganglion Blood supply: ganglion Function: Acts as relay for different sensations before their entrance into the spinal cord. Acts as relay for different motor functions arising from the spinal cord.

33 Nervous tissue Practical Slides

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