Functional Organization of Nervous Tissue

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Internode: • Saltatory conduction: action potential jump from on node to the other. • Composition of myelin sheath: protein lipids and. H2O. Lipids are cholesterol,.

Nervous Tissue Presented by: Dr. Jeevan Kumar Giri 2nd year PG Scholar Department of Rachana Sharir SDM College of Ayurveda & Hospital, Hassan.

Tissue • • • •

Epithelial tissue Connective tissue Muscular tissue Nervous tissue

By Dr. Jeevan Kumar Giri

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The Nervous System • Introduction – It is the chief controlling and coordinating system of the body that response voluntarily or involuntarily against the stimulus. – Sensory perceptions, mental activities, stimulating muscle movements, secretions of many glands etc

• Components – Brain, spinal cord, nerves, sensory receptors

• Subdivisions – Central nervous system (CNS) – Peripheral nervous system (PNS) – Autonomic Nervous system (ANS).

By Dr. Jeevan Kumar Giri

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Central Nervous System • Consists of – Brain • Located in cranial cavity of skull

– Spinal cord • Located in vertebral canal

• Brain and spinal cord – Continuous with each other at foramen magnum

By Dr. Jeevan Kumar Giri

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Peripheral Nervous System • In include 12 pairs of cranial nerves – I, II, VIII – V, VII, IX, X – III, IV, VI, XI, XII

• And 31 pairs of spinal nerves. – C8, T12, L5, S5, Co1 – All are mixed By Dr. Jeevan Kumar Giri

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Autonomic nervous system • Sympathetic nervous system • Parasympathetic nervous system

By Dr. Jeevan Kumar Giri

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General Organization of the nervous system

By Dr. Jeevan Kumar Giri

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Cells of Nervous System • NEURONS • NEUROGLIA

• Neurons or nerve cells – Structural & functional unit of NS. – Specialized for reception, integration, interpretation and transmission of the information.

• Neuroglia or glial cells By Dr. Jeevan Kumar Giri

– Support and protect neurons

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Neurons Cell body/Perikaryon/Soma • Cell membrane –outer covering of soma • Cytoplasm –consist of large central nucleus, numerous mitochondria, lysosomes, centrioles and Golgi complex. • Nissl substances/bodies –granular material stained by basic dyes. Composed of RER • Neurofibrils –cytoskeleton of the cells. Consist of microfilament and microtubules. • Pigmented granules–neuromelanin, lypocrome and lipofuscin • Nucleus –contain genetic material By Dr. Jeevan Kumar Giri

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• Cell process/neurites • Axon –one longer process from cell. – – – –

Cell membrane is axolemma Cytoplasm is axoplasm Long single cell process Terminate either in effector organ or ganglion, or in synpse. – Carry impulse away from cell.

• Dendrites –Numerous Short cell process. – Terminate in the cell body – They carry impulse toward the cell By Dr. Jeevan Kumar Giri

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• Axon Hillock: part of cell body. Free form Nissl granules. • Initial segment: initial part of the axon. – This is the site of action potential generation – Receive axo-axonal synapse.

By Dr. Jeevan Kumar Giri

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By Dr. Jeevan Kumar Giri

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Structural architecture of NS Cell body/Soma • Gray matter in CNS – Cortex – Nucleus – Horns of spinal cord

• Gray matter of PNS – Ganglion

By Dr. Jeevan Kumar Giri

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Cell process/Neurites • White matter in CNS – Fibers (commissural, association, projection) – peduncle – Tracts (Ascending, descending) – White column of spinal cord

• White matter in PNS – Nerve fibers

By Dr. Jeevan Kumar Giri

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Types of Neurons Anatomical /Morphological classification I. On the basis of number of cell process  Unipolar neurons –mesencephalic nucleus of Vth CN.

 Bipolar neurons -neurons of olfactory mucosa, retina, sensory ganglia of IX th cranial nerve.

By Dr. Jeevan Kumar Giri

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 Pseudo unipolar neurons –dorsal

sensory ganglion of Spinal cord.  Multipolar neurons – all

other motor neuron that controls the skeletal muscles. By Dr. Jeevan Kumar Giri

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By Dr. Jeevan Kumar Giri

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II. On the basis of length of axon 1. Golgi type I:  Principal or projecting neurons are also known as type I or Golgi type I neurons.  neurons having long axon (>1 M), that connects to different parts of NS.  forms the tracts and fibers of CNS.  Giant pyramidal cell of the motor cortex in cerebrum.  Nerve fibers of PNS  Purkinje, Golgi cell of cerebellum  Motor neuron of ventral horn cell of spinal cord. By Dr. Jeevan Kumar Giri

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2. Golgi type II: – Intrinsic neurons are also known as type II or Golgi type II neurons.

– Intrinsic neurons have very short axons. – These neurons are interneurons and are considered to have inhibitory function. – They are abundant in the cerebral and cerebellar cortex. By Dr. Jeevan Kumar Giri

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III. Amacrine neuron: They don’t have true axon but posses numerous neurites. Unusual neuron Eg: amacrine neuron of retina.

By Dr. Jeevan Kumar Giri

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III. On the basis of the Myelinated

Myelinated : • Forms the insulation • By Schwann cell or oligodendrocyes • Mesaxone • Lipid diposit in between the layers adjacent layer of the membrane of the Schwan cell. Together forms the myelin sheath. • Outside the myelin sheath the layer of the cytoplasm of the Schwan cell persist called the neurilemma. By Dr. Jeevan Kumar Giri

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• Node of Ranvier: Gap between two successive myelinated short segment of the axon. • Internode: • Saltatory conduction: action potential jump from on node to the other • Composition of myelin sheath: protein lipids and H2O. Lipids are cholesterol, phospholipids and glycosphingolipids etc.

By Dr. Jeevan Kumar Giri

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• The composition & structure of the myelin sheath formed by the oligodendrocyes and Schwann cell are difference. • The neurilemma in the PNS axon help in the regeneration of the neuron. • Regions of the nervous system containing groupings of myelinated axons make up the “white matter” • “gray matter” is mainly comprised of groups of neuron cell bodies, dendrites & synapses (connections between neurons) By Dr. Jeevan Kumar Giri

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Unmyelinated: • Axon does not spirally invaginate into the cytoplasm of Schwan cell. • Multiple axon may invaginate in single Schwan cell. • Travel along the axolemma. • E.g. numerous in dorsal nerve roots and in cutaneous nerve • Post ganglionic nerve fiber of ANS

By Dr. Jeevan Kumar Giri

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Functional classification  Sensory/afferent neurons –carry impulse from the receptor organ to the CNS Primary sensory: − cell body lies outside the CNS. – First-order neurons conduct impulses from receptors of the skin and from proprioceptors (receptors located in a join, muscle or tendon) to the spinal cord or brain stem, where they synapse with second-order neurons. First-order neuron’s cell bodes reside in ganglion (dorsal root or cranial). – Eg: spinal nerve. 1st order neuron

By Dr. Jeevan Kumar Giri

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Secondary sensory: cell body lies inside the CNS. Eg: mesencephalic nucleus of 5th cranial nerve. 2nd order neuron Tertiary sensory: the cell body lies in the thalamus. 3rd order neuron.

By Dr. Jeevan Kumar Giri

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 Inter neurons: • Communication neurons, that connect the motor and sensory neurons. It lies in the spinal cord. • Forms the pathway for reflex arc. • Involuntary action By Dr. Jeevan Kumar Giri

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Motor/Efferent neurons:  Upper motor neurons:  The cell body is located in the motor cortex of cerebrum.  Forms the descending pathway of the bran and synapse with the motor neuron of cranial nerve nucleus in the brain stem and also to motor neuron of the spinal nerve in ant. Horn of spinal cord.  Involves in voluntary control of muscle By Dr. Jeevan Kumar Giri activity.

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 Lower motor neurons:  they have cell body in brain stem and spinal cord.  Motor neuron of the anterior horn in spinal and motor nuclei of the cranial nerve.

By Dr. Jeevan Kumar Giri

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 In ANS motor neuron are of 2 types:  Preganglionic neuron: cell body lies within brain and spinal cord.  Post ganglionic neuron: cell body lies outside the CNS i.e. bilateral, collateral and terminal ganglion.

By Dr. Jeevan Kumar Giri

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On the basis of diameter and velocity of conduction I. Type A     

Fast conduction fiber Has both motor and sensory function Velocity 12-120m/s Diameter 2 to 20 micrometer Further divided in to Aα, Aβ, Aγ & Aδ

By Dr. Jeevan Kumar Giri

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Type

Sub type

Efferent

Type A fibers

α

• Extrafusal muscle fibers

Afferent • Encapsulated receptor of skin, joints, GUT • Primary sensory fibers from muscle spindles Gr.I • Secondary sensory fibers from muscle spindles Gr. II. • Muscle spindle -Touch and pressure

β γ

• Intrafusal fibers of muscle spindles

δ

• Are collateral of Aα that innervate the some intrafusal also.

• Thermorecepters and nociceptors. Gr. III

By Dr. Jeevan Kumar Giri

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II. Type B conduction velocity 3-15m/s Diameter 1-5 micro meter Myelinated Preganglionic autonomic efferent Afferent fibers from skin or viscera Free nerve ending in connective tissue of muscles Gr. III

By Dr. Jeevan Kumar Giri

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III. Type C Conduction velocity: 0.5-2m/s Diameter: 0.2-1.5 micrometer Unmyelinated Postganglionic autonomic fibers Nociceptive fibers from connective tissue. Gr.IV

By Dr. Jeevan Kumar Giri

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By Dr. Jeevan Kumar Giri

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The Synapse • Junction between neuron. • between receptor and neuron or between neuron and effector. • Site where action potentials in one cell cause action potentials in another cell.

• Synapses are of 2 types – Chemical synapse. – Electrical synapse By Dr. Jeevan Kumar Giri

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Electrical synapse • The one cell may excite another without there release of the neurotransmitter. • At such site adjacent cell have direct channels of communication through which ions can pass from one cell to another altering their electrical status. • The connexin protein lies in between the gap junction of two adjacent cell that create the small open channels between the cell. • Present in lower vertebrates and invertebrates. • Between the myocytes. Atypical synapse By Dr. Jeevan Kumar Giri

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Chemical synapse  A chemical synapse produces only one-way information transfer-from a pre synaptic neuron to a postsynaptic neuron.  Involve the release of neurotransmitters.  They are typical synapse

By Dr. Jeevan Kumar Giri

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Classification of the synapse based on neuronal element involved. • Axodendritic: commonest type of synapse. • Axosomatic synapse: • Asoaxonal synapse:

• Dendroaxonic synapse: • Dendrodendritic synapse: • Somatosomatic synapse: • Somatodendritic synapse:

By Dr. Jeevan Kumar Giri

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Chemical Synapses • Components – Presynaptic terminal – Synaptic cleft -20-30nm – Postsynaptic membrane

• Neurotransmitters released by action potentials in presynaptic terminal – Synaptic vesicles – Diffusion – Postsynaptic membrane

• Neurotransmitter removal By Dr. Jeevan Kumar Giri

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• Cytoplasmic thickening of the post synaptic membrane forms the sub synaptic web. • When post synaptic • When pre and post web is thicker and synaptic membrane denser than pre are thin synaptic web • symmetrical or type II • Asymmetrical or type synapse I synapse • It is inhibitory • It is excitatory

By Dr. Jeevan Kumar Giri

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Neuroglia  Neuroglia are the supporting cells of the NS .  They are non-excitable.  They undergo mitotic division.  They take active part in metabolism  They take active part in ionic transport.  They form a continuous glial membrane between the blood vessels and neurons.  Neuroglia are ten times more numerous than neurons. By Dr. Jeevan Kumar Giri

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Neuroglia Neuroglia

Neuroglia in the CNS

Astrocytes

Oligodendrocyes

Neuroglia in PNS

Ependymal cells

Protoplasmic astrocytes

Ependymyocytes

Fibrous astrocytes

Choroid epithelial cells

Microglia

Satellite cells or capsular cells

Schwann cells or neurolemmocytes

Tanycytes

11-43 By Dr. Jeevan Kumar Giri

Classification of Neuroglia Morphological classification: 1) Macroglia • Astrocytes • Oligodendrocyes & Schwann cell • Ependymal cells 2) Microglia

According to location CNS Astrocytes, Oligodendrocyes, Mircoglia, Ependymal cells PNS • Schwann cells • Satellite cells By Dr. Jeevan Kumar Giri

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Astrocytes •

• •



largest and have a stellate (star-shaped) appearance because their processes extend in all directions. Their nuclei are ovoid and centrally located. The astrocytes provide support for the neurons, a barrier against the spread of transmitters from synapses, and insulation to prevent electrical activity of one neuron from affecting the activity of a neighboring neuron. Some transmitters (for example, glutamate and γ-aminobutyric acid [GABA]), when released from nerve terminals in the CNS, are taken up by astrocytes, thus terminating their action •

Fx: mechanical supports, insulator, BBB, absorption of NT.

By Dr. Jeevan Kumar Giri

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Types: – Fibrous –seen in white matter, thin and asymmetrical process – Fibrous astrocytes function to repair damaged tissue, and this process may result in scar formation. – Protoplasmic –gray mater, process are thick and symmetrical – They give out thicker and shorter processes, which branch profusely. Several of their processes terminate in expansions called end-feet – serve as metabolic intermediaries for neurons – Intermediate –between above two. • Muller Cells –Modified astrocytes, Muller cells are present in the retina.

By Dr. Jeevan Kumar Giri

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• The neuronal cell bodies, dendrites, and some axons are covered with end-feet of the astrocytes.

BBB

• The end-feet join together to form a limiting membrane on the inner surface of the pia mater (glial limiting membrane) and outer surface of blood vessels (called perivascular lining membrane)



The perivascular end-feet may serve as passageways for the transfer of nutrients from the blood vessels to the neurons. • Protoplasmic astrocytes on the capillaries as perivascular end-feet is one of the anatomical features of the blood-brain barrier.

By Dr. Jeevan Kumar Giri

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Oligodendrocyes& Schwann cell • Rounded, pear shaped • Form myelin sheath of the CNS axon & PNS axon • Schwann cell ensheath only one axon • Oligodendrocyes may enclose several axon. By Dr. Jeevan Kumar Giri

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Ependymal cell • Line the ventricles of brain and central canal of spinal cord • Types: – Ependymocytes –numerous – Choroidal epithelial cells – Tanycytes

By Dr. Jeevan Kumar Giri

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• Ependymocytes – Numerous – Lines the ventricles and central canal of spinal cord.

By Dr. Jeevan Kumar Giri

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• Choroidal epithelial cells – – – – –

Cover the choroid plexus Ciliated Metabolically active Tight junction Forms the blood CSF barrier

By Dr. Jeevan Kumar Giri

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Choroid plexus • Modified ependymal cells –Choroidal epithelial cells. • 4 choroid plexuses in brain, one in each of the ventricles • Choroid plexuses consist of layer of ciliated cuboidal epithelial cells that surround a core of capillaries and loose connective tissue.

By Dr. Jeevan Kumar Giri

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• Tanycytes  They special ependymal cells found in the 3rd ventricle of the brain, and on the floor of the 4th ventricle  They have processes extending deep into the hypothalamus.  Tanycytes have been implicated in the transport of hormones from the CSF to capillaries of portal system and from hypothalamic neurons to the CSF

4th ventricle

By Dr. Jeevan Kumar Giri

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Microglia • Smallest of all. Macrophage of NS. • Flattened cell body with short process • Seen in the capillaries – element of blood –derived from monocytes they invade in the brain during fetal life. • Numerous in gray matter than white. • Fx: phagocyte. By Dr. Jeevan Kumar Giri

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Satellite cells • Capsular cells • Surround neuron cell bodies in ganglia, provide support and nutrients

By Dr. Jeevan Kumar Giri

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Applied anatomy 1) Spread of Diseases through Axonal transport. A. Rabies –It affect the dorsal horn of the spinal cord (Rabies is caused by lyssaviruses). B. Herpes simplex –HSV C. Herpes Zoster –spread of it is on the basis of dermatomes. varicella-zoster virus (VZV) that has remained dormant within dorsal root ganglia, results in herpes zoster (shingles). D. Poliomyelitis –destroying motor neurons within the spinal cord, brain stem, or motor cortex. This leads to the development of paralytic poliomyelitis

By Dr. Jeevan Kumar Giri

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2)Tumors of Neurons a) Neuroblastoma – – – – –

It is a type of cancer that forms in certain types of nerve tissue (tumer of neuroblast). It most frequently starts from one of the adrenal gland, but can also develop in the neck chest abdomen or spine. Symptoms may include bone pain, a lump in the abdomen, neck, or chest, or a painless bluish lump under the skin. Occasionally neuroblastoma may be due to a mutation, inherited from parents common in children up to 5years of age.

By Dr. Jeevan Kumar Giri

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b) Ganglioneuroma  Ganglioneuroma is a rare and benign tumer of the autonomic nerve fiber arising from neural crest sympathogonia which are completely undifferentiated cells of the sympathetic nervous system.  common locations include the adrenal gland, paraspinal, retroperitoneum, posterior mediastinum, head, and neck

c) Pheochromocytoma  Pheochromocytoma (PCC) is a neuroendocrine tumor of the medulla of the adrenal glands (originating in the chromaffin cells), or extra-adrenal chromaffin tissue that failed to involute after birth, that secretes high amounts of catecholamines  The signs and symptoms of a Pheochromocytoma are those of sympathetic nervous system hyperactivity

By Dr. Jeevan Kumar Giri

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3) Neoplasms of Neuroglia a) Gliomas  A glioma is a type of tumor that starts in the glial cells of the brain or the spine. Gliomas comprise about 30 per cent of all brain tumors and central nervous system tumors, and 80 per cent of all malignant brain tumors.  Ependymomas: ependymal cells  Astrocytomas: astrocytes (glioblastoma multiforme is a malignant astrocytoma and the most common primary brain tumor among adults).  Oligodendrogliomas: oligodendrocytes  Brainstem glioma: develop in the brain stem  Optic nerve glioma: develop in or around the optic nerve  Mixed gliomas, such as oligoastrocytomas, contain cells from different types of glia

By Dr. Jeevan Kumar Giri

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b) Glioblastoma  It is the commonest of all malignant tumors of the brain.  In fact, it is found to be highly cancerous containing a very high blood supply and comprising of dead tissue and cystic tissue.  Due to its multiple forms, it is also termed Glioblastoma multiforme (GBM).  It arises from star shaped cells in the brain called astrocytes. The grade IV type of tumor arising from these astrocytes which is infiltrative and undifferentiated from other normal cells is called Glioblastoma.

By Dr. Jeevan Kumar Giri

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4) Multiple Sclerosis  It is a demyelinating disease  immune system attacks the protective sheath (myelin) that covers nerve fibers and causes communication problems between your brain and the rest of your body.  This damage disrupts the ability of parts of the nervous system to communicate  signs and symptoms include physical, mental, and sometimes psychiatric problems

By Dr. Jeevan Kumar Giri

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Reference 1. 2. 3. 4. 5.

Text book of human neurology by Inderbir Singh Grays anatomy Essentials of human antomy –Neuroantomy by A.K Datta. Text book of human Histology by Inderbir Singh. Human Neuroanatomy by Vishram singh.

By Dr. Jeevan Kumar Giri

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