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Nervous system by Dr Chaman Lal (CK)

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Nervous System, types of neurons, synapses, blood brain barriers..etc

Nervous System, types of neurons, synapses, blood brain barriers..etc

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  • 1. Federal Institute of Health Sciences Multan By: Chaman Lal B.S.PT, DPT, Dip. in sports Injuries, MPPS(PAK), PG in Clinical Electroneurophysiology (AKUH), Registered.EEGT (USA), Member of AANEM & ASET (USA).
  • 2. Study Outlines  Introduction to Nervous System  Classification of Nervous System  Cells Types of Nervous System  Functions of different types of cells  Blood Brain Barriers  Neuromuscular Junction (Synapse) & Its Types  Reflex Arc & its components 1/9/2014 Nervous System By: CK (FIHS) 2
  • 3. Introduction to Nervous System Nervous system is the chief controlling and coordinating system of the body. It controls & regulates all activities of the body, weather voluntary or involuntary. It adjusts the individuals to given surroundings. Its based on -Sensitivity, -Conductivity & -Responsiveness 1/9/2014 Nervous System By: CK (FIHS) 3
  • 4. Classification Of Nervous System CONTROL SYSTEMS There are two main control systems in your body. 1. Nervous system – which has two main sections, 1. Central Nervous System (CNS) 1. 2. Peripheral Nervous System (PNS) 2. Endocrine system – which is a system of glands that release a number of signalling chemicals known as hormones. 1/9/2014 Nervous System By: CK (FIHS) 4
  • 5. Anatomical Divisions of Nervous System  Central Nervous System (CNS)  Brain  Spinal Cord  Peripheral Nervous System (PNS)  Spinal Nerves & Plexus  Cranial Nerves  Peripheral Nerves
  • 6. MNEMONIC             1/9/2014 OLFACTORY OPTIC OCULOMOTOR TROCHLEAR TRIGEMINAL ABDUCENS FACIAL VESTIBULOCOCHLEAR GLOSSOPHARYNGEAL VAGUS ACCESSORY HYPOGLOSSAL Nervous System By: CK (FIHS)            OH ONCE ONE TAKES THE ANATOMY FINAL VERY GOOD VACATION A-HEAD 6
  • 7. NERVOUS SYSTEM CNS Nervous system releases electrical impulses that are quick but the effects are short lived and it involves the CNS (either just spinal cord or both spinal cord and brain) messages are carried by neurons PNS ANS SNS Parasympathetic Sympathetic 1/9/2014 Nervous System By: CK (FIHS) 7
  • 8. Classification of NS…cont’d  Central or CNS that is made up of the spinal cord and brain and functions to coordinate all actions of the body  Peripheral or PNS that is made up of the bodies nerves and functions to connect the CNS to the rest of the body through neurones. do require a fast response (rest and digest response) 1/9/2014 Nervous System By: CK (FIHS) 8
  • 9. Functional Divisions Of Nervous System  Afferent  Efferent  Somatic  Autonomic   1/9/2014 Sympathetic Parasympathetic Nervous System By: CK (FIHS) 9
  • 10. Functional Divisions Of Nervous System Central Nervous System Brain Spinal Cord Sensor Division (afferent) Peripheral Nervous System Cranial Nerves Spinal Nerves Motor Division (efferent) Autonomic Nervous System (involuntary) Somatic Nervous System (voluntary)
  • 11. Classification of NS…cont’d PNS is further divided into:  Somatic or SNS which is associated with the voluntary control of body movements and is made up of all neurones, sense organs, skin, skeletal muscles  Autonomic or ANS which is associated with the involuntary control of body movements such as reflex and controls such things as heart rate, body temperature, digestion etc.  The ANS is further divided into :  Parasympathetic nervous system works in actions that do not require a fast response e.g rest & Digest etc  Sympathetic nervous system works in actions that do require fast response. e.g Fight & Freight etc 1/9/2014 Nervous System By: CK (FIHS) 11
  • 12. Name Description Important named parts Telencephalon (Cerebral Cortex & cerebrum). Forebrain Prosencephalon Largest part of the brain. Basal Ganglia Diencephalon (thalamus, hypothalamus, pineal body) Midbrain Mesencephalon (brain stem) 1.5 cm in length. cerebral peduncles. Pons. Hindbrain Rhombencephalon (brain stem) 1/9/2014 Quadrigeminal bodies Medulla oblongata. Cerebellum. Nervous System By: CK (FIHS) 12
  • 13. Parts of the nervous system For example; If you smell something burning…  Your nose (receptor) detects the stimulus (smell)  Nerve fibres send the message to the brain  Your brain then sends a message to move your body away or to put out the fire! 1/9/2014 Nervous System By: CK (FIHS) 13
  • 14. RECEPTORS  Receptors are sensors on the body that detect stimuli  They convert stimuli into (messages) called impulses. 1/9/2014 Nervous System By: CK (FIHS) electrical signals 14
  • 15. EFFECTORS An effector is any part of the body that produces the response. Here are some examples of effectors:  a muscle contracting to move the arm  a muscle squeezing saliva from the salivary gland  a gland releasing a hormone into the blood 1/9/2014 Nervous System By: CK (FIHS) 15
  • 16. Cell Types of Nervous System  Nervous System is composed of two distinct types of cells. a. Excitable Cells: These are the nerve cells or neurons. b. Non-excitable Cells:These cells constitute neurologlia and ependyma in the CNS, & schwann cells in the PNS. 1/9/2014 Nervous System By: CK (FIHS) 16
  • 17. a. NERVE FIBRES  Nerve fibres are bundles of nerve cells (neurons) that pass on electrical signals (impulses) to the brain.  From the brain, nerve fibres send impulses to effectors (muscles). 1/9/2014 Nervous System By: CK (FIHS) 17
  • 18. Neuron: It has a cell body or soma or PERIKARYON, with nucleus in center and nissl granules in its cytoplasm.  It has cell processes called “nenrites” which are of two types. Many short afferent processes, which are freely branching and varicose are called “Dendrites”.  A single long efferent process, which may give off occasional branches (collateral) and is of uniform diameter, is called “Axon”. 1/9/2014 Nervous System By: CK (FIHS) 18
  • 19. 1/9/2014 Nervous System By: CK (FIHS) 19
  • 20. Neuron: The terminal branches of the axon are called axon terminals, axon knobs, axon telodendria, or axon button.  The cell bodies (somata) of the neurons form grey matter and nuclei in the CNS, and ganglia in the PNS.  The cell processes (axons) form tracts ion the CNS, & nerves in the PNS.  Schwann cells form sheaths for axons of PNS while oligodendrocytes form sheath in CNS. 1/9/2014 Nervous System By: CK (FIHS) 20
  • 21. Neurons and neuroglial cells  Axon in peripheral nervous system with myelin sheath formed by Schwann cells  Provides for insulation and allows for saltatory propagation of action potentials 1/9/2014 Nervous System By: CK (FIHS) 21
  • 22. Saltatory conduction and role of Schwann cells 1/9/2014 Nervous System By: CK (FIHS) 22
  • 23. TYPES OF NEURONS  Neurons can be classified in several ways.  According to their,  1.Number of their processes (Neurites)  2.Length of their axon  3.Function  According to Number of Processes:-  A.Unipolar  Mesencephalic nucleus  B. Psudo-unipolar  Sensory ganglia  C. Bipolar  Spiral & vestibular ganglia  D. Multipolar  The most common types 1/9/2014 Nervous System By: CK (FIHS) 23
  • 24. 1/9/2014 Nervous System By: CK (FIHS) 24
  • 25. 2. According to Length of Neuron: Golgi Type-I Neuron:- With a long axon &  Golgi Type-II Neuron:also called microneurons, with a short or no axon (anaxonic neuron). 1/9/2014 Nervous System By: CK (FIHS) 25
  • 26. 1/9/2014 Nervous System By: CK (FIHS) 26
  • 27. 3. According to Functions of neurons:There are three types of neurons according to their function; 1. Sensory neuron – carries impulses from the receptors to the spinal cord. 2. Relay Neuron – carries impulses to and from the spinal cord and the brain 3. Motor Neuron – carries impulses from the brain to the effector. 1/9/2014 Nervous System By: CK (FIHS) 27
  • 28. Types of Neurons--structural classes
  • 29. 1/9/2014 Nervous System By: CK (FIHS) 29
  • 30. Important Points:The average human brain has about 100 billion neurons (or nerve cells) and an equal or slightly greater number of neuroglia (or glial cells) which serve to support and protect the neurons. Each neuron may be connected to up to 10,000 other neurons, passing signals to each other via as many as 1,000 trillion synaptic connections, equivalent by some estimates to a computer with a 1 trillion bit per second processor. 1/9/2014 Nervous System By: CK (FIHS) 30
  • 31. b.Neuroglial cells in CNS  The non-excitable cells of the NS form a major component of nervous tissues. These include :  1. Neurologlial Cells: found in the parenchyma of brain and spinal cord.  2. Ependymal Cell: Lining the internal cavities.  3. Capsular or Satellite Cells: Surrounding neurons of the sensory and autonomic ganglia.  4. Schwann Cells: forming sheaths for axons of peripheral nerves.  5. Several types of supporting cells: ensheathing the motor and sensory nerves terminals and supporting the sensory epithelia. 1/9/2014 Nervous System By: CK (FIHS) 31
  • 32. b.Neuroglial cells in CNS…cont’d The Neuroglial cells found in the parenchyma of brain and spinal cord are broadly classified as;  A. Macroglia:Theses are; a. Astrocytes b. Oligodendrocytes & c. Glioblasts  B. 1/9/2014 Microglia Nervous System By: CK (FIHS) 32
  • 33. Nervous Tissue: Support Cells (Neuroglia or Glia) A. Astrocytes:Abundant, star-shaped cells. These are of two types: 1.Protoplasmic Astrocytes: Have thick and symmetrical processes and found in grey matter. 2.Fibrous Astrocytes: Have thin and asymmetrical processes and found in white matter. The processes of astrocytes often end in plate-like expansions on the blood vessels, ependyma , & pial surface of the CNS. These form barrier between capillaries & neurons. Control the chemical environment of the brain (CNS). 1/9/2014 Nervous System By: CK (FIHS) 33
  • 34. 1/9/2014 Nervous System By: CK (FIHS) 34
  • 35. Nervous Tissue: Support Cells….cont’d B. Oligodendrocytes(CNS): These have fever cell processes. These are of two types; 1. Intrafasicular Cells:- These cells are found in the myelinated tracts, 2.Perineuronal Cells:- These are present on the surface of the somata of neurons. These produce myelin sheath around nerve fibers in the central nervous system.
  • 36. Nervous Tissue: Support Cells….cont’d  C. Glioblasts:These are stem cells which can be differentiate into macroglial cells. They are particularly numerous beneath the ependyma. B. Microglia:  These are smallest of the glial cells. These have flattened cell body with a few short, fine processes.  Monitor health of neurons and transform into immune macrophages (normal immune cells have no access to CNS).  These are Spider-like and are phagocytic in nature.  These dispose of debris  Microglial cells are possibly derived from the circulating monocytes which migrate cells are possibly derived from the circulating monocytes which migrate into the CNS during the late foetal and early postnatal life. 1/9/2014 Nervous System By: CK (FIHS) 36
  • 37. Nervous Tissue: Support Cells….cont’d 2. Ependymal cells (CNS):  These Line the cavities of the brain and spinal cord  Cilia beat to move or circulate cerebrospinal fluid (CSF).  These form barrier between CFS and tissue fluid. 3. Satellite cells: These surround the neurons of sensory & autonomic ganglia. These protect neuron cell bodies. 4. Schwann cells (PNS): Form myelin sheath in the peripheral nervous system. 1/9/2014 Nervous System By: CK (FIHS) 37
  • 38. Neuroglial cells in CNS 1/9/2014 Nervous System By: CK (FIHS) 38
  • 39. Functions of Glial & Ependymal Cells 1) These provide mechanical support to neurons. 2) As non-conducting nature these act as insulators between the neurons & prevent neuronal impulses from spreading in unwanted directions. 3) By phagocytosis they help to engulf the foreign material and removal of debris. 4) Help to repair the damaged area of nervous tissue. By proliferation (gliosis) they form glial scar tissue, and fill the gaps left by degenerated neurons. 5) Glial cells can take up and store neurotransmitters released by the neighboring synapses. These can either be metabolized or released again from the glial cells. 1/9/2014 Nervous System By: CK (FIHS) 39
  • 40. Functions of Glial & Ependymal Cells….cont’d 6. They help in neuronal functions by maintaining 7. 8. 9. 10. a suitable metabolic and ionic environment for the neuron. Oligodendrocytes myelinate tracts in CNS and schwann cell myelinate the nerves in PNS. Ependymal cells are concerned with exchanges of materials between brain and CSF. The role of glial cells in the nutrition of nerve cells is claimed since long but is not confirmed. These act as blood brain barrier. 1/9/2014 Nervous System By: CK (FIHS) 40
  • 41. Blood Brain Barrier • Composed of specialized endothelial cells which form tight intercellular junctions which selectively pass the substances across the brain tissue. Formation of junctions is dependent on: Cytokines or factors derived from astrocytes The nature of the extracellular matrix • These have few pinocytotic vesicles. • There are greater number of mitochondria per unit cell present than occur in other endothelial cells. 1/9/2014 Nervous System By: CK (FIHS) 41
  • 42. Blood Brain Barrier……cont’d  The possible Structures constituting the blood brain barrier are:  A). Capillary endothelium without fenestrations  B). Basement membrane of the endothelium  C). The end feet of astrocytes covering the capillary walls. The barrier permits a selective passage of blood contents to the nervous tissue, and thus the toxic and harmful substances are ordinarily prevented from reaching the brain. 1/9/2014 Nervous System By: CK (FIHS) 42
  • 43. Nervous System By: CK (FIHS) 1/9/2014 43
  • 44. Reflex Arc  A reflex arc is the basic functional unit of the system, which can perform an integrated neural activity. In its simplest form (monosynaptic reflex arc). It is made up of;  1). A Receptor e.g., skin  2). A sensory or afferent neuron  3). A interneuron (inter communicating neuron)  4). A motor or efferent neuron &  5). An effector, e.g. Muscle The complex forms of reflex are polysynaptic due to addition of one or more interneuron in between the afferent and efferent neurons. An involuntary motor response of the body called a reflex action. 1/9/2014 Nervous System By: CK (FIHS) 44
  • 45. The Reflex Arc 1/9/2014 Nervous System By: CK (FIHS) 45
  • 46. The Reflex Arc Reflex – rapid, predictable, and involuntary responses to stimuli Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector 1/9/2014 Nervous System By: CK (FIHS) 46
  • 47. Simple Reflex Arc 1/9/2014 Nervous System By: CK (FIHS) 47
  • 48. 1/9/2014 Nervous System By: CK (FIHS) 48
  • 49. Synapse  It is the functional junction gap along with the impulses are conducted in different directions, each junction between the neurons is called a “synapse”.  Impulse is transmitted across a synapse by specific neurotransmitters like acetylcholine, catecholamines (noradrenalin & dopamine), serotonin, histamine, glycine, GABA, and certain polypeptides.  Types of Synapses are: 1. Axo-dendritic, 2. Somato-somatic 3. Somato-dendritic 4. Serial in Nature Functionally, a synapse may be inhibitory or excitatory. 1/9/2014 Nervous System By: CK (FIHS) 49
  • 50. Synapse 1/9/2014 Neuro-muscular junction is synapse between motor unit and muscle cell (motor unit). Nervous System By: CK (FIHS) 50
  • 51. 1/9/2014 Nervous System By: CK (FIHS) 51
  • 52. Classification of Peripheral Nerve Fibers  A . According to their Function: 1.Somatic efferent:- to supply striated muscles of somatic origin.  2.General Visceral efferent:- to supply smooth muscles and      glands. 3.Special Visceral efferent (branchial efferent):- to supply striated muscles of branchial origin. 4.General Somatic afferent:_ to carry exteroceptive impulses from the skin, and proprioceptive impulses from the muscles, tendons and joints. 5.General Visceral afferent:- to carry visceroceptive impulses (like pain) from the viscera. 6.Special Visceral Afferent:- to carry the sensation of taste, & 7.Special somatic afferent: to carry the sensations of smell, vision, hearing and equilibrium. 1/9/2014 Nervous System By: CK (FIHS) 52
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  • 57. Classification of Peripheral Nerve Fibers  B. According to their size & speed of conduction:- 1. Group-A fibers:- (Thickest & fastest) -These are myelinated neurons having diameter of 1.522 microns. - Their conduction speed is 4-120 meters per second. - e.g. skeletomotor fibers (alpha A), fusimotor fibers (beta A & gamma A), and afferent fibers to skin, muscles & tendons. 2. Group-B fibers:- (Medium size and speed) -These myelinated and have diameter of 1.5-3 microns. -Their conduction speed is 3-15 meters per second. -e.g., Preganglionic autonomic efferents. 1/9/2014 Nervous System By: CK (FIHS) 57
  • 58. Classification of Peripheral Nerve Fibers….cont’d 3. Group-C fibers:- (Thinnest and slowest). - These are non-myelinated have the diameter of 0.1-2 microns. -Their conduction speed is 0.5-4 meters per second. -e.g., Postganglionic autonomic efferents, and afferent fibers to skin, muscles and viscera. -The same efferents with a conduction speed and myelination similar to B fibers are called delta-A fibers. -Thus the fiber diameter is directly proportional to conduction velocity; the velocity (in meters per second) is approximately six times the diameters (in microns). 1/9/2014 Nervous System By: CK (FIHS) 58
  • 59. “Horns” In The Spinal Cord  In the spinal cord the gray matter is present inside and white matter is towards outside while in brain this distribution is vice versa.  On cross section of the spinal cord gray matter in spinal cord presents butterfly like structure form which some projections like “Horns” are seen termed as: Ventral/Anterior Horn→ {Ventral/Anterior/Motor Root Centre} Lateral Horn →{Preganglionic Sympathetic Neurons; its present only in T1-L2} Dorsal/Posterior Horn→{Dorsal/Posterior/Sensory Root Centre} 59
  • 60. Terms To define….cont’d  Root • Ventral/Anterior/Motor/Efferent Root: It arises from Ventral or Anterior horn of the Spinal Cord and carries only motor fibers. • Dorsal/Posterior/Sensory/Afferent Root: It arises from Dorsal or Posterior horn of the Spinal Cord and carries only sensory fibers. Spinal Nerve: • The dorsal and ventral roots, arising from each spinal cord segment, fuse within the intervertebral foramen to form a mixed spinal nerve. 1/9/2014 Nervous System By: CK (FIHS) 60
  • 61. 1/9/2014 Nervous System By: CK (FIHS) 61
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  • 63. Terms To define….cont’d Collection of the nerve cell bodies is called “Ganglion” e.g., Dorsal Root Ganglion “DRG”, sympathetic paravertebral ganglion.  Ganglion:  Ramus (Pl. rami) The spinal nerve when exits from the vertebrae it divides into two branches termed as; 1. Ventral/Anterior Primary Ramus 2. Dorsal/Posterior Primary Ramus • Ventral/Anterior Ramus: It is the ventral or anterior division of the spinal nerve out side the vertebrae. It supplies to the skin, muscles on anterior body & viscera etc. • Dorsal/Posterior Ramus: It is the dorsal or posterior division of the spinal nerve out side the vertebrae. It supplies to the skin & muscles of the back. 1/9/2014 Nervous System By: CK (FIHS) 63
  • 64. 1/9/2014 Nervous System By: CK (FIHS) 64
  • 65. Spinal Nerves  31 pairs spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal nerve.  Formation: each spinal nerve is formed by union of anterior and posterior roots at intervertebral foramen  The anterior root - contains motor fibers for skeletal muscles. Those from T1 to L2 contain sympathetic fibers; S2 to S4 also contain parasympathetic fibers.  The posterior root-contains sensory fibers whose cell bodies are in the spinal ganglion. 1/9/2014 Nervous System By: CK (FIHS) 65
  • 66. Spinal Nervers 1/9/2014 Nervous System By: CK (FIHS) 66
  • 67. Nerve Structure: The whole nerve trunk is ensheathed by PINEURIUM.  Each fasciculus by PERINEURIUM.  Each nerve fiber by a delicate ENDONEURIUM.  The toughness of a nerve is due to its fibrous sheaths, otherwise the nerve tissue itself is very delicate and friable. 1/9/2014 Nervous System By: CK (FIHS) 67
  • 68. Nerve Fibers  Large axons are covered by a myelin sheath and termed myelinated or medullated fibers. (white matter as in CNS).  Thinner axons of less than one micron diameter do not have the myelin sheath are therefore termed as nonmyelinated or non-medullated fibers (grey fibers).  However, all the fibers whether myelinated or nonmyelinated have neurolemmal sheath, which is uniformly absent in the tracts. In peripheral nerves, both the myelin and neurolemmal sheaths are derived from schwann cells. 1/9/2014 Nervous System By: CK (FIHS) 68
  • 69. Myelinated Fibers  Myelinated fibers form the bulk of the somatic nerves.  Structurally, they are made up of following parts from within outwards.  1. Axis Cylinder forms the central core of the fiber. It consists of axoplasm covered by axolemma.  2. Myelin sheath, derived from Schwann cells, surrounds the axis cylinder. It is made up of alternate concentric layers of lipids and proteins formed by spiralization of the mesxaon: the lipids include cholesterol, gylcolipids and phospholipids.  The myelin sheath is interrupted at regular intervals called the node of Ranvier where adjacent schwann cell meet. 1/9/2014 Nervous System By: CK (FIHS) 69
  • 70. Myelinated Fibers cont’d. . .  Thicker axons posses a thicker coat of myelin and longer internodes.  Each internode is myelinated by one schwann cell.  Myelin can also show localized areas of incomplete fusion of the Schwann cell membrane. Oblique clefts in the myelin, called incisures of Schmidt Lanterman, provide conduction channels for metabolites into the depth of myelin and to the subjacent axon. These areas (or incisures)may be found trapped between membranes.  Myelin sheath acts as an insulator for the nerve fibers. 1/9/2014 Nervous System By: CK (FIHS) 70
  • 71. Myelinated Fibers cont’d. . . 3. Neurolemmal Sheath (Sheath of Schwann) surrounds the myelin sheath. It presents the plasma membrane. (basal lamina) of the Schwann cell. Beneath the membrane there lies a thin layer of cytoplasm with the nucleus of the schwann cell. The sheaths of two cells interdigitate at the node of ranvier. 4. Endoneurium, is a delicate connective tissue sheath which surrounds the neurolemmal sheath. 1/9/2014 Nervous System By: CK (FIHS) 71
  • 72.  mesaxon /mes·ax·on/ (mes-ak´son) a pair of parallel membranes marking the line of edge-to-edge contact of Schwann cells encircling an axon. 1/9/2014 Nervous System By: CK (FIHS) 72
  • 73. 1/9/2014 Nervous System By: CK (FIHS) 73
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  • 75. Myelinated Fibers cont’d. . .  Neurolemmal sheath is necessary for regeneration of a damaged nerve.  Tracts do not regenerate because absence of neuroloemma.  Endoneurium is a delicate connective tissue sheath which surrounds the neurolemmal sheath. Non-myelinated fibers  Consist of smaller axons of the CNS, in addition to peripheral postganglionic autonomic fibers, several types of fine sensory fibers (C fibers of skin, muscles and viscera), olfactory nerves etc.  Structurally, a non-myelinated “fiber” consists of groups of axons (0.12-2 microns diameter) that have invaginated 1/9/2014 Nervous System By: CK (FIHS) 75
  • 76. Non-myelinated fibers…cont’d  Separately a single schwann cell (in series) without any spiraling of the mesaxon.  The endoneurium , instead of ensheathing individual axons, surrounds all the neurolemmal sheath by virtue of which of the non-myelinated fibers, like the myelinated fibers, can regenerate after damage. 1/9/2014 Nervous System By: CK (FIHS) 76
  • 77. Degeneration & Regeneration of Neurons  If nerve (axon) is injured or cut a series of degenerative and than regenerative changes follow.  Degeneration is of two type; 1. Retrograde degeneration: Degenerative changes in the neurons that occur in proximal part to injury. 2. Antegrade degeneration: Degenerative changes in the distal part to site of injury. a. The cell bodies undergo chromatolysis with in 48 hours of injury. The cell becomes swollen and rounded, nucleus is pushed to the periphery, and the nissl granules disintegrate and disappear. b. The proximal part of the axon survives if the mother cells do not die. Only a small segment near the cut end degenerates in a way similar to the distal part. 1/9/2014 Nervous System By: CK (FIHS) 77
  • 78. Degeneration & Regeneration of Neurons….cont’d c. A the site of injury, the schwann cells proliferate more actively in the distal part than in the proximal, in an attempt to fill the gap. Gaps up to 3cm may be bridged in this way. Bridging can be facilitated by stitching the two parts. However, in wider gaps nerve grafts may be tried. d. The distal part of the axons undergoes Wallerian (antegrade) degeneration within a few days of injury. The axis cylinder becomes fragmented and the myelin sheath breaks up into fat droplets. The schwann cell multiply, which on one hand act as macrophages to remove the debris of degenerated axon and myelin, and on the other hand form a large series of membranous (neurolemmal) tubes which play a vital role in regeneration of the nerve fibers. The nucleated cellular cords in the distal part are called bands of Bungner. 1/9/2014 Nervous System By: CK (FIHS) 78
  • 79. Different degrees of Nerve Injury 1/9/2014` Nervous System By: CK (FIHS) 79
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  • 83. Spinal Nerve….cont’d  Dermatome:- An area of skin supplied by a single segment spinal nerve is called dermatome.  Myotome:Group of Muscle fibers supplied by single segment of spinal nerve is called myotome. Nerve Plexuses for Limbs:A network of spinal nerves formed by ventral rami is known as nerve plexuses. Plexus formation is a physiological or functional adaptation, and is perhaps the result of the following special features in the limbs. 1. Overlapping of dermatomes, 2. Overlapping of myotomes, 3. Composite nature of muscles, 4. Possible migration of muscle from the trunk to the limbs & 5. Linkage of the opposite groups of muscles in the spinal cord for reciprocal innervation. 1/9/2014 Nervous System By: CK (FIHS) 83
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  • 85. Blood & Nerve Supply of Peripheral Nerves  The peripheral nerves are supplied by vessels, called vasa nervorum, which form longitudinal anastomoses on the surface of the nerves.  The nerves distributed to the sheaths of the nerve trunks are called nervi-nervorum. Anastomosis:A precapillary of postcapillary communication between neighboring vessels is called as anastomosis. - Circulation through anastomosis is called Collateral Circulation. 1/9/2014 Nervous System By: CK (FIHS) 85
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  • 87. Parasympathetic Nervous System (PNS)  Parasympathetic Nervous System (PNS)  The hypothalamus is the center of the parasympathetic nervous system. It operates through various interconnecting systems and organs. This system is responsible in the “thinking” phase in stressful situations and is called the “Rest and Digest” phase because your body goes back to its normal responses.  It is also known as ‘craniosacral’ outflow because it arises from the brain (mixed with 3rd, 7th, 9th & 10th cranial nerves) and a S 2-4 segments of the spinal cord. Thus it has a cranial and a sacral part.  Parasympathetic nerve endings are cholinergic in natures. 1/9/2014 Nervous System By: CK (FIHS) 87
  • 88. Sympathetic Nervous System (SNS)  This type of the autonomic nervous system is responsible in the distribution of essential nutrients and oxygen to the various parts of the body. This ANS is responsible for “Flight or Fight.” The body has to respond immediately because of the urgency of some situations.  It is also known as ‘thoracolumbar’ outflow because it arises from T1-L2 segments of the spinal cord.  The medullated Preganglionic fibers arise from the lateral column of the spinal cord, emerge through the ventral rami where the white rami are connected to the ganglia of the sympathetic chain. 1/9/2014 Nervous System By: CK (FIHS) 88
  • 89. Sympathetic Nervous System (SNS). . . Cont’d  Sympathetic nerve endings are adrenergic in nature, meaning thereby that noradrenalin is produced for neurotransmission. The only exception to this general rule are the cholinergic sympathetic nerves supplying the sweat glands and skeletal muscle vessels for vasodilatation.  Functionally, sympathetic nerves are vasomotor (vasoconstrictor), sudomotor (scretomotor to sweat glands), and pilomotor (contract the arrector pili and cause erection of hair) in the limbs and body wall.  In addition, sympathetic activity causes dilation of pupil, pale face, dry mouth, tachycardia, rise in blood pressure, inhibition of hollow viscera, and closure of the perinal sphincters.  The blood supply to the sk.m/s, heart & brain is increased. 1/9/2014 Nervous System By: CK (FIHS) 89
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  • 92. Characteristics Parasympathetic Sympathetic Craniosacral outflow: brainstem nuclei of cranial nerves III, VII, IX and X; spinal cord segments S2-S4 Ganglia in Location of ganglia (intramural= terminal) or close to visceral organ served Thoracolumbar outflow: lateral horn of gray matter of spinal cord segments T1-L2 Ganglia within a few cm of CNS: alongside vertebral column (paravertebral ganglia=chain) and anterior to vertebral column (prevertebral ganglia) Relative length of Long preganglionic; pre- and short postganglionic postganglionic fibers Short preganglionic; long postganglionic Origin 1/9/2014 Nervous System By: CK (FIHS) 92
  • 93. Characteristics Parasympathetic Types of nerves ending Nature of Control Metabolic effect 1/9/2014 Sympathetic Cholinergic Adrenergic Discrete and isolated, combat long term emergencies, Wide Spread and diffuse, combat acute emergencies Anabolic (Energy) sparing Catabolic (Energy consuming) Nervous System By: CK (FIHS) 93
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