classification of nerve fibers

about nerve fibers
It is the structural and the functional unit of nervous system.
The human nervous system contains approximate 1012 neurons.
A nerve fiber is a thread like extension of a nerve cell and consists of an axon and myelin sheath (if present) in the nervous system.
In peripheral nervous system it is formed by
schwann’s cell. While in case of central nervous system it is formed by oligodendroglia.
The places ,where myelin sheath is absent are called node of ranvier(2-3µm) and these are present once about 1-3 mm distance along the myelin sheath.
IT PREVENTS LEAKAGE OF IONS BY 5000 FOLDS.
IT INCREASES VELOCITY OF CONDUCTION BY 5-50 FOLDS DUE TO
SALTATORY CONDUCTION i.e. ABOUT 100 m/s IN CASE OF
MYELINATED NERVE FIBERS WHILE IN NONMYELINATED
IT IS ABOUT 0.25 m/s.
SALTATORY CONDUCTION CONSERVES ENERGY BECAUSE ONLY NODES OF RANVIER GET DEPOLARISED.
These are α type motor nerve fibers.
The neurotransmitter released at the neuron endings is acetylcholine(Ach).
It always leads to muscles excitation . Inhibition takes place centrally due to participation of interneurons.
they innervate smooth muscles , cardiac muscles and glands.
Their main work is to maintain homeostasis with the help of autonomic nervous system.
they can lead to either excitation or inhibition of effector organs
Erlanger and Grasser studied the action potential of mixed nerve trunk by means of cathode ray oscilloscope and they obtained the compounded spike. So they divided nerve fibers into 3 groups. They observed that the main cause of difference in nerve fibers is diameter
AS Diameter increases
Velocity of conduction increases.
Magnitude of electrical response increases.
Threshold of excitation decreases.
Duration of response decreases.
Refractory period decreases.

1. C LASSIFICATIO N OF N ERVE F IBER S PRESENTER R AJ N IDHI ROLL NO 119 PARA G2 G.S.V.M. MEDICAL COLLEGE, KANPUR

2. NEURON It is the structural and the functional unit of nervous system. The human nervous system contains approximate 10 12 neurons. RAJ NIDHI 2

3. STRUCTURE OF NEURON RAJ NIDHI 3

4. INTRODUCTION ABOUT NERVE FIBER A nerve fiber is a thread like extension of a nerve cell and consists of an axon and myelin sheath (if present) in the nervous system. RAJ NIDHI 4

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6. Depending upon STRUCTURE 1 RAJ NIDHI 6

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8. MYELIN SHEATH In peripheral nervous system it is formed by schwann’s cell. While in case of central nervous system it is formed by oligodendroglia. + RAJ NIDHI 8

9. MYELIN SHEATH The places ,where myelin sheath is absent are called node of ranvier (2-3µm) and these are present once about 1-3 mm distance along the myelin sheath. FACTS RAJ NIDHI 9

10. IT PREVENTS LEAKAGE OF IONS BY 5000 FOLDS . IT INCREASES VELOCITY OF CONDUCTION BY 5-50 FOLDS DUE TO SALTATORY CONDUCTION i.e. ABOUT 100 m/s IN CASE OF MYELINATED NERVE FIBERS WHILE IN NONMYELINATED IT IS ABOUT 0.25 m/s . SALTATORY CONDUCTION CONSERVES ENERGY BECAUSE ONLY NODES OF RANVIER GET DEPOLARISED. About the myelinsheath RAJ NIDHI 10

11. Depending upon DISTRIBUTION 2 RAJ NIDHI 11

12. RAJ NIDHI 12

13. SOMATIC NERVE FIBERS These are α type motor nerve fibers. The neurotransmitter released at the neuron endings is acetylcholine(Ach). It always leads to muscles excitation . Inhibition takes place centrally due to participation of interneurons. RAJ NIDHI 13

14. AUTONOMIC NERVE FIBERS they innervate smooth muscles , cardiac muscles and glands. Their main work is to maintain homeostasis with the help of autonomic nervous system. they can lead to either excitation or inhibition of effector organs. RAJ NIDHI 14

15. SYMPATHETIC AND PARASYMPATHETIC NERVE FIBERS PREGANGLIONIC POSTGANGLIONIC Release acetylcholine in both. Release acetylcholine in case of parasympathetic. Release either acetylcholine or norepinephrine in case of sympathetic. Myelinated B fibers. Unmyelinated C fibers are present in the case of sympathetic . Terminate on the postganglionic cyton Terminate on visceral effector. In case of sympathetic it is smaller than postganglionic nerve fiber and vice versa for parasympathetic nerve fiber. In case of parasympathetic it is smaller than preganglionic nerve fiber and vice versa for sympathetic nerve fibre RAJ NIDHI 15

16. 3 Depending upon diameter and velocity of conduction ( Erlanger and Grasser’s classification ) RAJ NIDHI 16

17. ERLANGER AND GRASSER’S CLASSIFICATION Erlanger and Grasser studied the action potential of mixed nerve trunk by means of cathode ray oscilloscope and they obtained the compounded spike. So they divided nerve fibers into 3 groups . They observed that the main cause of difference in nerve fibers is diameter RAJ NIDHI 17

18. PROPERTIES CORELATED WITH DIAMETER AS Diameter increases V elocity of conduction increases. Magnitude of electrical response increases . Threshold of excitation decreases. Duration of response decreases . Refractory period decreases . RAJ NIDHI 18

19. A GROUP B GROUP C GROUP GROUPS OF NERVE FIBERS RAJ NIDHI 19

20. A GROUP A group is composed of largest fibers. The fibers of this group are myelinated . Both sensory and motor in function. It is found in somatic nerves as SCIATIC AND SAPHENOUS nerve . It is further classified into 4 sub groups. A α (afferent and efferent fibers) A β (afferent and efferent fibers) A γ (efferent fibers) A δ (afferent fibers) RAJ NIDHI 20

21. B GROUP The fibers of this group are myelinated . The B fibers are found solely in preganglionic autonomic nerve . RAJ NIDHI 21

22. C GROUP It is composed of smallest fibers. All the fibers of this group are unmyelinated . Mostly found in visceral and cutaneous nerve. They have high threshold i.e. 30 folds that of A group . Generally they are found in postganglionic sympathetic nerve . RAJ NIDHI 22

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24. About the nerve fibers RAJ NIDHI 24

25. Numerical classification 4 RAJ NIDHI 25

26. NUMERICAL CLASSIFICATION OF SENSORY NERVE FIBERS RAJ NIDHI 26

27. CLINICAL ASPECTS RAJ NIDHI 27

28. MULTIPLE SCLEROSIS It is autoimmune disorder. Causes may be genetic or environmental. Antibodies & white blood cells in the immune system attack myelin causing inflammation and injury of sheath . So the loss of myelin leads to leakage of k + through voltage gated channels, hyperpolarisation and failure to conduct action potential. RAJ NIDHI 28

29. Treatment for multiple sclerosis NO TREATMENT of this disease but some drug like β -INTERFERON suppresses the immune response, reduce the severity & slow the progression of disease. RAJ NIDHI 29

30. PERIPHERAL NEUROPATHY Peripheral neuropathy is damage to nerves of peripheral nervous system which may be caused by diseases or trauma. It is classified according to number of nerves affected or types of nerve cells affected (motor ,sensory, autonomic). MONONEUROPATHY It is a type of neuropathy that only affects single nerve . The most common cause of mononeuropathy is physical compression of the nerve known as compression neuropathy. MONONEURITIS MULTIPLEX It is the simultaneous or sequential involvement of the individual noncontiguous nerve trunk either partially or completely. the pattern of involvement is asymmetric. RAJ NIDHI 30

31. POLYNEUROPATHY It is pattern of nerve damage which is a quite different from mononeuropathy and often more serious and affecting more areas of body. The pattern of involvement is symmetric . AUTONOMIC NEUROPATHY It is a form of polyneuropathy which affects the involuntary system i.e. autonomic nervous system affecting mostly the internal organs. Most commonly it is seen in person with long standing diabetes mellitus type1 and 2. NEURITIS It is a general term of inflammation of a nerve or the general inflammation of the peripheral nervous system. RAJ NIDHI 31

32. REFERENCES GUYTON GANONG ’S REVIEW OF MEDICAL PHYSIOLOGY INTERNET RAJ NIDHI 32

33. T HANK YO U RAJ NIDHI 33