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. PRESENTER
ROLL NO 119
PARA G2

2. NEURON
• It is the structural and the functional unit of
nervous system.
• The human nervous system contains
approximate 1012 neurons.

3. STRUCTURE OF NEURON

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.

6. Depending upon STRUCTURE

8. MYELINSHEATH In peripheral nervous system it is formed by
schwann’s cell. While in case of central nervous
system it is formed by oligodendroglia.
COMPOSITION
PROTEINS
LIPIDS(CHOLESTEROL,
LECITHIN &
SPHINGOMYELIN)

9. MYELINSHEATH 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

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

11. Depending upon DISTRIBUTION

13. SOMATICNERVEFIBERS
 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.

14. AUTONOMICNERVEFIBERS
 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.

15. SYMPATHETICAND
PARASYMPATHETICNERVEFIBERS 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

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

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
• Velocity of conduction increases.
• Magnitude of electrical response increases.
• Threshold of excitation decreases.
• Duration of response decreases.
• Refractory period decreases.

19. • A GROUP
• B GROUP
• C GROUP
GROUPS OF NERVE FIBERS

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.
• Aα (afferent and efferent fibers)
• Aβ (afferent and efferent fibers)
• Aγ (efferent fibers)
• Aδ (afferent fibers)

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

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.

24. About the nerve fibers
RAJ NIDHI 24

25. Numerical classification

26. NUMERICAL CLASSIFICATION OF SENSORY NERVE FIBERS

27. 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. 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. RAJ NIDHI 33