classification of nerve fibers:-
-based on number of process:-
1)unipolar
2)bipolar
-based on the presence of myelin sheath.
1)myelinated 2) non myelinated.
-based on function.
1)sensory-transmitting message from peripheral to CNS.
2)motor-transmit message from CNS to muscle.
3)mixed-interneurons connect sensory and motor.
-based on type of neurotransmitter.
1)cholinergic-acetylcholine,
2)Adrenergic-adrenaline.
3)dopaminergic.-dopamine.
-based on thickness.and diameter.
ERLANGER GANSER'S CLASSIFICATION.
*saltatory conduction:
In myelinated nerve fiber ,myelin sheath is intercepted by nodes of ranvier ,depolarisation jumps from first node to another.
-their type of conduction saltatory conduction.
Faster conduction.
-energy required is less because electrolyte is present only at nodemore number of Na+ k+ ions are present.
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-factors affecting conduction of nerve impulse.
1)thickness of nerve fiber
2)myelination
3)Temperature
4)pressure reduces the conduction.
5)local anesthetic reduces the conduction.
6)hypoxia reduces the conduction.
-Nerve injury to nerve fiber.
Neurons -no multiplication no centrosome.
CNS-no regeneration.
PNS-regeneration occurs.
*Degeneration.
Wallerian degeneration.
-degeneration at distal end
1)axoplasm breaks into bits.
2)disappearance of myelin sheath.
3)debris cleared by macrophages.
4)hollow tube (ghost tube)
-degeneration at proximal end.
1)soma swells up
2)nucleus eccentric.
3)nissl granules.-chromatolysis.
regeneration
1)sprout arise from proximal end to distal one of sprouts enter in to c tubule
2)schwann cells multiply
3)axoplasm formed.
4)soma regains shape.
5)neurons come to the center
6)appearance of nissl granules.
*Synapse
Definition:-junction between two neurons.
There are about 10^14 synapse in CNS
Classification:-
-according to structure
2)axodendritic
3)axosomatic
4)dentrodentrite.
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-according to function:-
1)chemical
2)electrical.
-Structure
Steps involved in transmission of impulse
1)arrival of action potential at presynaptic membrane.
2)influx of calcium from ECF to pre synaptic membrane.
3)in response-exocytosis -release of vesicles.
4)The neuroreceptor attaches to the receptor on the postsynaptic membrane.
5)permeability of Na+-increases more in postsynaptic membrane
6)Development of action potential-depolarisation of postsynaptic membranes.
7)if neurotransmitter is excitatory -Ach called as excitatory postsynaptic membrane.
8)if neurotransmitter is inhibitory -GABA
Properties of synapse
1)synaptic delay:-time taken to release of neurotransmitter from presynaptic (duration-0.5sec)
2)one way conduction transmission of neurotransmitter from pre to postsynaptic membrane.
3)fatigue:-repeated stimuli given temporarily.-no response.
Synapse in the rate of fatigue -exhaustion of neurotransmitters .
4)summation- two or more stimuli applied responses will be summated.
a)temporal summation-stimulus applied successively ie,one after other (related to time)
b)spatial summation-stimulus applied simultaneously at different points to the same neurons.
5)convergence and divergence.
6)occlusion:-
t1+t2=T
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