Classification of Neuron
1.
Depending upon structure
2.
Depending upon distribution
3.
Depending upon origin
4.
Depending upon function
5.
Depending upon secretion of neurotransmitter
6.
Depending upon diameter and conduction of impulse
(ErlangerGasser classification)
DEPENDING UPON
STRUCTURE
Based on
structure, nerve fibers are classified into two types:
i. Myelinated
Nerve Fibers
Myelinated
nerve fibers are the nerve fibers that are covered by myelin
sheath.
ii. Non-myelinated
Nerve Fibers
Nonmyelinated
nerve fibers are the nerve fibers which are not covered by myelin sheath.
2. DEPENDING UPON
DISTRIBUTION
Nerve
fibers are classified into two types, on the basis of distribution:
i. Somatic Nerve
Fibers
Somatic
nerve fibers supply the skeletal muscles of the body.
ii. Visceral or
Autonomic Nerve Fibers
Autonomic
nerve fibers supply the various internal organs of the body.
3. DEPENDING UPON
ORIGIN
On the
basis of origin, nerve fibers are divided into two types:
i. Cranial Nerve
Fibers
Nerve
fibers arising from brain are called cranial nerve fibers.
ii. Spinal Nerve
Fibers
Nerve
fibers arising from spinal cord are called spinal nerve
fibers.
4. DEPENDING UPON
FUNCTION
Functionally,
nerve fibers are classified into two types
i. Sensory Nerve Fibers
Sensory
nerve fibers carry sensory impulses from different parts of the body to the
central nervous system. These nerve fibers are also known as afferent
nerve fibers.
ii. Motor Nerve
Fibers
Motor
nerve fibers carry motor impulses from central nervous system to different
parts of the body. These
nerve
fibers are also called efferent nerve fibers.
5. DEPENDING UPON
SECRETION OF NEUROTRANSMITTER
Depending
upon the neurotransmitter substance secreted, nerve fibers are divided into two
types:
i. Adrenergic
Nerve Fibers
Adrenergic nerve
fibers secrete noradrenaline.
ii. Cholinergic
Nerve Fibers
Cholinergic
nerve fibers secrete acetylcholine.
6. DEPENDING UPON
DIAMETER AND CONDUCTION OF IMPULSE
(ERLANGER-GASSER
CLASSIFICATION)
Erlanger
and Gasser classified the nerve fibers into three major types, on the basis of diameter (thickness) of the fibers and velocity of conduction
of impulses
i. Type A nerve fibers
ii. Type B nerve
fibers
iii. Type C nerve
fibers.
Among these fibers,
type A nerve fibers are the thickest fibers and type C nerve fibers are the
thinnest fibers. Type C
fibers are also known as Type IV fibers. Except type C fibers, all the nerve
fibers are myelinated.
Type A nerve fibers
are divided into four types:
a. Type A alpha or
Type I nerve fibers
b. Type A beta or Type
II nerve fibers
c. Type A gamma nerve
fibers
d. Type A delta or
Type III nerve fibers.
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