Classification of Neuron

 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.