Peripheral nerve : functional component

 Classification of peripheral nerve according to function:

·         afferent (sensory nerve)

·         efferent (motor nerve)

·         both afferent and efferent (mixed nerve)

 

What do you mean by the Functional component of peripheral nerve?

Peripheral nerves are functionally, split into two groups: afferent (sensory nerve) and efferent (motor nerve), with seven additional subgroups referred to as functional components of the peripheral nerve.

 

Some important information about functional components of nerve

·         Sensory nerves have four functional components, compared to three for motor nerves.

·         Each sensory or motor nerve may carry one or more functional components.

·         Mixed nerves carry two or more functional components—at least one from the sensory functional component and at least one from the motor functional component.

 

Functional component in sensory nerve

·         Depending on the type of sensation and the structures involved, the sensory nerve has four distinct functioning parts.

·         General refers to universal feelings like touch, heat, pain, etc.

·         General somatic refers to sensations that are gathered from the skin or other bodily surfaces.

·         General visceral refers to sensations that originate from the body's interior organs.

·         Special somatic refers to the collection of unique sensations from the eye (vision), ear (hearing), and balance and organs of sensation situated in the outer part of the body.

·         Special visceral refers to unique feelings such as the tongue (oral cavity) for taste and the nasal cavity for smell and sensory organ are situated inner part of body.

 

Functional component in motor nerve

 

·         Efferent means motor nerve fibers that innervate skeletal muscle, cardiac muscle, smooth muscle, or glands.

·         General somatic means this nerve fiber innervates skeletal muscle, which developed from mesoderm (somite).

·         General visceral means this nerve fiber innervates a cardiac muscle, smooth muscle, or gland.

·         Special visceral means these nerve fibers innervate skeletal muscle, which developed from branchial arches.

 

 

Part 3 B

1.       Classification of nerve fibers according to the size of diameter and velocity of impulse conduction,

2.       Classification of nerve fibers according to the type of neurotransmitter released from their terminals

3.       Classification of nerve fiber according to Histologically or based on the presence or absence of myelin sheath

4.      Myelination

Classification of nerve fibers according to the size of diameter and velocity of impulse conduction,

 

 

A and B fibers are myelinated, whereas C fiber is not. 

 

Classification of nerve fibers according to the type of neurotransmitter released from their terminals

1.        adrenergic,

2.       cholinergic,

3.       dopaminergic, etc.

 

Classification of nerve fiber, according to histologicallyor based on the presence or absence of myelin sheath

1.        myelinated nerve fiber

2.       non-myelinated nerve fiber

 

What do you mean by Myelin sheath of axon or nerve fiber ?

Axon of neuron is covered by sheaths which are modified cell membranes of Schwann cells in PNS and oligodendrocytes  in CNS.

Function of myelination

•          It acts as an electrical  insulator

•          Helps in impulse conduction

The Myelin sheath of PNS derived from Schwann cells

one Schwann cell provides myelination for one axon. One Schwann cell wraps only a short segment of one axon, so to wrap an axon many Schwann cells are needed. Regeneration of PNS is possible due to the presence of neurolemmal sheath

The Myelin sheath of CNS is derived from oligodendrocytes. One oligodendrocyte has several processes that wrap up 3 to 50 of the axons of separate neurons. Each process of oligodendrocyte covers a short segment of axon like Schwann cell)