Nerve Fibres: Properties And Classification: Classification And Properties

What are Nerve Fibres?

Nerve fibres are vital elements of the nervous system. They facilitate the transportation of electrical signals called nerve impulses across the body. Each nerve fibre is made of an axon with a thread-like extension of neurons. These axonal fibres ensure communication between the brain, spinal cord and organs with speed and accuracy.

Knowledge of nerve fibre properties has to be gained or learned to the maximum extent by medical experts and scholars who are linked with medical studies to understand the neurological control and coordination, and disease diagnosis processes meticulously.

Properties of Nerve Fibres

Nerve fibres show special properties that control the generation, conduction, and transmission of nerve impulses in the nervous system. These properties of nerve fibres decide the speed, strength and pattern of nerve impulses. They have the following very basic inferences:

Conduction Velocity

The fibre diameter and the extent of myelination are strong determinants of conduction velocity. Group A fibres conduct faster than the slower Group B and Group C fibres.

Refractory Periods

The period during which a nerve fibre is not capable of conducting a second impulse after transmission of the first impulse. Ensures orderly conduction of nerve signals and prohibits overlap of impulses.

All-or-None Law

A nerve fibre either conducts a full impulse or none at all. An action potential will be produced if a stimulus is applied up to a threshold level. Increasing stimulus strength does not change the size of the action potential.

Summation

An action potential cannot be produced by applying a stimulus that is below the threshold. However, an action potential is produced when several sub-threshold stimuli are presented quickly one after the other.

Structure of Nerve Fibres

The structure of a nerve fibre explains how signals move inside the nervous system. Each neural fibre is made of different parts that support different properties of the nerve fibre. These are some of the critical structures of a nerve fibre given below:

• Axoplasm: The axon's cytoplasm activates the transport of metabolic activities in the nerve.

• Axolemma: It is the membrane that covers the axon. It is essential for the structural integrity of the nerve fibre.

• Nodes of Ranvier: These are the intervals of the myelin sheath along the axon. They help the impulses travel fast with saltatory conduction.

• Myelin Sheath: It is a fatty layer made of lipid material that wraps around the axon and is protective.

Types of Nerve Fibres: Myelinated and Non‑Myelinated

The human nervous system contains two major types of nerve fibres. These are myelinated and unmyelinated nerve fibres. The properties of nerve fibres depend on whether they have a myelin sheath or not. The proportional content of the two types of nerve fibres varies. The difference between a myelinated nerve fibre and a non-myelinated nerve fibre is given below:

Classification of Nerve Fibres: Group A, B, C Fibres

Nerve fibres are classified into Groups A, B and C fibres. They are classified according to their diameter, degree of myelination, conduction velocity and the type of function.

Difference between Afferent and Efferent Nerve Fibres

The nerve fibres are classified as either afferent nerve fibres or efferent nerve fibres based on their functional relationship to the central nervous system. Knowing the difference between afferent and efferent nerve fibres of neurons is important because it explains the direction of signal flow in the nervous system.

The difference between afferent and efferent nerve fibres is given below:

Nerve Impulse and Properties of Nerve Fibres MCQs for NEET

Important questions asked in NEET from this topic are:

• Classification of nerve fibres

• Properties of nerve fibres

Practice Questions for NEET

Q1. Choose the incorrect statement

1. All the nerve fibres carry information in the form of a nerve impulse

2. The interior of the axon is filled with extracellular fluid

3. Generally, the solutes in ECF and axoplasm are in ionic form

4. The electrical events in the nerve fibres are governed by the differential permeability of the axolemma to sodium and potassium ions.

Correct answer: 2) The interior of the axon is filled with extracellular fluid

Explanation:

All the nerve fibres carry information in the form of a nerve impulse. The nerve impulse is the total of physical and chemical disturbances created by a stimulus (electrical, chemical or mechanical) in a neuron or nerve fibre, which results in the movement of a wave along the nerve fibre. The nerve fibre or axon is like a cylinder. The interior of the axon is filled with axoplasm (i.e., the cytoplasm of the nerve cell). The exterior of the axon is covered with a thin membrane, the axon membrane or axolemma. Axolemma is selectively permeable for simple organic and inorganic molecules. The axon is immersed in the extracellular fluid (ECF). Through the axolemma, movement of solute takes place between the axoplasm and ECF. Generally, the solutes in ECF and axoplasm are in ionic form.

Hence, the correct answer is option 2) The interior of the axon is filled with extracellular fluid.

Q2. What is the function of the axon in a neuron?

1. To receive signals from other neurons

2. To support and protect the cell body

3. To transmit signals to other neurons

4. To synthesize neurotransmitters

Correct answer: 3) To transmit signals to other neurons

Explanation:

The function of the axon in a neuron is to transmit signals to other neurons or other cells such as muscles or glands. The axon is a long, slender projection of the neuron that carries electrical signals away from the cell body and toward the axon terminals, where neurotransmitters are released to communicate with other neurons or cells. The axon is covered by a myelin sheath, which helps to insulate and speed up the transmission of electrical signals.

Hence, the correct answer is option 3) To transmit signals to other neurons.

Q3. Resting membrane potential is maintained by

1. Hormones

2. Neurotransmitters

3. Ion pumps

4. None of the above

Correct answer: 3) Ion Pumps

Explanation:

The sodium-potassium pump and leak channels are examples of ion pumps and channels that preserve a cell's resting membrane potential:
For every ATP molecule, this pump transports two potassium ions into the cell and three sodium ions out of it. The potassium ion gradient produced by this action adds to the resting membrane potential. The electrical potential across a cell's plasma membrane when it is not activated is known as the resting membrane potential. Because more cations are released than are absorbed, the inside of the cell stays negatively charged in relation to the extracellular fluid.

Hence, the correct answer is option 3) Ion pumps.