Nerve Fibres: Properties And Classification: Classification And Properties

What are Nerve Fibres?

Nerve fibres are vital elements of the nervous system that facilitate the transportation of electrical signals, or, in other words, nerve impulses across the body. They are essentially composed of axons which refer to the thread-like protrusions of nerve cells or, neurons. 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 functions and disease diagnosis processes meticulously.

Structure of Nerve Fibres

These are some of the critical structures of the axon are :

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

• Axolemma: Membrane that covers the axon. it is essential for the structural integrity of the nerve fiber

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

• Myelin Sheath: Myelin is a lipid material that wraps around the axon and is protective.

Classification of Nerve Fibres

Based on the different criteria there are different types of nerve fibres:

Based on Diameter & Conduction Velocity (A, B, C Fibres)

Groups A, B and C fibres can be classified according to their diameter, degree of myelination, conduction velocity and the type of function.

Based on Function

The nerve fibres are classified as either afferent or efferent based on their functional relationship to the central nervous system. Let's examine each one separately.

Based on Myelination

The nervous system contains both myelinated and unmyelinated nerve fibres. The proportional content of the two types of nerve fibres varies.

Properties of Nerve Fibres

The properties of nerve fibres have the following very basic inferences:

Conduction Velocity

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

Either all or none of the impulses are translated by a nerve fibre. An action potential will be produced if a stimulus is applied up to a threshold level. However, the action potential will not be impacted by increasing the stimulus's power.

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.

Nerve Impulse NEET MCQs (With Answers & Explanations)

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 the 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 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 the nerve impulse. The nerve impulse is the sum 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 eimple organic and inorganic molecules. The axon is immersed in the extracellular fluid (ECF). Through 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.

Also Read:

• MCQs on Introduction to Nerve Impulse

• Lobes of Cerebrum

• Cerebrospinal Fluid