Neuron: Definition, Structure, Parts, Function, Diagrams

What Is a Neuron? (Definition & Importance)

A neuron is a specific cell of the nervous system that carries electrical impulses along the pathway of the nerve, by which the brain, spinal cord, and other parts of the body can communicate with one another.

The neuron participates in the reception, processing and transmission of sensory information and motor commands to the muscles, thus they control various body functions. These are the parts of nature that have specialised cells that transfer electrical and chemical signals. Hence, they are responsible for the proper functioning of the nervous system.

Structure of a Neuron

Knowing the general structure of a neuron will help us appreciate how it works in the nervous system.

Cell Body (Soma)

The portion that includes the nucleus, regarded as the control centre of the cell.

Dendrites

These are incoming signal-receiving ends from other neurons.

Axon

Conducts electrical impulses away from the cell body

Myelin Sheath

Fatty, insulating layer of the axon, increasing the velocity of signal transmission.

Nodes of Ranvier

These are gaps in the myelin sheath that facilitate rapid transmission of signals.

Axon Terminals

These are responsible for releasing neurotransmitters to pass on the signals to the next neuron.

Types of Neurons

There can be three primary types of neurons based on their functions.

Sensory (Afferent) Neurons

These carry sensory information to the brain and spinal cord.

Motor (Efferent) Neurons

These transmit commands from the brain and spinal cord to muscles and glands.

Interneurons

These are neurons that connect other neurons, usually within the central nervous system. This means they connect sensory with motor neurons, therefore, facilitating communication between them.

Functions of Neurons

The neurons perform various crucial functions which help the nervous system function properly.

Electric Signal Transmission

The neurons transmit electrical impulses called action potential.

Synaptic Transmission

It is the process through which neurotransmitters are released to communicate with other neurons.

Neurotransmitters

Thus, neurotransmitters are the chemical mediators of the signals transmitted from one neuron to another.

The Synapse

The synapses are the junctions through which neurons communicate with each other.

• The presynaptic terminal, synaptic cleft, postsynaptic membrane.

• It allows the transmission of electrical or chemical signals from one neuron to another.

Neurogenesis and Neuron Plasticity

It is in charge of learning and recovery; it relies on the generation of new neurons and plasticity in the brain.

• Neurogenesis: The process of new neuron generation in the brain.

• Neuron Plasticity: Changes a neuron undergoes as a result of new information, sensory stimulation, development, damage, or malfunction.

Disorders Related to Neurons

Several neurological diseases are claimed to be connected to the failure of neurons.

Alzheimer’s Disease

A condition characterised by the death of neurons, and the consequences are memory loss and cognitive declines

Parkinson’s Disease

Involves the loss of dopamine-producing neurons, affecting movement and coordination.

Multiple Sclerosis

An autoimmune disorder that attacks the myelin sheath, disrupting neural communication.

Neurons NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Structure of neurons

• Types of neurons

• Disorders related to neurons

Practice Questions for NEET

Q1. The major constituents of neurofilaments are

1. Microtubules

2. Intermediate filaments

3. Actin filaments

4. Protofilaments

Correct answer: 2) Intermediate filaments

Explanation:

The main structural element in the neurons of the brain is neurofilament. They are fibrous proteins having a diameter of 10 nm.

The proteins involved as structural elements in the neurons are divided into six types based on protein structure and gene organization. Neurofilaments are classed as Type IV intermediate filaments which are found in the cytoplasm of neurons. Neurofilaments majorly consist of intermediate filaments. They provide the structural support for axons as well as regulate the diameter of the axons. These intermediate filaments are also found in cyton and dendrites and transmit nerve impulses.

Hence, the correct answer is option (2) intermediate filament.

Q2. Myelinated nerve fibres are found in

1. Spinal nerves

2. Cranial nerves

3. Autonomic nervous system

4. Both a and b

Correct answer: 4) Both a and b

Explanation:

There are two types of axons, namely, myelinated and unmyelinated. The myelinated nerve fibers are enveloped with Schwann cells, which form a myelin sheath around the axon. The gaps between two adjacent myelin sheaths are called nodes of Ranvier. Myelinated nerve fibers are found in spinal and cranial nerves. Unmyelinated nerve fiber is enclosed by a Schwann cell that does not form a myelin sheath around the axon and is commonly found in autonomous and somatic neural systems.

Hence, the correct answer is option 4) Both a and b.

Q3. Nerve fibers are surrounded by an insulating fatty layer called

1. Adipose tissue

2. Myelin sheath

3. Hyaline sheath

4. Peritoneum

Correct answer: 2) Myelin Sheath

Explanation:

The myelin sheath is an insulating fatty coating that envelops nerve fibers. By enabling electrical impulses to leap between the Nodes of Ranvier, which are openings in the myelin sheath, the sheath speeds up the transmission of nerve signals. Saltatory conduction is the mechanism that speeds up and improves neuron transmission.

Hence, the correct answer is option 2) Myelin sheath.

Also Read:

• MCQs on Structure of Neuron

• Mechanism of Vision

• Autonomic Nervous System

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