Motor Neuron: Diagram, Characteristics and Diseases (original) (raw)

Last Updated : 23 Jul, 2025

**Motor neurons are nerve cells that send signals from the brain to the peripheral nervous system to initiate an action. Motor neurons have two main subtypes, upper motor neurons and lower motor neurons. Upper motor neurons originate in the brain and travel downward to connect with the lower motor neurons.

The structure of a motor neuron consists of a cell body, dendrites, and an axon. Motor neurons allow us to speak, swallow, move, and breathe. In this article, we will study the motor neuron and understand the structure and function of motor neurons with a well-labeled diagram.

Table of Content

What are Motor Neurons?

Motor neurons are also known as efferent neurons, which means they carry information from the central nervous system (CNS) to muscles and other peripheral systems. Motor neurons are named so for their role, which is to stimulate muscle contraction and movement. The cell body of the motor neuron is located in the motor cortex, brainstem, or spinal cord, and the axon (fiber) projects to the spinal cord to directly or indirectly control effector organs, mainly muscles and glands.

Motor neurons have the longest nerve fibers in the body, with a single axon stretching from the base of the spinal cord to the toes. The connection between a motor neuron and the muscle it controls is known as the neuromuscular junction. At this junction, the motor neuron releases neurotransmitters (such as acetylcholine), which bind to receptors on the muscle fibers, leading to muscle contraction.

**Also Read: Cranial Nerves: Function, Anatomy and Location

Diagram of Motor Neuron

A diagram of the motor neuron is as follows:

Diagram-Motor-Neuron

Structure of Motor Neuron

Motor neurons are multipolar, meaning they have a single axon and multiple dendrites. The structure of the motor neuron is as follows:

Also Read: Difference Between Axon and Dendrite

Characteristics of Motor Neuron

Motor neuron are a type of nerve fibres that controls the muscle movement. Some of the characteristics of the motor neurons are as follows:

Functions of Motor Neuron

Function of the motor neuron includes:

Motor Neuron Diseases

Motor neuron diseases (MNDs) are a group of rare neurological disorders that destroy motor neurons, the cells that control skeletal muscle activity. Motor neuron diseases are progressive, damage parts of the nervous system and cause muscle weakness, atrophy, and eventual loss of motor function. Some of the common motor neuron diseases are:

**Amyotrophic Lateral Sclerosis (ALS)

The most common form of motor neuron diseases and accounts for about 60–70% of cases. In ALS, both upper and lower motor neurons degenerate at the same time. Men are more commonly affected than women. It leads to muscle weakness, paralysis, and difficulties in speaking, swallowing, and breathing.

Primary Lateral Sclerosis (PLS)

It is similar to ALS, but only affects upper motor neurons. It leads to muscle stiffness, weakness, and difficulty with balance and coordination. It progresses more slowly than ALS.

**Spinal Muscular Atrophy (SMA)

SMA is a type of genetic disorder caused by the degeneration of lower motor neurons in the spinal cord. and effect the central nervous system and voluntary muscle movement. It gradually leads to muscle weakness and atrophy.

**Progressive Bulbar Palsy (PBP)

Progressive bulbar palsy (PBP) is a motor neuron disease that affects the brain stem and the nerves that supply the bulbar muscles. It affects both upper and lower motor neurons. It can lead to difficulties in speaking, swallowing, and respiratory problems.

**Hereditary Spastic Paraplegia (HSP)

Hereditary spastic paraplegia (HSP) is a group of rare inherited disorders that cause weakness and stiffness in the leg muscles. It's also known as familial spastic paraparesis. It affect the upper motor neurons.

**Kennedy's Disease (Spinal and Bulbar Muscular Atrophy)

Kennedy's disease, also known as spinal and bulbar muscular atrophy (SBMA), is a rare, inherited neuromuscular disorder that affects lower motor neurons. It causes progressive muscle weakness and wasting, particularly in the arms and legs.

Also Read: Difference Between Neurons And Neuroglia

Motor Neurone Disease Causes

The exact causes of Motor Neuron Disease (MND), are not fully understood. The disease often occurs sporadically without a clear identifiable cause. Some factor that causes disease are:

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