Parts of a neuron and their functions

The neuron and nervous system

Introduction to neurons and glia. How the structure of a neuron allows it to receive and transmit information.

The neuron and nervous system

Biology is brought to you with support from the Amgen Foundation

Neurons (also called neurones or nerve cells) are the fundamental units of the brain and nervous system, the cells responsible for receiving sensory input from the external world, for sending motor commands to our muscles, and for transforming and relaying the electrical signals at every step in between. More than that, their interactions define who we are as people. Having said that, our roughly 100 billion neurons do interact closely with other cell types, broadly classified as glia (these may actually outnumber neurons, although it’s not really known).

The creation of new neurons in the brain is called neurogenesis, and this can happen even in adults.

What does a neuron look like?

A useful analogy is to think of a neuron as a tree. A neuron has three main parts: dendrites, an axon, and a cell body or soma (see image below), which can be represented as the branches, roots and trunk of a tree, respectively. A dendrite (tree branch) is where a neuron receives input from other cells. Dendrites branch as they move towards their tips, just like tree branches do, and they even have leaf-like structures on them called spines.

The axon (tree roots) is the output structure of the neuron; when a neuron wants to talk to another neuron, it sends an electrical message called an action potential throughout the entire axon. The soma (tree trunk) is where the nucleus lies, where the neuron’s DNA is housed, and where proteins are made to be transported throughout the axon and dendrites. 

There are different types of neurons, both in the brain and the spinal cord. They are generally divided according to where they orginate, where they project to and which neurotransmitters they use.

Concepts and definitions

Axon – The long, thin structure in which action potentials are generated; the transmitting part of the neuron. After initiation, action potentials travel down axons to cause release of neurotransmitter.

Dendrite – The receiving part of the neuron. Dendrites receive synaptic inputs from axons, with the sum total of dendritic inputs determining whether the neuron will fire an action potential.

Spine – The small protrusions found on dendrites that are, for many synapses, the postsynaptic contact site.

Action potential – Brief electrical event typically generated in the axon that signals the neuron as 'active'. An action potential travels the length of the axon and causes release of neurotransmitter into the synapse. The action potential and consequent transmitter release allow the neuron to communicate with other neurons.

Author: Dr Alan Woodruff

1. Biological Psychology
2. Neuroscience
3. Neurons

An Easy Guide to Neuron Anatomy with Diagrams

By Olivia Guy-Evans, updated August 09, 2022

by Saul Mcleod, PhD

Function   |   Anatomy   |   Types

Neurons are the information processing units of the brain which have a responsibility for sending, receiving, and transmitting electrochemical signals throughout the body.

Neurons, also known as nerve cells, are essentially the cells that make up the brain and the nervous system. Neurons do not touch each other, but where one neuron comes close to another neuron, a synapse is formed between the two.

According to new research, the human brain contains around 86 billons neurons (Herculano-Houzel, 2009). These cells develop around fully around the time of birth but unlike other cells, cannot reproduce or regenerate once they die.

Behance Discovery - Alexey Kashpersky

How do Neurons Work?

Neurons lie adjacent to each other but are not connected. There is a very small gap between neurons called a synapse.

The function of a neuron is to transmit nerve impulses along the length of an individual neuron and across the synapse into the next neuron. The electrical signals transmitted by neurons are called action potentials.

The electrical signal needs to cross the synaptic gap to continue on its journey to, or from, the CNS. This is done using chemicals which diffuse across the gap between the two neurons. These chemicals are called neurotransmitters.

During synaptic transmission, the action potential (an electrical impulse) triggers the synaptic vesicles of the pre-synaptic neuron to release neurotransmitters (a chemical message).

These neurotransmitters diffuse across the synaptic gap (the gap between the pre and post-synaptic neurons) and bind to specialised receptor sites on the post-synaptic neuron. This will then trigger an electrical impulse in the adjacent cell.

The central nervous system, which comprises the brain and spinal cord, and the peripheral nervous system, which consists of sensory and motor nerve cells all contain these information processing neurons.

The neuron contains the soma (cell body) from which extend the axon (a nerve fiber conducting electrical impulses away from the soma) and dendrites (tree-like structures that receive signals from other neurons). The myelin sheath is an insulating layer that forms around the axon and allows nerve impulses to transmit more rapidly along the axon.

Neurons do not touch each other, and there is a gap, called the synapse, between the axon of one neuron the dendrite of the next.

The unique structure of neurons permits it to receive and carry messages to other neurons and throughout the body.

Dendrites

Dendrites are the tree-root-shaped part of the neuron which are usually shorter and more numerous than axons. Their purpose is to receive information from other neurons and to transmit electrical signals towards the cell body.

Dendrites are covered in synapses, which allows them to receive signals from other neurons. Some neurons have short dendrites, whilst others have longer ones.

In the central nervous system, neurons are long and have complex branches that can allow them to receive signals from many other neurons.

For instance, cells called Purkinje cells which are found in the cerebellum have highly developed dendrites to receive signals from thousands of other cells.

Soma (Cell Body)

The soma, or cell body, is essentially the core of the neuron. The soma’s function is to maintain the cell and to keep the neuron functioning efficiently (Luengo-Sanchez et al., 2015).

The soma is enclosed by a membrane which protects it, but also allows it to interact with its immediate surroundings.

The soma contains a cell nucleus which produces genetic information and directs the synthesis of proteins. These proteins are vital for other parts of the neuron to function.

Axon

The axon, also called a nerve fiber, is a tail-like structure of the neuron which joins the cell body at a junction called the axon hillock.

The function of the axon is to carry signals away from the cell body to the terminal buttons, in order to transmit electrical signals to other neurons.

Most neurons just have one axon which can range in size from 0.1 millimeters to over 3 feet (Miller & Zachary, 2017). Some axons are covered in a fatty substance called myelin which insulates the axon and aids in transmitting signals quicker.

Axons are long nerve processes that may branch off to transfer signals to many areas, before ending at junctions called synapses.

Myelin Sheath

The myelin sheath is a layer of fatty material that covers the axons of neurons. Its purpose is to insulate one nerve cell from another and so to prevent the impulse from one neuron from interfering with the impulse from another. The second function of the myelin sheath is to speed up the conduction of nerve impulses along the axon.

The axons which are wrapped in cells known as glial cells (also known as oligodendrocytes and Schwann cells) form the myelin sheath.

The myelin sheath which surrounds these neurons has a purpose to insulate and protect the axon. Due to this protection, the speed of transmission to other neurons is a lot faster than the neurons that are unmyelinated.

The myelin sheath is made up of broken up gaps called nodes of Ranvier. Electrical signals are able to jump between the nodes of Ranvier which helps in speeding up the transmission of signals.

Axon Terminals

Located at the end of the neuron, the axon terminals (terminal buttons) are responsible for transmitting signals to other neurons.

At the end of the terminal button is a gap, which is known as a synapse. Terminal buttons hold vessels which contain neurotransmitters.

Neurotransmitters are released from the terminal buttons into the synapse and are used to carry signals across the synapse to other neurons. The electrical signals convert to chemical signals during this process.

It is then the responsibility of the terminal buttons to reuptake the excess neurotransmitters which did not get passed onto the next neuron.

Types of Neurons

Although there are billions of neurons and vast variations, neurons can be classified into three basic groups depending on their function: sensory neurons (long dendrites and short axons), motor neurons (short dendrites and long axons) and relay neurons (short dendrites and short or long axons).

Sensory Neurons

Sensory neurons (sometimes referred to as afferent neurons) are nerve cells which carry nerve impulses from sensory receptors towards the central nervous system and brain. When these nerve impulses reach the brain, they are translated into ‘sensations’, such as vision, hearing, taste and touch.

This sensory information can be either physical – through sound, heat, touch, and light, or it can be chemical – through taste or smell. An example of this can be when touching an extremely hot surface. Once this happens, the sensory neurons will be sending signals to the central nervous system about the information they have received.

Most sensory neurons are characterized as being pseudounipolar. This means that they have one axon which is split into two branches.

Motor Neurons

Motor neurons (also referred to as efferent neurons) are the nerve cells responsible for carrying signals away from the central nervous system towards muscles to cause movement. They release neurotransmitters to trigger responses leading to muscle movement.

Motor neurons are located in the brainstem or spinal cord (parts of the central nervous system) and connect to muscles, glands and organs throughout the body.

These types of neurons transmit signals from the spinal cord and brainstem to skeletal and smooth muscle to either directly or indirectly control muscle movements.

For instance, after touching a hot surface with your hand, the message has been received from the sensory neurons. The motor neurons then cause the hand to move away from the hot surface.

There are two types of motor neurons:

• Lower motor neurons – these are neurons which travel from the spinal cord to the muscles of the body.
• Upper motor neurons – these are neurons which travel between the brain and the spinal cord.

Motor neurons are characterized as being multipolar. This means that they have one axon and several dendrites projecting from the cell body.

Relay Neurons

A relay neuron (also known as an interneuron) allows sensory and motor neurons to communicate with each other. Relay neurons connect various neurons within the brain and spinal cord, and are easy to recognize, due to their short axons.

Alike to motor neurons, interneurons are multipolar. This means they have one axon and several dendrites.

As well as acting as a connection between neurons, interneurons can also communicate with each other through forming circuits of differing complexities.

The communication between interneurons assists the brain to complete complex functions such as learning and decision-making, as well as playing a vital role in reflexes and neurogenesis – which means the regeneration of new neurons.

About the Author

Olivia Guy-Evans obtained her undergraduate degree in Educational Psychology at Edge Hill University in 2015. She then received her master’s degree in Psychology of Education from the University of Bristol in 2019. Olivia has been working as a support worker for adults with learning disabilities in Bristol for the last four years.

How to reference this article:

Guy-Evans, O. (2021, Feb 15). What is a neuron? Function, parts, structure, and types. Simply Psychology. www.simplypsychology.org/neuron.html

APA Style References

Herculano-Houzel, S. (2009). The human brain in numbers: a linearly scaled-up primate brain. Frontiers in human neuroscience, 3, 31.

Luengo-Sanchez, S., Bielza, C., Benavides-Piccione, R., Fernaud-Espinosa, I., DeFelipe, J., & Larrañaga, P. (2015). A univocal definition of the neuronal soma morphology using Gaussian mixture models. Frontiers in neuroanatomy, 9, 137.

Miller, M. A., & Zachary, J. F. (2017). Mechanisms and morphology of cellular injury, adaptation, and death. Pathologic basis of veterinary disease, 2.

Further Information

Snapse (Kahn Academy) What is a Synapse Nicholls, J. G., Martin, A. R., Wallace, B. G., & Fuchs, P. A. (2001). From neuron to brain (Vol. 271). Sunderland, MA: Sinauer Associates. Pereda, A. E. (2014). Electrical synapses and their functional interactions with chemical synapses. Nature Reviews Neuroscience, 15(4), 250-263.

Home | About Us | Privacy Policy | Advertise | Contact Us

Simply Psychology's content is for informational and educational purposes only. Our website is not intended to be a substitute for professional medical advice, diagnosis, or treatment.

© Simply Scholar Ltd - All rights reserved

What are the 3 main parts neurons?

What are the 5 components of a neuron?

What are the 3 types of neurons and their functions?

What are the neurons parts?