Unipolar, multipolar, and bipolar neurons are all types of nerve cells that are responsible for transferring information throughout animal bodies. Neurons use electrical impulses and chemical signals to transmit information between the central nervous system (CNS) and the rest of the body.
There are different types of neurons, and scientists distinguish each type by its number of components and its structure.
Multipolar neurons can transfer the most information between cells, and they are the most common form of neuron in the human nervous system.
This article takes a closer look at unipolar, bipolar, and multipolar neurons.
A neuron is a nerve cell that passes information around the body
The components of the neuron work together to facilitate nerve function. The
- Cell body, or soma: The cell body has a nucleus that contains the cell’s genetic material and controls the cell’s activities.
- Axon: This part, which looks like a long tail, transmits signals from the cell.
- Dendrite: This part, which looks like the branches of a tree, receives signals for the cell.
Neurons send information to each other by transmitting chemical signals called neurotransmitters across special junctions called synapses. These synapses are present at the tips of dendrites.
There are several types of neurons with different structures. Some neurons contain multiple dendrites, while others have none. The types include:
- unipolar neurons
- pseudounipolar neurons
- bipolar neurons
- multipolar neurons
- anaxonic neurons
A unipolar neuron only has one nerve process extending from the cell body: an axon that extends into dendrites.
Although the human body does not contain unipolar neurons, pseudounipolar neurons are present. A pseudounipolar neuron is a cell that only occurs as a sensory neuron.
In a pseudounipolar neuron, the nerve process extending from the cell body splits into two branches or axons. As a result, the neuron has two separate axons that independently divide into dendrites at the ends. This form is similar to that of a bipolar neuron.
A bipolar neuron has two distinct structures extending from the cell body. One is an axon, and the other is a dendrite.
Bipolar neurons are uncommon and only occur in a few specific areas within the body. These include:
- the olfactory epithelium, which is nerve tissue that runs along the nasal cavity and plays a role in smell
- the retina, a thin layer of tissue at the back of the eye that receives light signals
- certain nerves within the ear
Multipolar neurons are the most common type of neurons in the human body. They are present throughout a person’s CNS, including the brain and associated nerves in the autonomic nervous system.
A multipolar neuron has the highest number of structures extending from the cell body. There is only one axon, but each cell has many dendrites, making it easier for the neuron to exchange information.
Unipolar, bipolar, and multipolar neurons have some similar characteristics. They all
Despite occurring in different areas within the body, the neurons play a similar role, as they are responsible for passing information between the brain and the CNS.
The number and structure of components
The structure of bipolar neurons is similar to that of pseudounipolar neurons in that two distinct structures stem from the cell body. However, instead of starting as one extension that splits into two, the structures grow independently out of the cell body. The structure of a multipolar neuron is different again, as more than two structures extend from the cell body.
The table below summarizes the differences between unipolar, bipolar, and multipolar neurons.
|Occurrence in the human body||none||rare||common|
|Location||—||ear, nose, eye||throughout the CNS|
|Structure||one extension from the cell body, containing one axon with dendrites at its tip||two extensions from the cell body, including one axon and one dendrite||multiple extensions from the cell body, including one axon and many dendrites|
Below, we answer some common questions about unipolar, bipolar, and multipolar neurons.
Is a sensory neuron unipolar, bipolar, or multipolar?
Most of the sensory neurons in a human body are pseudounipolar. However, unipolar and bipolar types can also be sensory neurons.
What anatomical characteristics determine whether a neuron is unipolar, bipolar, or multipolar?
The structural components of a neuron determine whether it is unipolar, bipolar, or multipolar. These components are called axons, which transmit information, and dendrites, which receive information.
- A unipolar neuron has one axon which extends into dendrites, though this splits into two parts in pseudounipolar neurons.
- A bipolar neuron has two completely independent structures extending from the cell body, one of which is an axon and the other a dendrite.
- A multipolar neuron only has one axon extending from the cell body, but multiple dendrites grow out of it, making transmitting information easier.
Are unipolar neurons present in humans?
No, humans do not have unipolar neurons. However, they do have pseudounipolar neurons.
Neurons are nerve cells that transfer information around the body, and some types form part of the CNS. The three main types of neurons are unipolar, bipolar, and multipolar. Other forms, including pseudounipolar and anaxonic neurons, also exist.
Three major components make up a neuron. These are the cell body, axons, and dendrites. The arrangement of these components determines the type of neuron.
Unipolar neurons are the simplest form, with one axon extending from the cell body. The axon splits up into dendrites at the ends. Unipolar neurons do not occur in humans.
Bipolar neurons have one axon and one dendrite extending from the cell body. Their presence in humans is limited, but they play an important role within the ears, nose, and eyes.
Multipolar neurons are the most complex and commonly occurring type of neuron within the human body. Each neuron has one axon but multiple dendrites extending from the cell body. Multipolar neurons occur throughout the CNS.