BIPOLAR NEURON: PARTS, LOCATION AND FUNCTIONS - NEUROPSYCHOLOGY - 2024

A bipolar neuron is a type of cell characterized by containing two processes: an axon and a dendrite. These types of neurons are less prevalent in the brain than multipolar neurons (they contain more than one dendrite), but more prevalent than unipolar neurons (they contain a single prolongation that acts as both an axon and a dendrite).

Bipolar neurons are primarily sensory and are specialized in the transmission of nerve signals that come from specific senses. In this way, they form very important cells in the reception of olfactory, taste and auditory stimuli. In turn, they are also part of the vestibular functions.

Bipolar neuron

Parts of a bipolar neuron

Bipolar neurons are those that have an elongated cell body where each end has a single dendrite. These types of cells are found in the spinal ganglia when they are embryonic.

These cells are therefore characterized by presenting two branches external to the soma or neuronal body. It differs from unipolar because it has two extensions (unipolar only contains one) and multipolar because it contains only one dendrite (multipolar has more than one).

The axons of the bipolar neurons are responsible for carrying out the information transmission functions, while the dendrites carry out the processes of capturing information from other neurons.

The nucleus of the bipolar neuron (unlike the unipolar ones) is located in the center. On each of its sides it contains a branch. On one side the axon and on the other the dendrite.

In general, bipolar neurons are afferents. That is, they are responsible for transmitting information from the senses to the central nervous system.

Functions and Features

Source: Kaya Moyan / Public domain

The functions and characteristics of bipolar neurons are:

They transmit nerve signals

Bipolar neurons act as receptors and as transmitters. In this sense, they are capable of transmitting nerve signals to other neurons and cells of the nervous system.

They send information from the periphery

The main function of this type of neurons is to capture information from the sensory organs and transmit it to brain regions.

For this reason, bipolar neurons stand out for sending information from the periphery to the central nervous system.

They have an elongated shape

The morphology of this type of neuron stands out for being slightly elongated. Thus, it differs from unipolar neurons by its rounded shape and from multipolar neurons by its stellate morphology.

Separate extensions

The two processes that bipolar neurons present (axon and dendrites) are separated from each other. The axon is located on one side of the neuronal soma while the dendrites are located on the other side.

Involved in sensory processes

Bipolar neurons are essential cells for the transmission of sensory information from the body.

These cells are found in various sensory organs and transmit information to the central nervous system about hearing, smell and sight, among others.

Unusual

These types of neurons, despite being very important for transmitting sensory information, are not very prevalent in the nervous systems of human beings. In fact, multipolar neurons are much more abundant than these.

Location

Bipolar neurons are distributed in different regions of both the nervous system and the body. Specifically, these types of cells are especially prevalent in the sensory organs.

In this sense, the main regions of location of bipolar neurons are:

Retina of the eye

The cells of the retina of the eye are located in the intermediate region of the same. The two endings that bipolar neurons have (axon and dendrite) connect directly with photoreceptor cells.

The processes of bipolar neurons are connected to the outer layer of the retina. This outer layer is made up mainly of ganglion cells, the place from which the optic nerves start.

Olfactory epithelium

The olfactory epithelium is a region of the nose that is made up of olfactory receptor cells. These cells are bipolar neurons that send their axons to the brain.

In this case, the neurons have a half-life of between one and two months, so they must be continuously replaced by new cells derived from the stem cells of the olfactory epithelium.

Each of the bipolar neurons of the olfactory epithelium expresses hundreds of different olfactory receptor proteins, which are encoded by the corresponding genes.

The axons of these neurons make their way to a way station known as the glomerulus. This region is located in the olfactory bulb of the brain, whereby bipolar neurons travel from the olfactory epithelium to the central nervous system.

Specifically, the projections of these cells are directed to the intermediate part of the temporal lobes, that is, the olfactory cortex. Likewise, some are transported to the hippocampus and the tonsillar nucleus.

Vestibulo-cochlear nerve

The vestibular nerve is a nerve that is located in the inner ear. This structure is responsible for the function of balance. It is made up of several branches that come from the semicircular canals that join together to form the vestibular nerve to continue advancing and exit through the internal auditory canal.

In this way, the vestibular nerve is formed by the cochlear nerve, which carries information about sound and by the vestibular nerve, which sends information about balance.

Both functions are performed by bipolar neurons, which connect these regions to the central nervous system.

Balance can be assessed by the stability of a body, which connects the ear to the brain stem. In this way, nerve impulses are sent from the inner ear to the brain.

Finally, the inner ear contains the cochlea, a spiral-shaped conduit that also contains bipolar neurons that act as transducers for sound signals.

References

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