The Bipolar neurons Are a type of cells that are characterized by two extensions: an axon and a dendrite.
East Type of neurons Are less prevalent at the brain level than Multipolar neurons (Containing more than one dendrite) but more prevalent than Unipolar neurons (It contains a single extension that acts as an axon and as a dendrite at the same time).
Bipolar neurons are mainly 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, gustatory and auditory stimuli. In turn, they are also part of the vestibular functions.
These types of cells are found in the spinal ganglia when they are embryonic.
Characteristics of bipolar neurons
Bipolar neurons are those that present a cellular body elongating where at each of its ends possesses a single dendrite.
These cells are therefore characterized by two branches external to the soma or neuronal body. It differs from the unipolar because it has two extensions (the unipolar ones only contain one) and the multipolar ones because they contain only one dendrite (the multipolar ones have more than one).
The axons of the bipolar neurons are responsible for performing the functions of information transmission, while the dendrites perform the processes of capturing information from other neurons.
The nucleus of the bipolar neuron (unlike the unipolar) is located in the center. Each of its sides contains a branch. On one side the axon and on the other the dendrite.
In general, bipolar neurons are afferent. That is, they are responsible for transmitting information from the senses to the central nervous system.
The presence of this type of neurons becomes especially prominent in the spinal ganglia of the fish. Its main properties are.
Transmits nerve signals
Bipolar neurons act as receivers and as transmitters. In this sense, they are able to transmit nerve signals to other neurons and cells of the nervous system .
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.
It has an elongated shape
The morphology of this type of neurons stands out for being slightly elongated. Thus, it differs from unipolar neurons by their rounded shape and multipolar neurons by their starry morphology.
Separate stretches
The two extensions of the bipolar neurons (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 of the organism.
These cells are found in several sensory organs and transmit information to the central nervous system about the ear, the smell and the sight among others.
It is unusual
These types of neurons, despite being very important to transmit sensory information, are little prevalent in the nervous systems of humans. In fact, multipolar neurons are much more abundant than these.
Location
Bipolar neurons are distributed throughout different regions of the nervous system as well as the organism. Specifically, these types of cells are especially prevalent in the sense organs.
In this sense, the main regions of location of the 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 termini that have bipolar neurons (axon and dendrite) are connected directly with the photoreceptor cells.
The extensions of bipolar neurons are connected to the outer layer of the retina. This outer layer is mainly formed by the ganglion cells, place from where it leaves the optical nerves.
Olfactory epithelium
The olfactory epithelium is a region of the nose that is formed by olfactory receptor cells. These cells result in bipolar neurons that send their axons to the brain .
In this case, neurons have a half-life of between one and two months, so they must be replaced continuously by new cells derived from the olfactory epithelial cells.
Each of the bipolar neurons of the olfactory epithelium expresses hundreds of distinct olfactory receptor proteins, which are encoded by the corresponding genes.
The axons of these neurons are directed to a passing station known as the glomerulus. This region is located in the Olfactory bulb Of the brain, so bipolar neurons travel from the olfactory epithelium to the central nervous system.
Specifically, the projections of these cells are directed to the middle of the Temporal lobes , That is, the olfactory cortex. Also, 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 equilibrium. It is formed by several branches that come from the semicircular canals that join forming the vestibular nerve to continue advancing and to leave through the internal auditory canal.
In this way, the vestibular nerve is formed by the cochlear nerve, which carries the information about the sound and by the vestibular nerve that sends the information on the balance.
Both functions are performed by bipolar neurons, which connect these regions with the central nervous system.
Balance can be assessed by the stability of a body, which connects the ear of the brain stem. In this way, the nerve impulses are sent from the inner ear to the brain.
Finally, the inner ear contains the cochlea, a spiral-shaped duct that also contains bipolar neurons that act as transducers of sound signals.
References
- Holloway, M. (2003) Cerebral plasticity. Research and Science, November 2003.
- Interlandi, J. (2013). Break the brain barrier. Research and Science, 443, 38-43.
- Jones, A.R. I Overly, C.C. (2013). Genetic Atlas of the Brain. Mind and Brain, 58, 54-61.
- Kiernan, J.A. I Rajakumar, N. (2014). Barr. The Human Nervous System (10th Ed.). Barcelona: Wolters Kluwer Health Spain.
- Kolb, B. i Whishaw, I. (2002) Brain and Behavior. An Introduction. Madrid: McGraw-Hill / Interamericana de España, S.A.U.