Neuron Classification by Structure
– Unipolar –
Unipolar neurons have only one “neuronal process” (extension, branch, appendage) extending out of their cell body. Many primary sensory neurons, which are the first step in translating chemicals, light, or vibrations from the outside world into neural signals, are unipolar cells. In addition, unipolar brush cells have been found in the cerebellar cortex and cochlear nucleus (part of the brainstem).
– Bipolar –
Bipolar neurons have two long processes that extend from the soma (cell body). One process carries info away from the soma (called “axon”), and the other carries info towards the soma (called “dendrite”). Many non-primary sensory neurons,which filter or amplify signals from primary sensory neurons, are bipolar neurons. Bipolar neurons are found in the retina, olfactory epithelium, vestibular nerve, and spinal ganglia.
– Pseudounipolar –
Pseudounipolar neurons are a type of sensory neuron in the peripheral nervous system, whose somas are located within the dorsal root ganglia of the spinal cord. These neurons have a single, long axon that splits into two branches: a “peripheral branch” which goes to the skin, joints, and muscles; and a “central branch” which goes to the spinal cord. Pseudounipolar neurons develop from bipolar neurons.
– Multipolar –
The soma of multipolar neurons is surrounded by many small, branching dendrites, and one long axon. Multipolar neurons function as motor neurons and interneurons, and they are found mostly in the cortex of the brain, spinal cord, and autonomic ganglia.
– Anaxonic –
Anaxonic neurons have many processes extending out from their somas, but no axon can be differentiated from the dendrites purely based on structure. These neurons act as “non-spiking” neurons, which use graded potentials (as opposed to “spiking neurons”, which use action potentials) to effect the fidelity, strength, and lifetime of a neuronal signal. Anaxonic neurons can influence the electrical excitability of spiking neurons, and almost all central nervous system neurons born in adulthood seem to be anaxonic; however, these neurons are still very poorly understood. Anaxonic neurons have been found in the brain and special sense organs of vertebrates, and in the central nervous system of invertebrates.
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Vigilante Intergalactic Roustabout Scholars (VIRS) by Danbee Kim is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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