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A bipolar neuron is a sensory nerve cell that has two processes extending from the body of the cell. Classified with the nervous system, these sensory neurons detect and signal changes within the system. A bipolar neuron typically communicates with other cells in the nervous system through chemical signaling, and it is an electrically excitable cell. The presence of two processes, an axon and a dendrite, which are on opposite sides, is what makes a neuron bipolar.
Examples of bipolar neurons include retinal bipolar cells, olfactory epithelium cells, cochlear ganglia and vestibular ganglia. Each of these deals with the body's senses. Retinal cells are found in the eyes, and olfactory epithelium cells are located in the nasal cavity. The cochlear ganglia are part of the nerve that carries signals from the inner ear to the brain. The vestibular ganglia are part of the vestibular system, which regulates the body's balance.
Bipolar neurons tend to take on the oval shape when viewed in sections. Retinal cells, for instance, are a group of bipolar neurons that appear to be round when viewed through a microscope. In this area of the nervous system, the sensory neurons are classified as either "on" or "off" bipolar cells. Whereas "on" bipolar neurons are excited by glutamate's reaction to increased exposure to light, "off" bipolar cells are not exposed to large volumes of light and hence do not receive such chemical signaling.
An "on" bipolar neuron typically reacts to glutamate release by expanding in the light. The neuron is considered "off" when light exposure is minimized and the retina returns to its normal size. While "on," bipolar neurons protect the retina from cation-permeable channels.
Also classified as a bipolar neuron, the olfactory cell houses rounded nuclei and contains small vesicular structures. Olfactory cells pass between supporting cells and near the surface of the nervous system. Dendrites expand to form rods that assist in creating a layer of fluid from Bowman glands. Dendrite processes that properly operate prevent olfactory disorder.