Unipolar neuron

A nerve cell ( neuron) is called unipolar ( also monopolar ) if it has only one process (axon ) and no processes ( dendrites ).

Description

Under the microscope, these nerve cells look like a golf ball on a big T. Their cell body is round to slightly oval and contains the center of the nucleus. The cell body rises only a single nerve fiber. This extension can be divided in pseudounipolar T-shaped cells into two branches, the one leading to the body periphery and sensory information registered (receptive ), while the other transmits them to the central nervous system or spinal cord. However, synaptic contacts between neurons of a sensory ganglion consist neither. Most of unipolar neurons receive sensory events such as touch and temperature changes of skin, joints and muscles. This rezeptorische extension is located in the apical region of the cell body. It will be sent a basal axon. Certain areas of the extension serve as receptive surfaces, others for transmitter release. Typical unipolar cells are the rod cells of the retina to the photoreceptors.

Occurrence

Unipolar cells are more specific to the nervous system of invertebrates. However, they also come in vertebrates, including humans before. Both in vertebrates and in invertebrates, many primary sensory neurons are unipolar. These typically have a special structure to translate a physical stimulus (light, sound, temperature, etc. ) into an electrical signal and to pass this on to the brain or spinal cord. However, the independent occurrence in the differentiated nervous tissue is controversial and there is also the view represented, they came in vertebrates only in the embryo during histogenesis of nerve cells.

Invertebrates

Unipolar neurons are often found in insects, where the cell body is locates on the periphery of the brain, and is electrically inactive.

Vertebrate / human

Especially in sensory ganglia. They are found especially as oval swelling on the dorsal roots of spinal nerves as well as on the roots of certain cranial nerves. Frequently, the first neuron of the neurons of the retina, called ( rods and cones ), which is located in the retina at the bottom as unipolar nerve cells. Unipolar neurons are also found in the olfactory mucosa.

Formation

Looking at their embryonic development, all types of nerve cells have the same origin. From the epithelium of the neural tube is common stem cell for neurons and glial cells, which Neurogliablasten (short neuroblasts ) that develop after cleavage of their gliären cell lines to stem cells of the nerve cells differentiate. Because these cells produce only one extension, they are referred to as unipolar neuroblasts. This divide mitotically and will end their differentiation into mature neurocyte. In the final stage of this development, the nerve cells can no longer divide and get after the last mitosis their final form and the training of their appendages.

These are then morphologically by number of projections divided into: unipolar, bipolar, and multipolar neurons pseudounipolar.

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