Pseudounipolar neuron

A pseudounipolar neuron (pseudo - false, uni - one) is a sensory neuron in the peripheral nervous system. This neuron contains a long dendrite and a short axon that connects to the spinal cord. The dendrite and axon are sometimes called distal process and proximal process, respectively.^[1]

The dendrite of a pseudounipolar neuron

By definition a pseudounipolar neuron has one dendrite and one axon. Just as for every neuron, the dendrite conducts nerve impulses toward the cell body, and the axon conducts them away from the cell body. However, the dendrite of a pseudounipolar neuron is structurally and functionally an axon, except at its terminal part where it contacts a specialized sensory organ.^[2] When the sensory organ transduces information, it initiates an action potential that is propagated toward the cell body. Because the dendrite functions as an axon, this potential does not degrade, but reaches the axon unabated and continues toward the central nervous system.^[3]
Because of the similarity between this dendrite and an axon, some authors describe the pseudounipolar neuron as having one process that leaves the cell body, an axon. The dendrites are placed "on top of" the axon, connected with the receptors.^[4]
In pictures, the dendrite can be both called dendrite^[5] and axon.^[6] Both pictures show that this dendrite/axon is myelinated.

Anatomy

The dendrite of these neurons is located in the nerves coming from the body. The cell bodies are located in the dorsal root ganglion just next to the spinal cord. The axons protrude through the dorsal root and into the posterior horn of the spinal cord.

Signal Pathway

The signal is conducted through the nerve (dendrite) to the dorsal root ganglion (cell body), then through the dorsal root (axon) ending at the sensory nuclei in the dorsal horn of the spinal cord.

References

External links

• Diagram at ccccd.edu
• n_07/12569975 at Dorland's Medical Dictionary
• unipolar+neuron at eMedicine Dictionary

Histology: nervous tissue
Neurons (gray matter)	soma, axon (axon hillock, axoplasm, axolemma, neurofibril/neurofilament), dendrite (Nissl body, dendritic spine, apical dendrite, basal dendrite) types (bipolar, pseudounipolar, multipolar, pyramidal, Purkinje, granule)
Afferent nerve/Sensory nerve/Sensory neuron	GSA, GVA, SSA, SVA, fibers (Ia, Ib or Golgi, II or Aβ, III or Aδ or fast pain, IV or C or slow pain)
Efferent nerve/Motor nerve/Motor neuron	GSE, GVE, SVE, Upper motor neuron, Lower motor neuron (α motorneuron, γ motorneuron)
Synapses	neuropil, synaptic vesicle, neuromuscular junction, electrical synapse - Interneuron (Renshaw)
Sensory receptors	Free nerve ending, Meissner's corpuscle, Merkel nerve ending, Muscle spindle, Pacinian corpuscle, Ruffini ending, Olfactory receptor neuron, Photoreceptor cell, Hair cell, Taste bud
Glial cells	astrocyte, oligodendrocyte, ependymal cells, microglia, radial glia
Myelination (white matter)	Schwann cell, oligodendrocyte, nodes of Ranvier, internode, Schmidt-Lanterman incisures, neurolemma
Related connective tissues	epineurium, perineurium, endoneurium, nerve fascicle, meninges