Nervous tissue, dorsal root ganglion
Primary sensory neurons have axons which extend from peripheral receptors (e.g., sensory nerve endings in skin or muscle) into the spinal cord. Within the cord, these axons eventually synapse with second order sensory cells which in turn decussate and ascend to the thalamus. Cell bodies of primary sensory neurons are located in dorsal root ganglia, along the dorsal root adjacent to the cord.
The shape of primary sensory neurons is distinctive. A single long axonal process extends from each peripheral receptor into the cord, while the cell body is attached to the axon by a single short process. These cells have no dendrites.
[Some histology books perversely label the peripheral portions of sensory axons as "dendrites", simply because they carry information toward the cell bodies. But structurally and functionally, these processes are axons, conducting action potentials all the way from periphery into the cord.]
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Last updated: 8 December 2003 / dgk