Peripheral Nervous System
Peripheral Nervous System

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spinal nerve ► (PNS) spinal nerve histology ► - anatomy of spinal nerves - all spinal nerves are mixed nerves, with both somatic motor (GSE) and somatic sensory (GSA) axons - neuron cell bodies for motor a xons are in the ventral horn gray matter of spinal cord, and the axons for each spinal level combine and exit the anterior spinal cord along paired rows of ventral rootlets anterolaterally, which combine to form the ventral root (anterior root) for each spinal nerve - neurons for sensory nerve fibers are pseudounipolar neurons, with neuron cell bodies in the dorsal root ganglion of the dorsal root (posterior root) of each spinal nerve - after passing through dorsal root ganglion, the dorsal root divides into dorsal rootlets which enter posterior cord along paired rows posterolaterally - note: body sensory receptor cells synapse on sensory fibers of pseudo unipolar neurons, which carry the signals from the receptor cell(s) into spinal cord, including touch, pain and temperature, and proprioception - in this text , afferent fibers of pseudounipolar neurons a re called fibers, up to the neuron cell body, because they are (technically) neither dendrites nor axons, although the are derived from the axon - each spinal nerve ‘begins’ at the union of ventral motor root an d dorsal sensory root, which both arise from spinal cord and come together laterally in the neural foramen, between (below and above) bony pedicles of adjacent vertebral posterior neural arches, exiting the neural foramen as the spinal nerve © ▲spinal cord ► (CNS) - axons are separated by thin fibroconnective endoneurium - axons are bundled together into fascicles, covered by thick membranous fibroconnective perineurium - fascicles are bundled together as the nerve, co vered by thick membranous fibroconnective epineurium