The nerve roots(?) exit at a level above their respective vertebral bodies in the cervical region (e.g., the C7 nerve root exits at the C6-C7 level) and below their respective vertebral bodies in the thoracic and lumbar regions (e.g., the T1 nerve root exits at the T1-T2 level).
The cervical nerve roots follow a short intraspinal course before exiting.
By contrast, because the spinal cord ends at the vertebral L1 or L2 level, the lumbar nerve roots follow a long intraspinal course and can be injured anywhere from the upper lumbar spine to their exit at the intervertebral foramen. For example, disk herniation at the L4-L5 level can produce not only L5 root compression, but also compression of the traversing S1 nerve root (Fig. 22-3). The lumbar nerve roots are mobile in the spinal canal, but eventually pass through the narrow lateral recess of the spinal canal and intervertebral foramen (Figs. 22-2 and 22-3). Neuroimaging of the spine must include both sagittal and axial views to assess possible compression in either the lateral recess or intervertebral foramen.
The spinal nerves contain a mixture of sensory and motor neurons.
Components of a typical cutaneous nerve. There are two distinct functional categories of axons: primary afferents with cell bodies in the dorsal root ganglion, and sympathetic postganglionic fibers with cell bodies in the sympathetic ganglion.
Primary afferents include those with large-diameter myelinated (Aβ), small-diameter myelinated (Aδ), and unmyelinated (C) axons. All sympathetic postganglionic fibers are unmyelinated.
A 48-year-old man goes to his physician because of pain and paresthesia along the lateral aspect of the leg and the dorsum of the foot. The patient's symptoms suggest impingement of the L5 spinal nerve resulting from a herniated intervertebral disc. The L5 spinal nerve most likely exits between which of the following vertebrae?