Lower inset nerve roots

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The dorsal root (sensory) and ventral root (motor) unite within the intervertebral foramina to form the (mixed) spinal nerve (see also Figure 5). The nerve cell bodies for the dorsal root are located in the dorsal root ganglion (DRG). Both the roots and the dorsal root ganglion belong to the peripheral nervous system (PNS) (where the Schwann cell forms and maintains the myelin).

Developmental Perspective

During early development, the spinal cord is the same length as the vertebral canal and the entering/exiting nerve roots correspond to the spinal cord vertebral levels. During the second part of fetal development, the body and the bony spine continue to grow, but the spinal cord does not. After birth, the spinal cord only fills the vertebral canal to the level of L2, the second lumbar vertebra (see also Figure 3). The space below the termination of the spinal cord is the lumbar cistern, filled with cere-brospinal fluid.

Therefore, as the spinal cord segments do not correspond to the vertebral segments, the nerve roots must travel in a downward direction to reach their proper entry/exit level between the vertebra, more so for the lower spinal cord roots (see the photographic view in Figure 2A and Figure 2C). These nerve roots are collectively called the cauda equina, and they are found in the lumbar cistern (see Figure 2A, Figure 2C, and Figure 3).

Clinical Aspect

The four vertebral levels — cervical, thoracic, lumbar, and sacral — are indicated on the left side of the illustration. The spinal cord levels are indicated on the right side. One must be very aware of which reference point — the vertebral or spinal — is being used when discussing spinal cord injuries.

Nerve roots can be anesthetized by injection of a local anesthetic into their immediate vicinity. One of the locations for this is in the epidural space. The sensory nerve roots to the perineal region, which enter the cord at the sacral level, are often anesthetized in their epidural location during childbirth. This procedure requires a skilled anesthetist.

Vertebral levels

Spinal cord levels

Base of skull






Cervical spinal cord section

Cervical spinal cord section




Need Images Cervical Nerve Root

Spinal nerve

Dorsal root ganglion

Spinal nerve

FIGURE 1: Spinal Cord 1 — Longitudinal (Vertebral) View

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  • Columbus
    What does the nerve root on right side of spinal cord do?
    7 years ago

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