Segmental innervation

Segmental Innervation is a fundamental concept in neurology and anatomy that refers to the specific distribution of the nervous system to the various parts of the body. This distribution is primarily carried out by spinal nerves, which are responsible for transmitting sensory and motor information between the central nervous system and the rest of the body.

Overview

Segmental innervation, also known as dermatomal distribution, is the area of skin supplied by a single spinal nerve. Each spinal nerve, except for the first cervical spinal nerve (C1), supplies a specific and predictable area of skin. The pattern of distribution resembles a series of horizontal stripes, with some overlap with the areas above and below.

Spinal Nerves and Segmental Innervation

Spinal nerves are part of the peripheral nervous system and are formed by the combination of the anterior and posterior roots of the spinal cord. There are 31 pairs of spinal nerves, each of which is named and numbered according to the region and level of the spinal cord from which it exits.

The spinal nerves are grouped as follows:

• 8 cervical (C1-C8)
• 12 thoracic (T1-T12)
• 5 lumbar (L1-L5)
• 5 sacral (S1-S5)
• 1 coccygeal (Co)

Each spinal nerve innervates a particular segment of the body. The segmental distribution of these nerves is as follows:

• Cervical nerves (C1-C4) innervate the neck, back of the head, and the upper part of the shoulders.
• Cervical nerves (C5-T1) innervate the upper limbs.
• Thoracic nerves (T1-T12) innervate the thorax and abdomen.
• Lumbar and sacral nerves (L1-S5) innervate the lower limbs.
• The coccygeal nerve (Co) innervates the skin over the coccyx.

Clinical Significance

Understanding segmental innervation is crucial in the clinical setting, particularly in the fields of anesthesiology, neurology, and physical therapy. It allows clinicians to determine the level of potential spinal cord injury by examining the areas of lost sensation or motor function.

For example, a patient with a loss of sensation in the area innervated by the T1 spinal nerve may have a spinal cord injury at the T1 level. Similarly, a patient with weakness or paralysis in the muscles innervated by the L5 spinal nerve may have a spinal cord injury at the L5 level.

See Also

• Dermatome (anatomy)
• Myotome
• Peripheral nervous system
• Spinal cord