What Are Dermatomes? PNS, 31 Spinal Nerves & Diagnosis

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A dermatome is an area of skin that is supplied by a single spinal sensory nerve. There are 30 dermatomes in the body.

A dermatome is an area of skin that is supplied by a single spinal sensory nerve. Sensory nerves are the nerves that transmit signals from several body parts to the spinal cord. There are 30 dermatomes in the body.

Before understanding the dermatome, it is crucial to know about the spinal nerves. Spinal nerves are part of the peripheral nervous system (PNS). The main function of PNS is to connect the rest of the body to the brain so that the brain can evaluate the inputs it receives.

The body has 31 pairs of spinal nerves and is named and grouped by the region of the spine they are associated with. The different groups of the spinal nerve include:

• Cervical nerves: Eight pairs of these cervical nerves originate from the neck and numbered C1 through C8.
• Thoracic nerves: 12 pairs of thoracic nerves originate from the part of the spine present in the torso and are numbered T1 through T12.
• Lumbar nerves: Five pairs of lumbar spinal nerves come from the part of the spine that makes up the lower back and are designated L1 through L5.
• Sacral nerve: Like the lumbar spinal nerves, there are also five pairs of sacral spinal nerves in the sacrum or pelvic bone.
• Coccygeal nerves: There is a single pair of coccygeal spinal nerves originating from the area of the coccyx or tailbone.

What is the importance of the dermatome?

Dermatome can be useful in diagnosing the following diseases:

• Herpes zoster (shingles): It is a viral infection caused by the varicella-zoster virus. The virus may remain dormant in the nerve roots, causing rash and pain along the corresponding dermatome.
• Lumbar radiculopathy: It refers to a condition where the spinal nerve root gets compressed. It leads to radiating back pain, weakness, and tingling extending down a dermatome.
• Spinal cord trauma: Dermatomes can be used to evaluate and diagnose the exact level of the spinal cord or nerve injury in patients who had an accident.