Dermatome (anatomy)
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A dermatome is an area of skin that is mainly supplied by a single spinal nerve. There are eight cervical nerves, twelve thoracic nerves, five lumbar nerves and five sacral nerves. Each of these nerves relays sensation (including pain) from a particular region of skin to the brain.
Along the thorax and abdomen the dermatomes are like a stack of discs forming a human, each supplied by a different spinal nerve. Along the arms and the legs, the pattern is different: the dermatomes run longitudinally along the limbs. Although the general pattern is similar in all people, the precise areas of innervation are as unique to an individual as fingerprints.
A similar area innervated by peripheral nerves is called a peripheral nerve field.
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[edit] Clinical significance
Dermatomes are useful in neurology for finding the site of damage to the spine. Because painful dermatomes are symptoms, not causes, of the underlying problem, surgery should never be determined by a pain. Aching in a dermatomic area indicates a lack of oxygen to the nerve as occurs in inflammation somewhere along the path of the nerve. Pain in a dermatomic area (that is not accompanied by heat, as would occur in infection) is indicative of a referral pattern from some other source. This "other source" will not be painful until it is palpated and is usually found (according to Head[citation needed]) on the left side of the vertebral column at the level or one level above or below the dermatomal region of the experienced pain. This information is important in the clinical relevance of dermatomes in that dermatomes are not good measures of dysfunction (that is, non-pathological states as experienced by most people in chronic pain). A compressed spinal nerve, for example, will show as a loss of motor function (i.e. as loss of muscle mass in a proscribed area and/or as an inability to use the muscle against gravity elsewhere on the body) but may or may not exhibit symptoms in the dermatomic area covered by the compressed nerve.
Viruses that infect spinal nerves such as Herpes zoster infections (shingles), can reveal their origin by showing up as a painful dermatomic area. Herpes zoster, a virus that is dormant in the dorsal root ganglion, migrates along the spinal nerve to affect only the area of skin served by that nerve. Symptoms are usually unilateral but in the immune suppressed, they are more likely to become bilateral and symmetrical, meaning that the virus is present in both ganglia of a dorsal root ganglion pair.
[edit] Important dermatomes and anatomical landmarks
- C2 - posterior half of the skull cap
- C3 - area correlating to a high turtle neck shirt
- C4 - area correlating to a low-collar shirt
- C6 - (radial nerve) 1st digit (thumb)
- C7 - (median nerve) 2nd and 3rd digit
- C8 - (ulnar nerve) 4th and 5th digit, also the funny bone
- T4 - nipples.
- T5 - Inframammary fold.
- T6/T7 - xiphoid process.
- T10 - umbilicus (important for early appendicitis pain)
- T12 - pubic bone area.
- L1 - inguinal ligament
- L4 - includes the knee caps
- S2/S3 - genitalia
[edit] Additional images
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Distribution of cutaneous nerves. Ventral aspect. |
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Distribution of cutaneous nerves. Dorsal aspect. |
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Cutaneous nerves of right upper extremity. |
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Diagram of segmental distribution of the cutaneous nerves of the right upper extremity. |
[edit] See also
[edit] External links
- Hand kinesiology at UK nerves/dermatome.htm
- Diagram "Adult Dermatome", The New York Timesca:Dermàtom
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