Dermatome (anatomy)

The dermatome (from Greek δέρμα derma "skin" and τομή Tome " ( From ) cut " ) is that of a spinal nerve ( spinal nerves ) sensitive innervated segmental skin area.

Embryological bases

During the segmentation of the embryo arise in the trunk region of the paraxial mesoderm, the side of the neural tube and the notochord, the first somites ( So ). From the dorsolateral part of the skin forms. This system is called a dermatome. As a result of these segmental origin of individual skin areas there is also a segmental assignment to the corresponding spinal nerves.

Anatomy

Even in adults, this segmental assignment of the spinal nerves is maintained to appropriate skin areas. The cell bodies of these neurons are sensitive outside the spinal cord in the spinal ganglion ( spinal ganglion ). However, there is an overlap of the skin areas of the individual spinal nerves. In an injury to a spinal nerve, therefore, occurs not a complete loss of sensitivity in the corresponding dermatome. The overlap should be pronounced for the perception of pain and temperature stimuli less than of tactile stimuli. Due to the overlap often occurs only in case of failure of two adjacent segments to a marked sensory loss.

Autonomous region

In the area of the neck and in the lumbar area cross the ventral rami of the spinal nerves form plexuses ( plexus ) of:

• Cervical plexus ( cervical plexus )
• Armgeflecht ( brachial plexus )
• Loins and braid ( lumbosacral plexus )

Due to the fiber exchange in these braids arise sg Plexusnerven. This result, in most cases axons of several segments. An area of ​​skin that is innervated sensitive exclusively by a particular nerve, also called autonomous territory of this nerve. Damage to the nerve typically leads to a loss of sensitivity in its autonomous region.

Selected autonomous areas:

• Ulnar nerve: pinky
• Median nerve: end members of the index and middle finger
• Radial nerve: above the metacarpal bone of the thumb (but not constant )
• Deep fibular nerve: first interdigital space
• Tibial nerve: sole and heel

Transferred pain

Since viszerosensible sensations on the spinal nerves are transmitted ( viscera, " entrails ", " internal organs " ), but these can not be assigned to an exact location due to lack of experience of the relevant region of the cerebral cortex, these pains appropriate by the cerebrum (incorrectly) sensitive skin areas are, usually assigned to the same spinal nerves, such as shoulder pain in Oberbauchperitonitis. In diseases of the internal organs as a hypersensitivity to external stimuli may in a particular area of ​​skin, adjust the so-called Head's zone. This phenomenon is in diagnostics as a head- zone sample studied ( also Kalchschmidt sample). It can also be referred pain in the muscles ( myotome ) of the corresponding segment occur ( Mackenzie zone). An example of this is pain in the left arm during a heart attack.

The Head'sche zone (also Head Zone), named after the English neurologist Sir Henry Head ( 1861-1940 ) is defined as the area of ​​skin where due to the articulated body structure ( → metamerism ) a running via the corresponding spinal cord segment cross connection between the somatic and the autonomic nervous system is composed. This area are associated with specific internal organs, see the following table. The Head'sche zone that is associated with a particular organ, may extend over several dermatomes, but has a significant reflex maximum point. An irritation of the associated internal organ can have a reflex viscerocutaneous a mostly equilateral pain zone result have ( Hyperalgesiezone ). This phenomenon is called referred pain. The pain may u.U. on neighboring segments or the entire half of the body spread ( generalization ). To influence the internal organs can be a reversal of the reflex action (→ reflex reversal) be harnessed by certain skin zones are mechanically, thermally or pharmacologically affected. This method is called reflex therapy ( → kutiviszeraler reflex).