Dermatomes: Full Body Image
- A dermatome represents the unilateral area of skin on the body that is innervated by fibers from the sensory portion of a single spinal nerve coming from the spinal cord.
- Each spinal nerve contains spinal roots (anterior and posterior) that come together to form the spinal nerve.
- This spinal nerve has both afferent and efferent nerve fibers that allow for information to travel from the CNS to the effector organs and from the organs back to the CNS. For example, a person will perceive a sensation on the skin in a particular area by sending a signal from that area down the afferent nerve fiber that enters into the posterior (dorsal) root which then enters into the spinal cord. Motor impulses travel from the spinal cord through the anterior (ventral) root and then down efferent nerve fibers along with that spinal nerve to muscles in the periphery.
- Each level of the spinal cord has spinal nerves, but the spinal nerve at C1 lacks any significant afferent input from the skin and thus is the only spinal nerve without any representation as a dermatome.
- Dermatomes are different from myotomes in that myotomes are the fibers from a single spinal nerve that innervate muscles (not skin).
Dermatomes are different from the regions innervated by cutaneous nerves. The palmar aspect for the thumb, index and long finger are all innervated by the median nerve. But the thumb receives primary sensory innervation from the C6 nerve root, while the other two fingers receive sensory innervation from C7.
- Dermatomes can be helpful in determining the origin of visceral pain due to shared embryonic innervation. The pain of a myocardial infarction classically radiates into the lower cervical and upper thoracic dermatomes on the left side.
- Shingles (Herpes Zoster) should be suspected when you see a rash that appears in a dermatomal distribution.