Dermatomes and Myotomes

Dermatomes :

Area of skin that is supplied by afferent nerve fiber from a single dorsal root of a spinal nerve which form apart of a spinal nerve.

There are 8 cervical nerves

(C1 being an exception with no dermatomes)

12 Thoracic Nerves

5 Lumbar Nerves

5 Sacral Nerves

Uses:

Useful to help localize neurologic level, particularly in racidulopathy. Effacement of Spinal nerve may or may not exhibit symptoms ina dermatic area covered by compressed nerve roots in addition to weakness, deep tendon reflex loss.

Causes and Symptoms :

Area of skin supplied by Sensory neuron thatarises from spinal nerve ganglion.

Symptoms that are followed by Dermatomes (like pain, or a rash) may include a pathology that involves the related nerve roots.

For example : Somatic dysfunction of a spine or viral infection.

Testing :

Testing of dermatomes is a part of neurological examination looking for radiculopathy as sensation changes with in a special dermatome may help in determine the pathological disc level.

Testing is done with pin or cotton wool. Ask patient to close eyes and give therapist feedback regarding various stimuli.

Testing should be done on specific dermatomes and should be compared bilaterally.

Myotomes :

Myotomes is a group of muscles innervated by the ventral root a single spinal nerve. The term is based on the combination of two ancient Greek roots, myo ( muscles) and tomes ( cutting). Like spinal nerves myotomes are organised into segments because they share a common origin.

Uses:

They can determine if damage happens to spinal cord and at which level the damage occurred.

Testing :

Muscle range is checked to know about Muscular weakness.

Are myotomes and dermatomes same?

A myotome is a group of muscles that a single spinal nerve innervates. Similarly a dermatomes is area of skin that a single nerve innervates. In vertebra embryonic development, a myotome is a part of a somite that developes into muscles.

Written by :Dr Neha Asif

Young’s physiotherapist assiosiation