Myotome

Myotome is a group of muscles innervated from a single spinal segment. The term myotome is also used to describe the muscles served by a single nerve root. It is the motor equivalent of a dermatome. Each muscle in the body is supplied by a particular level or segment of the spinal cord and by its corresponding spinal nerve. The muscle and its nerve make up a myotome.

Myotome testing can be an integral part of neurological examination as each nerve root coming from the spinal cord supplies a specific group of muscles. Testing of myotomes, in the form of isometric resisted muscle testing, provides the clinician with information about the level in the spine where a lesion may be present. During myotome testing, the clinician is looking for muscle weakness of a particular group of muscles. Results may indicate lesion to the spinal cord nerve root, or intervetebral disc herniation pressing on the spinal nerve roots.

Myotome distributions of the upper and lower extremity are as follows:

C3,4 and 5 supply the diaphragm (the large muscle between the chest and the belly that we use to breath).
C5 also supplies the shoulder muscles and the muscle that we use to bend our elbow .
C6 is for bending the wrist back.
C7 is for straightening the elbow.
C8 bends the fingers.
T1 spreads the fingers.
T1 –T12 supplies the chest wall & abdominal muscles.
L2 bends the hip.
L3 straightens the knee.
L4 pulls the foot up.
L5 wiggles the toes.
S1 pulls the foot down.
S3,4 and 5 supply the bladder. bowel and sex organs and the anal and other pelvic muscles.

*for further reading, you may go to this website:
           http://www.whiplash101.com/2009/11/myotomes-dermatomes-pain-help/