myotome myotome a myotome is the group of muscles that a single spinal nerve innervates. similarly a dermatome is an area of skin that a single nerve innervates with sensory fibers. myotomes are separated by myosepta (singular: myoseptum). in vertebrate embryonic development, a myotome is the part of a somite that develops into muscle. this article is about anatomical myotomes. for myotomes in developmental biology and embryology, see myotome (embryology). structure the anatomical term myotome which describes the muscles served by a spinal nerve root, is also used in embryology to describe that part of the somite which develops into the muscles. in anatomy the myotome is the motor equivalent of a dermatome. function each muscle in the body is supplied by one or more levels or segments of the spinal cord and by their corresponding spinal nerves. a group of muscles innervated by the motor fibres of a single nerve root is known as a myotome. list of myotomes myotome distributions of the upper and lower extremity are as follows; c1/c2: neck flexion/extension c3: lateral neck flexion c4: shoulder elevation c5: shoulder abduction c6: elbow flexion/wrist extension c7: elbow extension/wrist flexion c8: thumb extension t1: finger abduction & adduction l1/l2: hip flexion l3: knee extension l4: ankle dorsi-flexion l5: great toe extension s1: hip extension/ankle plantar-flexion/ankle eversion s2: knee flexion s3–s4: anal wink clinical significance in humans 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 intervertebral disc herniation pressing on the spinal nerve roots.