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. In vertebrate embryonic development, a myotome is the part of a somite that develops into the muscles.
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. Myotomes are separated by myosepta.
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
- C1/C2: neck flexion/extension
- C3: neck lateral flexion
- C4: shoulder elevation
- C5: shoulder abduction
- C6: elbow flexion/wrist extension
- C7: elbow extension/wrist flexion/finger extension
- C8: finger flexion
- T1: finger abduction
- L2: hip flexion
- L3: knee extension
- L4: ankle dorsi-flexion
- L5: great toe extension
- S1: ankle plantar-flexion/ankle eversion/hip extension
- S2: knee flexion
- S3–S4: anal wink
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.
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