A myotome is the group of

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...

s that a single

spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...

innervates. Similarly a dermatome is an area of

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

that a single nerve innervates with sensory fibers. Myotomes are separated by myosepta (singular: myoseptum). In

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...

embryonic development An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

, a myotome is the part of a

somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide ...

that develops into muscle.

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

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 An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to h ...

herniation pressing on the spinal nerve roots.

References

External links

* * * {{EmbryologyUNC, mslimb, 009 Neurology