A myotome is the group of
muscles that a single
spinal nerve 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 de ...
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 c ...
embryonic development, 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The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail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
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The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail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 ...
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.
See also
*
Dermatome (anatomy)
A dermatome is an area of skin that is mainly supplied by afferent nerve fibres from the dorsal root of any given spinal nerve.
There are 8 cervical nerves (C1 being an exception with no dermatome),
12 thoracic nerves,
5 lumbar nerves and 5 ...
*
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 ...
References
Further reading
*''Neurology Textbook'', edited by Professor L. Sokolva, M.D., D.Sc. 2012,
External links
*
*
* {{EmbryologyUNC, mslimb, 009
Neurology