Myotome
Encyclopedia
In vertebrate
embryonic development
, a myotome is a group of tissues formed from somite
s that develop into the body wall muscle.
Each myotome divides into a dorsal
epaxial
part and a ventral
hypaxial
part.
The myoblast
s from the hypaxial division form the muscles of the thoracic and anterior abdominal walls.
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.
The epaxial muscle mass loses its segmental character to form the extensor
muscles of the neck and trunk of mammals. In fish
es, salamander
s, caecilian
s, and reptile
s, the body musculature remains segmented as in the embryo, though it often becomes folded and overlapping, with epaxial and hypaxial masses divided into several distinct muscle groups.
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.
Myotome distributions of the upper and lower extremity are as follows;
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
embryonic development
Embryogenesis
Embryogenesis is the process by which the embryo is formed and develops, until it develops into a fetus.Embryogenesis starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote...
, a myotome is a group of tissues formed from somite
Somite
A somite is a division of the body of an animal. In vertebrates this is mainly discernible in the embryo stage; in arthropods it is a characteristic of a hypothetical ancestor.- In vertebrates :...
s that develop into the body wall muscle.
Each myotome divides into a dorsal
Dorsum (biology)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
epaxial
Epaxial and Hypaxial muscles
Trunk muscles can be broadly divided into hypaxial muscle, which lie ventral to the horizontal septum of the vertebrae and epaxial muscles, which lie dorsal to the septum. Hypaxial muscles include some vertebral muscles, the diaphragm, the abdominal muscles, and all limb muscles...
part and a ventral
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
hypaxial
Epaxial and Hypaxial muscles
Trunk muscles can be broadly divided into hypaxial muscle, which lie ventral to the horizontal septum of the vertebrae and epaxial muscles, which lie dorsal to the septum. Hypaxial muscles include some vertebral muscles, the diaphragm, the abdominal muscles, and all limb muscles...
part.
The myoblast
Myoblast
A myoblast is a type of embryonic progenitor cell that gives rise to muscle cells .The muscle cells can be skeletal muscle, smooth muscle, and cardiac muscle....
s from the hypaxial division form the muscles of the thoracic and anterior abdominal walls.
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.
The epaxial muscle mass loses its segmental character to form the extensor
Extension (kinesiology)
In kinesiology, extension is a movement of a joint that results in increased angle between two bones or body surfaces at a joint. Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extending the flexed elbow. Straightening of...
muscles of the neck and trunk of mammals. In fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es, salamander
Salamander
Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s, caecilian
Caecilian
The caecilians are an order of amphibians that superficially resemble earthworms or snakes. They mostly live hidden in the ground, making them the least familiar order of amphibians. All extant caecilians and their closest fossil relatives are grouped as the clade Apoda. They are mostly...
s, and reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s, the body musculature remains segmented as in the embryo, though it often becomes folded and overlapping, with epaxial and hypaxial masses divided into several distinct muscle groups.
Clinical Significance
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 isometricIsometric
The term isometric comes from the Greek for "having equal measurement".isometric may mean:* Isometric projection , a method for the visual representation of three-dimensional objects in two dimensions; a form of orthographic projection, or more specifically, an axonometric projection.* Isometry and...
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
Intervertebral disc
Intervertebral discs lie between adjacent vertebrae in the spine. Each disc forms a cartilaginous joint to allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together.-Structure:...
herniation pressing on the spinal nerve roots.
Myotome distributions of the upper and lower extremity are as follows;
- C1Cervical spinal nerve 1The cervical spinal nerve 1 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 1 .Muscles innervated by this nerve are:*Geniohyoid muscle- through Hypoglossal nerve...
/C2Cervical spinal nerve 2The cervical spinal nerve 2 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 2 ....
-neck flexion/extension - C3Cervical spinal nerve 3The cervical spinal nerve 3 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 3 ....
-neck lateral flexion - C4Cervical spinal nerve 4The cervical spinal nerve 4 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 4 .Its control of the thoracic diaphragm has inspired a medical mnemonic: "Cut C4, breathe no more."...
-shoulder elevation - C5Cervical spinal nerve 5The cervical spinal nerve 5 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 5 ....
-shoulder abduction - C6Cervical spinal nerve 6The cervical spinal nerve 6 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 6 ....
-elbow flexion/wrist extension - C7Cervical spinal nerve 7The cervical spinal nerve 7 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 7 ....
-elbow extension/wrist flexion - C8Cervical spinal nerve 8The cervical spinal nerve 8 is a spinal nerve of the cervical segment.It originates from the spinal column from below the cervical vertebra 7 .- Innervation :...
-thumb extension - T1Thoracic spinal nerve 1The thoracic spinal nerve 1 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 1 ....
-finger abduction - L2Lumbar spinal nerve 2The lumbar spinal nerve 2 is a spinal nerve of the lumbar segment..It originates from the spinal column from below the lumbar vertebra 2 .-Muscles:...
-hip flexion - L3Lumbar spinal nerve 3The lumbar spinal nerve 3 is a spinal nerve of the lumbar segment..It originates from the spinal column from below the lumbar vertebra 3 .-Muscles:...
-knee extension - L4Lumbar spinal nerve 4The lumbar spinal nerve 4 is a spinal nerve of the lumbar segment..It originates from the spinal column from below the lumbar vertebra 4 .-Muscles:...
-ankle dorsi-flexion - L5Lumbar spinal nerve 5The lumbar spinal nerve 5 is a spinal nerve of the lumbar segment..It originates from the spinal column from below the lumbar vertebra 5 .-Muscles:...
-great toe extension - S1Sacral spinal nerve 1The sacral spinal nerve 1 is a spinal nerve of the sacral segment..It originates from the spinal column from below the 1st body of the sacrum -Muscles:...
-ankle plantar-flexion - S2Sacral spinal nerve 2The sacral spinal nerve 2 is a spinal nerve of the sacral segment..It originates from the spinal column from below the 2nd body of the sacrum -Muscles:...
-knee flexion