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Myotome

Scheme showing the manner in which each vertebral centrum is developed from portions of two adjacent segments. (Myotome labeled in upper right.)

Transverse section of a human embryo of the third week to show the differentiation of the primitive segment. ao. Aorta. m.p. Muscle-plate. n.c. Neural canal. sc. Sclerotome. s.p. cutis-plate. ("Muscle-plate" is an older term for "myotome.")
Latin	myotomus
Gray's	subject #17 80
Carnegie stage	13/14
Precursor	somite
Gives rise to	muscle
Code	TE E5.2.0.0.0.0.6

In vertebrate embryonic development, a myotome is a group of tissues formed from somites. These somites develop into the body wall muscle.

Each myotome divides into a dorsal epaxial part and a ventral hypaxial part.

The myoblasts 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.^[1] It is the motor equivalent of a dermatome.

Each muscle in the body is supplied by a 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.^[2]

The epaxial muscle mass loses its segmental character to form the extensor muscles of the neck and trunk of mammals. In fishes, salamanders, caecilians, and reptiles, 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

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.^[3] 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;^[4]^[5]

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
C8-thumb extension
T1-finger abduction
L2-hip flexion
L3-knee extension
L4-ankle dorsi-flexion
L5-great toe extension
S1-ankle plantar-flexion
S2-knee flexion

References

^ myotome at eMedicine Dictionary
^ Apparelyzed: Myotomes & Dermatomes
^ Magee, David. J (2006). "1". Orthopaedic Physical Assessment (4th ed.). St. Louis: Elsevier. pp. 1–63. ISBN 978-1-4160-3109-3.
^ Magee, David. J (2006). "3". Orthopaedic Physocal Assessment (4th ed.). St. Louis: Elsevier. pp. 121–181. ISBN 978-1-4160-3109-3.
^ Magee, David. J (2009). "9". Orthopaedic Physocal Assessment (4th ed.). St. Louis: Elsevier. pp. 467–566. ISBN 978-1-4160-3109-3.

External links

Embryology at UNSW Notes/skmus7
Embryology at UNSW Notes/week3_6
mslimb-009 — Embryo Images at University of North Carolina

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English Journal

Development of somites, muscle, and skeleton is independent of signals from the wolffian duct.

Krück S, Nesemann J, Scaal M.SourceInstitute of Anatomy II, University of Cologne, Cologne, Germany; Institute of Anatomy and Cell Biology, Department of Molecular Embryology, University of Freiburg, Freiburg, Germany.
Developmental dynamics : an official publication of the American Association of Anatomists.Dev Dyn.2013 Aug;242(8):941-8. doi: 10.1002/dvdy.23986. Epub 2013 Jun 11.
Background: In the vertebrate embryo, skeletal muscle and the axial skeleton arise from the somites. Patterning of the somites into the respective somite compartments, namely dermomyotome, myotome, and sclerotome, depends on molecular signals from neighboring structures, including surface ectoderm,
PMID 23681750

Muscle development and body growth in larvae and early post-larvae of shi drum, Umbrina cirrosa L., reared under different larval photoperiod: muscle structural and ultrastructural study.

Ayala MD, Abellán E, Arizcun M, García-Alcázar A, Navarro F, Blanco A, López-Albors OM.SourceDepartment Anatomía y Anatomía Patológica Comparadas, Anatomía y Embriología Veterinaria, Facultad de Veterinaria, Universidad de Murcia, 30100, Murcia, Spain, mdayala@um.es.
Fish physiology and biochemistry.Fish Physiol Biochem.2013 Aug;39(4):807-27. doi: 10.1007/s10695-012-9742-x. Epub 2012 Nov 4.
Shi drum specimens were maintained under four different photoperiod regimes: a natural photoperiod regime (16L:8D), constant light (24L), equal durations of light and dark (12L:12D) and a reduced number of daylight hours (6L:18D) from hatching until the end of larval metamorphosis. Specimens were th
PMID 23124866

Body wall development in lamprey and a new perspective on the origin of vertebrate paired fins.

Tulenko FJ, McCauley DW, Mackenzie EL, Mazan S, Kuratani S, Sugahara F, Kusakabe R, Burke AC.SourceDepartment of Biology, Wesleyan University, Middletown, CT 06459.
Proceedings of the National Academy of Sciences of the United States of America.Proc Natl Acad Sci U S A.2013 Jul 16;110(29):11899-904. doi: 10.1073/pnas.1304210110. Epub 2013 Jul 1.
Classical hypotheses regarding the evolutionary origin of paired appendages propose transformation of precursor structures (gill arches and lateral fin folds) into paired fins. During development, gnathostome paired appendages form as outgrowths of body wall somatopleure, a tissue composed of somati
PMID 23818600

Japanese Journal

Muscle fiber types, growth and development in the whole myotome of cultured Pacific bluefin tuna Thunnus orientalis

ROY Bimol Chandra,ANDO Masashi,NAKATANI Masahiro,OKADA Tokihiko,SAWADA Yoshifumi,ITOH Tomohiro,TSUKAMASA Yasuyuki
Fisheries science : FS 78(2), 471-483, 2012-03-01
NAID 10030125177

骨格筋分化の分子メカニズム

横山成俊,浅原弘嗣
内分泌・糖尿病・代謝内科 31(5), 486-492, 2010-11
NAID 40018275459

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