Myotome

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The term myotome (from the Greek Mys “ muscle ”, tomos “cut”) is used in embryology and neuroanatomy and characterizes a muscle segment .

embryology

In the embryo , the myotome is the muscular urinary segment . During embryonic development, the original vertebrae develop from the mesoderm in the trunk area ( thus ). The skin ( dermatome ) is formed from the dorsolateral part and the precursors of the muscle cells ( myoblasts ) form the deeper cells . These cells are called a myotome . The head muscles arise from the gill arches , the occipital somites and the mesenchyme of the prechordal plate . In the neck area, muscles arise from the longitudinal muscle plate in the neck area, M. sternocleidomastoideus and M. trapezius from the sixth gill arch.

In the trunk area, a myotome is divided into:

  • Epimer : upper area from which the dorsal primary back muscles emerge. It is supplied by the rami dorsales of the spinal nerves .
  • Hypomer : lower area that develops into the three layers of the lateral abdominal wall as well as the dorsally immigrated secondary back muscles and is supplied by the ventral rami of the spinal nerves. The same applies to the limb muscles, which also arise from the hypomeres. On the lower part, a longitudinal muscle cord arises, which develops into the rectus abdominis muscle (where the original segmental origin can still be recognized by the tendinous intersections ) and the ventral neck muscles.

anatomy

As a result of the segmental application of the muscles in the embryo, the muscles in adults also show an assignment to certain vertebrae, more precisely to the spinal nerves of the corresponding spinal cord segment. Anatomically, a myotome is also the musculature that is innervated by a spinal nerve whose motor root cells are located in a spinal cord segment.

Due to the plexus formation of the spinal nerves, each anatomical muscle of the limbs is innervated by several spinal nerves ( plurisegmental innervation ). Therefore, a failure will not cause a spinal nerve root to the total failure of the myotome, but it takes only a partial paralysis ( paresis ) on. If several segments affected or is a Plexusnerv damaged, however, it does a flabby (complete) paralysis ( paralysis ). In the case of nerve root damage, not all muscles of a myotome are equally affected. Muscles that derive their motor innervation mainly from a segment of the spinal cord are called identification muscles . Their functional failure indicates a pathological occurrence in a specific spinal cord segment, which is used to localize damage in clinical neurology.

The afferent tracts of a spinal nerve from the muscles are called the Mackenzie zone . They play a role in the referred pain phenomenon .

See also

Individual evidence

  1. ↑ a b Ulrike Bommas-Ebert, Philipp Teubner, Rainer Voss: Short textbook anatomy and embryology . Georg Thieme, Stuttgart 2006, ISBN 978-3-13-135532-4 , p. 52.
  2. ^ Norbert Ulfig: short textbook embryology . Georg Thieme, Stuttgart, 2009, ISBN 978-3-13-139582-5 , p. 65
  3. ↑ a b Peter Berlit: Clinical Neurology . Springer Science & Business Media, 2nd edition, 2005, ISBN 978-3-540-01982-4 , p. 309
  4. ↑ Henrik Simon: Textbook Chiropractic . Georg Thieme, Stuttgart, 2nd edition 2019, ISBN 978-3-13-241455-6 , p. 31.