Musculature: Functional Groups

2 Musculature: Functional Groups


2.1 The Muscles of the Trunk Wall: Their Origin and Function


Overview of the Trunk Wall Muscles


The muscles of the trunk wall in the strict sense consist of the intrinsic back muscles and the muscles of the chest and abdominal wall. In the broad sense, they include the muscles of the pelvic floor (which form the inferior boundary of the abdominopelvic cavity) and the diaphragm (which separates the thoracic and abdominal cavities). Besides the muscles of the trunk wall, the back and thorax also contain muscles of the shoulder girdle and upper limb that migrated to the trunk during the course of development (nonintrinsic back and thoracic muscles). Examples are the thoracohumeral muscles anteriorly, the spinohumeral muscles laterally and posteriorly, and the spinocostal muscles. Other muscles that have migrated to the trunk, such as the trapezius, are derived from the mesenchyme of the branchial arches (branchial musculature). They are innervated by cranial nerves (the trapezius by the accessory nerve) and were incorporated secondarily into the trunk wall (see p. 300 ff).


A Trunk wall muscles in the strict sense





















Intrinsic back muscles

Lateral tract


Sacrospinal system


Iliocostalis


Longissimus


Spinotransverse system


Splenius


Intertransverse system


Intertransversarii


Levatores costarum


Medial tract


Spinal system


Interspinales


Spinalis


Transversospinal system


Rotatores breves and longi


Multifidus


Semispinalis


Short nuchal and craniovertebral joint muscles (suboccipital muscles)


Rectus capitis posterior major


Rectus capitis posterior minor


Obliquus capitis superior


Obliquus capitis inferior


Prevertebral neck muscles (belong topographically to the group of deep neck muscles but act mainly on the cervical spine)


Longus capitis


Longus colli


Rectus capitis lateralis


Rectus capitis anterior


Muscles of the thoracic cage and wall


Intercostal muscles


Transversus thoracis


Subcostal muscles


Scalene muscles (belong topographically to the group of deep neck muscles but are functionally related to thoracic breathing)


Muscles of the abdominal wall


Anterolateral abdominal muscles


External oblique


Internal oblique


Transversus abdominis


Anterior (straight or strap) abdominal muscles


Rectus abdominis


Pyramidalis


Posterior (deep) abdominal muscles


Quadratus lumborum


Psoas major (belongs functionally to the hip muscles, see p. 482)


B Trunk wall muscles in the broad sense














Muscles of the pelvic floor and perineum


Pelvic diaphragm


Levator ani muscle


Puborectalis


Pubococcygeus


Iliococcygeus


Coccygeus


Deep perineal muscles


Deep transverse prineal (in male)


External urethral sphincter


Compressor urethra (in female)


Urethrovaginal sphincter (in female)


Superficial perineal muscles


Superficial transverse perineal


Bulbospongiosus


Ischiocavernosus


External anal sphincter


Diaphragm


Costal part


Lumbar part (crura)


Sternal part


C Muscles that migrated secondarily to the trunk wall (described in the Upper Limb unit, p. 240)






















Spinocostal muscles (see also p. 166)


Serratus posterior superior


Serratus posterior inferior


Spinohumeral muscles between the trunk and shoulder girdle


Rhomboid major and minor


Levator scapulae


Serratus anterior


Subclavius


Pectoralis minor


Trapezius


Spinohumeral muscles between the trunk and arm


Latissimus dorsi


Thoracohumeral muscles


Pectoralis major


* The suboccipital muscles in the strict sense are the short or deep nuchal muscles that are counted among the intrinsic back muscles (because they are innervated by a posterior ramus). The rectus capitis anterior and lateralis muscles are not classified as intrinsic back muscles because they are innervated by anterior rami, even though they are also suboccipital in their location.


Origin of the Trunk Wall Muscles


The striated muscles of the trunk wall (including the muscles of the diaphragm and pelvic floor), like the limb muscles, develop embryologically from the myotomes of the somites (see p. 6) and are therefore called the somatic muscles. In all, approximately 42 to 44 pairs of segmental somites are formed in the paraxial mesoderm between the 20th and 30th day of development. Five occipital, 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 8 to 10 coccygeal somites are formed in a craniocaudal sequence (see D). Some of these somites regress with further development, particularly the first occipital somites and most of the coccygeal somites, so that the number of original somites is greater than the number of subsequent vertebral segments. The boundary between the head and neck runs through the fifth pair of occipital somites. At the end of the sixth week of development, the somite myotomes migrate in the dorsoventral direction and become separated into a dorsal part (epimere or epaxial muscles) and a ventral part (hypomere or hypaxial muscles) (E). While the epaxial muscles develop into intrinsic (local) back muscles and retain their original location, the hypomere develops into the anterolateral muscles of the chest and abdominal wall and the limb musculature (F). As the myotomes become segregated, the spinal nerves undergo a corresponding division into a dorsal (posterior) ramus for the epaxial muscles and a ventral (anterior) ramus for the hypaxial muscles (see Ea). The original segmental (metameric) arrangement of the trunk muscles mostly disappears with further development. It persists only in the deep layers of the intrinsic back muscles (e.g., the rotator, interspinal, and intertransverse muscles) and the thoracic muscles (e.g., the internal and external intercostal muscles), while the superficial portions of the myotomes fuse together to form long, continuous muscles (“polymerization”) in which only the neurovascular supply still exhibits the original segmental arrangement (see F).



image

D Somites in a 5-week-old human embryo


Right lateral view. The somites formed from the paraxial mesoderm are classified as preotic (shown in blue and green) or postotic (shown in red), meaning that they are located cranial or caudal to the ear rudiment. The somatic muscles develop from postotic somites. Segmentation into different somites is not observed in the preotic region, which contains the rudiments for the branchiogenic pharyngeal arch muscles and the extraocular muscles. The structures in this region are innervated by cranial nerves (after Boyd, Hamilton, and Mossmann, quoted in Starck).



image

E Transverse sections through a 6-week-old human embryo


a Transverse section at the level of a limb bud.


b Transverse section through the abdominal wall.


Muscle precursor cells with replicative capacity located at the level of the limb buds migrate from the myotomes into the limb buds, and the myotome that remains in these regions develops into intrinsic back muscles. With further growth of the limb bud, the muscle tissue differentiates into a dorsal rudiment (blastema) for the extensor muscles and a ventral rudiment for the flexor muscles of the upper and lower limbs (see p. 20). As in the hypomere, the limb muscles are innervated by ventral (anterior) spinal nerve rami (brachial plexus and lumbosacral plexus, see pp. 362 and 536).


Note the different innervation of the epaxial muscles (dorsal [posterior] ramus) and hypaxial muscles (ventral [anterior] ramus).



image

F Diagram of the principal muscle groups in an 8-week-old human embryo


Right lateral view. Red = somatic muscles, blue = branchiogenic (branchial arch) muscles, green = extraocular muscles (after Boyd, Hamilton, and Mossmann, quoted in Starck).


2.2 The Intrinsic Back Muscles: Lateral Tract



image

A Lateral tract: schematic of the sacrospinal system


a Iliocostalis muscles.


b Longissimus muscles.



image

B Lateral tract: schematic of the spinotransverse and intertransverse systems


a Splenius muscles.


b Intertransversarii and levatores costarum muscles.



































Iliocostalis muscles (*see p. 147, opposite, lower right)


Origin:


Iliocostalis lumborum: sacrum, iliac crest, superficial layer of the thoracolumbar fascia


Iliocostalis thoracis: seventh to twelfth ribs


Iliocostalis cervicis: third to seventh ribs


Insertion:


Iliocostalis lumborum: sixth to twelfth ribs, deep layer of thoracolumbar fascia, transverse processes of upper lumbar vertebrae


Iliocostalis thoracis: first to sixth ribs


Iliocostalis cervicis: transverse processes of C4–C6 vertebrae


Action:


Entire muscle: bilateral contraction extends the spine, unilateral contraction bends the spine laterally to the same side.


Innervation:


Lateral branches of posterior rami of spinal nerves C8–L1


Longissimus muscles


Origin:


Longissimus thoracis: sacrum, iliac crest (common tendon of origin with iliocostalis), spinous processes of lumbar vertebrae, transverse processes of lower thoracic vertebrae


Longissimus cervicis: transverse processes of T1–T6 vertebrae


Longissimus capitis: transverse processes of T1–T3 vertebrae and transverse and articular processes of C4–C7 vertebrae


Insertion:


Longissimus thoracis: second to twelfth ribs, costal processes of lumbar vertebrae, transverse processes of thoracic vertebrae


Longissimus cervicis: transverse processes of C2–C5 vertebrae


Longissimus capitis: mastoid process of temporal bone


Action:


Entire muscle: bilateral contraction extends the spine, unilateral contraction bends the spine laterally to the same side.


Longissimus capitis: bilateral contraction extends the head, unilateral contraction flexes and rotates the head to the same side.


Innervation:


Lateral branches of posterior rami of spinal nerves C1–L5














































Splenius muscles


Origin:


Splenius cervicis: spinous processes of the T3–T6 vertebrae


Splenius capitis: nuchal ligament, spinous processes of the C7–T3 vertebrae


Insertion:


Splenius cervicis: transverse processes of C1 and C2


Splenius capitis: lateral superior nuchal line, mastoid process


Action:


Entire muscle: bilateral contraction extends the cervical spine and head, unilateral contraction flexes and rotates the head to the same side.


Innervation:


Lateral branches of dorsal rami of spinal nerves C1–C6


Intertransversarii


Origin and insertion:


Intertransversarii mediales lumborum: course between adjacent mammillary processes of all lumbar vertebrae


Intertransversarii laterales lumborum: course between adjacent costal processes of all lumbar vertebrae


Intertransversarii posteriores cervicis: course between adjacent posterior tubercles of the C2–C7 vertebrae


Intertransversarii anteriores cervicis: course between adjacent anterior tubercles of the C2–C7 vertebrae


Action:


Bilateral contraction stabilizes and extends the cervical and lumbar spine.


Unilateral contraction bends the cervical and lumbar spine laterally to the same side.


Innervation:


Posterior rami of the spinal nerves for intertransversarii mediales lumborum, intertransversarii laterales lumborum, and intertransversarii posteriores cervicis; anterior rami of the spinal nerves for intertransversarii anteriores cervicis


Levatores costarum


Origin:


Levatores costarum breves: transverse processes of the C7 and T1–T11 vertebrae


Levatores costarum longi: transverse processes of the C7 and T1–T11 vertebrae


Insertion:


Levatores costarum breves: costal angle of the next lower rib


Levatores costarum longi: costal angle of second lower rib


Action:


Bilateral contraction extends the thoracic spine.


Unilateral contraction bends the thoracic spine to the same side, rotates it to the opposite side.


Innervation:


Posterior rami of the spinal nerves




image

D Lateral tract of the intrinsic back muscles: the spinotransverse system (splenius muscles) and intertransverse system (intertransversarii and levatores costarum muscles)


* The schematic muscle diagrams with accompanying tables on p. 146 are intended to give a systematic overview of the muscles and their actions. The drawings on the right-hand page are intended to display the muscles as they would appear in a dissection. Not all the structures listed in the tables on p. 146 are labeled in the drawings above, as they are not all visible in the views shown.


2.3 The Intrinsic Back Muscles: Medial Tract



image

A Medial tract of the intrinsic back muscles: schematic of the spinal system


The interspinales and spinalis muscles.
































Interspinales muscles


Origin and insertion:


Interspinales cervicis: course between the spinous processes of adjacent cervical vertebrae


Interspinales lumborum: course between the spinous processes of adjacent lumbar vertebrae


Action:


Extends the cervical and lumbar spine


Innervation:


Posterior rami of the spinal nerves


Spinalis muscles


Origin:


Spinalis thoracis: lateral surface of the spinous processes of the T10–T12 and L1–L3 vertebrae


Spinalis cervicis: spinous processes of the C5–C7 and T1–T2 vertebrae


Insertion:


Spinalis thoracis: lateral surface of the spinous processes of the T2–T8 vertebrae


Spinalis cervicis: spinous processes of the C2–C5 vertebrae


Action:


Bilateral contraction extends the cervical and thoracic spine.


Unilateral contraction bends the cervical and thoracic spine to the same side.


Innervation:


Posterior rami of the spinal nerves



image

B Medial tract of the intrinsic back muscles: schematic of the transversospinal system


a Rotatores breves and longi.


b Multifidus.


c Semispinalis.
































Rotatores breves and longi


Origin and insertion:


Rotatores breves: from transverse process of thoracic vertebrae to spinous process of the next higher vertebra


Rotatores longi: from transverse process of thoracic vertebrae to spinious process of the vertebra two levels higher


Action:


Bilateral contraction extends the thoracic spine.


Unilateral contraction rotates it to the opposite side.


Innervation:


Posterior rami of the spinal nerves


Semispinalis muscles


Origin:


Semispinalis thoracis: transverse processes of the T6–T12 vertebrae


Semispinalis cervicis: transverse processes of the T1–T6 vertebrae


Semispinalis capitis: transverse processes of the C3–T6 vertebrae


Insertion:


Semispinalis thoracis: spinous processes of the C6–T4 vertebrae


Semispinalis cervicis: spinous processes of the C2–C5 vertebrae


Semispinalis capitis: occipital bone between the superior and inferior nuchal lines


Action:


Bilateral contraction extends the thoracic spine, cervical spine, and head (stabilizes the craniovertebral joints).


Unilateral contraction bends the head, cervical spine, and thoracic spine to the same side and rotates them to the opposite side.


Insertion:


Posterior rami of the spinal nerves


Jul 25, 2021 | Posted by in ANATOMY | Comments Off on Musculature: Functional Groups

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