Muscles of the Back.Pdf
Muscles of the Back The muscles of the back may be divided into three groups:
The superficial muscles connected with the shoulder girdle. The intermediate muscles involved with movements of the thoracic cage. The deep muscles or postvertebral muscles belonging to the vertebral column
The superficial muscles of the back - Muscles Connecting the Upper Limb to the Vertebral Column Nerve Muscle Origin Insertion Nerve Supply Rootsa Action Trapezius Occipital bone, ligamentum Upper fibers into lateral Spinal part of XI cranial Upper fibers elevate the nuchae, spine of seventh third of clavicle; middle accessory nerve nerve scapula; middle fibers pull cervical vertebra, spines of and lower fibers into (motor) and C3 and 4 (spinal scapula medially; lower all thoracic vertebrae acromion and spine of (sensory) part) fibers pull medial border of scapula scapula downward Latissimus Iliac crest, lumbar fascia, Floor of bicipital groove Thoracodorsal nerve C6, 7, 8, Extends, adducts, and dorsi spines of lower six thoracic of humerus medially rotates the arm vertebrae, lower three or four ribs, and inferior angle of scapula Levator Transverse processes of first Medial border of C3 and 4 and dorsal C3, 4, 5 Raises medial border of scapulae four cervical vertebrae scapula scapular nerve scapula Rhomboid Ligamentum nuchae and Medial border of Dorsal scapular nerve C4, 5 Raises medial border of minor spines of seventh cervical scapula scapula upward and and first thoracic vertebrae medially Rhomboid Second to fifth thoracic Medial border of Dorsal scapular nerve C4, 5 Raises medial border of major spines scapula scapula upward and medially a The predominant nerve root supply is indicated by boldface type. The intermediate muscles of the back Muscle Origin Insertion Action Innervation Artery Notes serratus ligamentum nuchae, ribs 2-5, elevates branches of the posterior a respiratory muscle, it posterior spines of vertebrae lateral to the upper ventral primary intercostal aa. 1- receives ventral ramus superior C7 and T1-T3 the angles ribs rami of spinal 4 innervation; embryonically nerves T1-T4 related to the intercostal muscles, not the deep back mm. serratus thoracolumbar ribs 9-12, pulls branches of the lowest posterior a respiratory muscle, it posterior fascia, spines of lateral to down ventral primary intercostal a., receives ventral ramus inferior vertebrae T11-T12 the angles lower rami of spinal subcostal a., innervation; embryonically and L1-L2 ribs nerves T9-T12 first two lumbar related to the intercostal aa. muscles, not the deep back mm. Deep Muscles of the Back (Postvertebral Muscles) In the standing position, the line of gravity passes through the odontoid process of the axis, behind the centers of the hip joints, and in front of the knee and ankle joints. It follows that when the body is in this position, the greater part of its weight falls in front of the vertebral column. It is, therefore, not surprising to find that the postvertebral muscles of the back are well developed in humans. The postural tone of these muscles is the major factor responsible for the maintenance of the normal curves of the vertebral column. The deep muscles of the back form a broad, thick column of muscle tissue, which occupies the hollow on each side of the spinous processes of the vertebral column. They extend from the sacrum to the skull. It must be realized that this complicated muscle mass is composed of many separate muscles of varying length. Each individual muscle may be regarded as a string, which, when pulled on, causes one or several vertebrae to be extended or rotated on the vertebra below. Because the origins and insertions of the different groups of muscles overlap, entire regions of the vertebral column can be made to move smoothly. The spines and transverse processes of the vertebrae serve as levers that facilitate the muscle actions. The muscles of longest length lie superficially and run vertically from the sacrum to the rib angles, the transverse processes, and the upper vertebral spines. The muscles of intermediate length run obliquely from the transverse processes to the spines. The shortest and deepest muscle fibers run between the spines and between the transverse processes of adjacent vertebrae.
The deep muscles of the back may be classified as follows: Superficial Vertically Running Muscles
Intermediate Oblique Running Muscles
Deepest Muscles Interspinales Intertransversarii
Knowledge of the detailed attachments of the various muscles of the back has no practical value to a clinical professional, and the attachments are therefore omitted in this text. Splenius The splenius is a detached part of the deep muscles of the back. It consists of two parts. The splenius capitis arises from the lower part of the ligamentum nuchae and the upper four thoracic spines and is inserted into the superior nuchal line of the occipital bone and the mastoid process of the temporal bone. The splenius cervicis has a similar origin but is inserted into the transverse processes of the upper cervical vertebrae. Nerve Supply - All the deep muscles of the back are innervated by the posterior rami of the spinal nerves. Muscular Triangles of the Back Auscultatory Triangle The auscultatory triangle is the site on the back where breath sounds may be most easily heard with a stethoscope. The boundaries are the latissimus dorsi, the trapezius, and the medial border of the scapula. Lumbar Triangle The lumbar triangle can refer to either the inferior lumbar (Petit) triangle, which lies superficially, or the superior lumbar (Grynfeltt) triangle, which is deep and superior to the inferior triangle. Of the two, the superior triangle is the more consistently found in cadavers, and is more commonly the site of herniation*; however, the inferior lumbar triangle is often simply called the lumbar triangle, perhaps owing to its more superficial location and ease in demonstration. Deep Fascia of the Back (Thoracolumbar Fascia) The lumbar part of the deep fascia is situated in the interval between the iliac crest and the 12th rib. It forms a strong aponeurosis and laterally gives origin to the middle fibers of the transversus and the upper fibers of the internal oblique muscles of the abdominal wall. Medially, the lumbar part of the deep fascia splits into three lamellae. The posterior lamella covers the deep muscles of the back and is attached to the lumbar spines. The middle lamella passes medially, to be attached to the tips of the transverse processes of the lumbar vertebrae; it lies in front of the deep muscles of the back and behind the quadratus lumborum. The anterior lamella passes medially and is attached to the anterior surface of the transverse processes of the lumbar vertebrae; it lies in front of the quadratus lumborum muscle.
Arrangement of the deep muscles of the back. B. Lateral view of the skeleton showing the line of gravity. Because the greater part of the body weight lies anterior to the vertebral column, the deep muscles of the back are important in maintaining the normal postural curves of the vertebral column in the standing position.
The intrinsic back muscles The intrinsic back muscles are part of the trunk musculature. It comprises a system of deep back muscles at the vertebral column ranging from the pelvis up to the head. They are located in an osteofibrous canal, bounded by the vertebrae, the ribs and the thoracolumbar fascia. All intrinsic back muscles are innervated by the posterior branches of the spinal nerves. Embryologically they derive from the dorsal part of the myotomes (epimere) which reside locally during the entire development for which reason they are also referred to as true or autochthonous back muscles. In contrast the back muscles deriving from the ventral part of the myotomes (hypomere), e.g. latissimus dorsi muscle and trapezius muscle, migrate into the trunk musculature subsequently (secondary back muscles).
The intrinsic back musculature is subdivided into a medial and lateral tract and the deep neck muscles. Medial tract The medial tract extends between the spinal and transverse processes of the vertebrae. It is innervated by the medial branches of the posterior branches of the spinal nerves. One differentiates between the spinal and transversospinal system. The spinalis muscle and the interspinales muscles belong to the spinal system. They connect the spinal processes of neighboring vertebrae. The spinalis muscle originates slightly laterally from the interspinales muscles. The transversospinal system comprises the short and long rotatores muscles, multifidus muscle and the semispinalis muscle. They all run diagonally from the transverse to the spinal processes. The short rotatores muscles insert at the next higher vertebrae, the long rotatores muscles at the second higher vertebrae. The multifidus muscle skips 2-4 vertebrae, the semispinalis muscle even 4-7 vertebrae. Furthermore the semispinalis muscle has a robust insertion at the occipital bone.
Lateral tract The lateral tract is a system of long longitudinal muscles. It lies more superficially than the medial tract and inserts more laterally. It is innervated by the lateral branches of the posterior branches of the spinal nerves. One differentiates between the sacrospinal, intertransverse and spinotransverse system. The sacrospinal system consists of the longissimus muscle and iliocostalis muscle. Both share an origin tendon at the thoracolumbar fascia. They have numerous origins and insertions at the ribs and transverse processes. In addition the longissimus capitis muscle inserts at the mastoid process of the temporal bone. The splenius muscle builds the spinotransverse system. It originates at the spinal processes of the upper thoracic and cervical vertebrae and runs laterocranially. The intertransverse system comprises the intertransversarii muscles and levatores costarum muscles. They extend between two neighboring transverse processes. The levatores costarum muscles are innervated by both the anterior and posterior branches of the spinal nerves (double innervation). Part of the intertransversarii muscles are even innervated only by anterior branches of the spinal nerves for which reason they do not count as intrinsic back muscles.
Deep neck muscles The deep neck muscles (suboccipital muscles) are innervated by the posterior branch of the first spinal nerve (C1), the suboccipital nerve, and are therefore considered as intrinsic back muscles. They consist of four paired muscles: Rectus capitis posterior major muscle (spinal process of axis → inferior nuchal line) Rectus capitis posterior minor muscle (posterior tubercle of atlas → inferior nuchal line) Obliquus capitis superior muscle (transverse process of atlas → inferior nuchal line) Obliquus capitis inferior muscle (spinal process of axis → transverse process of atlas)
Function The intrinsic back musculature is essential for the stabilization and movement of the vertebral column. Bilateral contraction stretches the body (dorsal extension), unilateral contraction bends the body to one side (lateral flexion). The rotation is effected with the assistance of the oblique abdominal muscles. The deep neck muscles support the movement of the atlanto-occipital joint. They have particularly many muscle spindles contributing to the proprioception of the head.
The contents of the suboccipital triangle are the suboccipital nerve and the vertebral artery. Note that the suboccipital nerve (dorsal ramus of C1) emerges between the occipital bone and vertebra C1. The suboccipital nerve supplies motor innervation to the muscles of the suboccipital region. The suboccipital nerve is the only dorsal ramus that has no cutaneous distribution. Identify the vertebral artery. Use an illustration to study the course of the vertebral artery through the neck and into the skull.
* hernia - A hernia is the protrusion of an organ or the fascia of an organ through the wall of the cavity that normally contains it. There are different kinds of hernia, each requiring a specific management or treatment.