Muscles of the back • Depending on their location in relation to vertebral column muscles of back are classified in to following groups. 1. Posterior group - behind vertebral column & are subdivided into: .Superficial (Secondary) muscles of the back .Deep ( primary or posterior vertebral) muscles of back. .Intermediate - groups of muscles of the back. 2. Anterior group - these are found ventral to vertebral column & are also =anterior vertebral (prevertebral) muscles The posterior group of back muscles • The primary muscles develop from segmental myotomes while secondary muscles are derived from limb buds. • The deep primary muscles are found in groove between spinous and transverse processes. • In neck region they are covered by nucheal fascia & in thoracic & lumbar regions by thoracolumbar fascia. • All of them are innervated by dorsal rami of the spinal nerves The Superficial or Secondary muscle of the back • To the secondary muscles belong some of the muscles of the shoulder girdle like: 1. Trapezius 2. Latissimus dorsi 3. Rhomboid major and minor 4. Levator scapulae . Trapezius divided into three parts according to direction of its fibres. 1. Descending or superior part 2. Transverse or middle part 3. Ascending or inferior part . Origin External occipital protuberance Medial part of the superior nucheal line Ligamentum nuchae Spinous processes of all thoracic vertebrae . Insertion Lateral 1/3 of the clavicle (descending fibres) Acromion process of the scapula (transverse fibres) Scapular spine (ascending fibres) . Action trapezius participates in movement activities & fixation of shoulder joint. . Movement: a. Descending fibres Elevation of shoulder girdle. Increase cervical curvature by extending head & neck or by pulling occipital bone down wards. Upward rotation, retraction & elevation of scapula. b. Transverse fibres Pull the scapula in the direction of the vertebral column (retraction of the scapula). c.Ascending fibres Depression of elevated shoulder girdle. Upward rotation, retraction & depression of scapula. . Innervation - Spinal part of the accessory nerve, cervical plexus (C3 and C4) 2. Latissimus dorsi . It has four parts (inferior, vertebral, costal & iliac parts). .Origin: a. Inferior part - Inferior angle of scapula b. Vertebral part - Spinous processes of thoracic vertebrae 7 - 12, -Spinous processes of the all the lumbar vertebrae - Sacrum - Thoracolumbar fascia c. Costal part - (9th) 10th - 12th ribs by fleshy fibres d. Iliac part - iliac crest .Insertion - floor of intertubercular sulcus or groove on the humerus .Innervation - thoracodorsal (Middle scapular) nerve from posterior cord of brachial plexus. .Action – Medial rotation, adduction & retroversion (extension) of shoulder. Acts as an accessory muscle of expiration during exertion & cough. Depression of the elevated shoulder Bilateral contraction of latissimus dorsi muscle pulls the shoulder backwards. . Special note - latissimus dorsi is a large triangular muscle placed superficially except in its upper most part, where it is covered by trapezius. • Its lower part forms posterior boundary of lumbar triangle & inferior angle of triangle of auscultation. • It forms posterior axillary fold together with teres major and contributes to posterior wall of axilla. • Lumbar triangle: Boundaries - Anterior - external oblique - Floor – internal oblique - Posterior - latissimus dorsi - Inferior - iliac crest .Triangle of auscultation - upper border of latissimus dorsi is overlapped by lateral border of trapezius. • The angle thus formed is converted to a triangle by medial border of underlying scapula. This interval, floor of which is formed by rhomboid major is called triangle of auscultation. • This triangle is convenient for auscultation because it is directly related to chest wall when scapula is pulled forward and rotated around chest by the serratus anterior. Heart and lung sounds can be heard more clearly through this thin region of the thoracic wall. • Boundaries - Medial - trapezius - Lateral - medial border of scapula - Inferior - Latissimus dorsi - Floor - rhomboid major • Deep muscles of the back • lie on side of vertebral column and are involved in movement of vertebral column, head and neck. • All of them are innervated by dorsal rami of the spinal nerves. • Classification: subdivided into five groups. 1. Spinotransversal system 2. Sacrospinal system (Erector spinae) 3. Transversospinal system 4. Short segmental muscles of back (deepest layer) 5. Deep short muscles of neck (Suboccipital muscles) I. Spinotranversal system run obliquely from spinous processes to transverse processes In neck region they are nearly superficial. To this system belong: a. Splenius capitis muscle b. Splenius cervicis muscle II. Sacrospinal system (erector spinae) – run parallel to vertebral column extending from sacrum to back, neck and partly to head divided in to lateral, intermediate & medial parts, which are composed of three muscles each. . a. Iliocostalis muscle - Lateral part . 1. Iliocostalis lumborum . 2. Iliocoatalis thoracis . 3. Iliocostalis cervicis . b. Longissimus muscle (Intermediate part) 1. Longissimus thoracis 2. Longissimus cervicis 3. Longissimus capitis . c. Spinalis muscle (medial part) 1. Spinalis lumborum 2. Spinalis thoracis 3. Spinalis cervicis III. Transversospinal system extend obliquely from transverse processes to spinous processes run from sacrum to back, neck & partly to head divided in to three. . a. Semispinalis muscle (absent in the lumbar region) 1. Semispinalis thoracis 2. Semispinalis cervicis 3. Semispinalis capitis b. Multifidus Muscle c. Rotatores muscle 1. Rotatores lumborum 2. Rotatores thoracis 3. Rotatores cervicis IV. Short segmental muscles of the back - these form the deepest layer of the back muscles. a. Interspinal muscles b. Intertransverse muscles c. Levator costarum V. Deep short muscles of the neck (suboccipital muscles) found deep to the semispinalis capitis and are involved in the movement of the head. a. Rectus capitis lateralis b. Rectus capitis anterior c. Rectus capitis posterior major d. Rectus capitis posterior minor e. Obliquus capitis inferior (atlantis) f. Obliquus capitis superior Intermediate group of back muscles • These groups assist inspiration; therefore they are accessory muscles of respiration. They are constituted by two muscles. a. Serratus posterior superior b. Serratus posterior inferior Anterior vertebral muscles • These muscles are found only in the cervical and lumbar regions and are innervated by the ventral rami of the spinal nerves in the respective regions. • I. In neck region they are divided in to lateral & medial groups: a. Lateral group 1. Scalenus anterior 2. Scalenus medius 3. Scalenus posterior b. Medial group 1. Longus colli 2. Longus cervicis II. In lumbar region there are three anterior vertebral muscles. 1. Psoas major 2. Psoas minor 3. Quadratus lumborum Short muscles of the neck (Suboccipital muscles) • This group is composed of six pairs of muscles. 1. Rectus capitis posterior minor muscle 2. Rectus capitis posterior major muscle 3. Rectus capitis lateralis muscle 4. Rectus capitis anterior muscle 5. Obliquus capitis inferior muscle 6. Obliquus capitis superior muscle • Innervation - They are innervated by the suboccipital nerve, which is a dorsal branch of the first spinal nerve. • Action - If contraction occurs on one side the face will be turned to the same side but in their bilateral contraction they cause the extension of the neck Fascia of the back • Fascia of the back is attached to superior nuchal line above and to the iliac crest below. 1. Nuchal fascia - it is the continuation of the superficial fascia of the neck forming the upper part of the fascia of the back. It is attached to the superior nuchal line. 2. Thoracolumbar fascia - These is found in lumbar region and its deep layer forms lumbar aponeurosis that provides origin of transverse abdominis muscle. Nerves and blood vessels of the back • Nerves - nerve supply of back is provided by dorsal rami of the spinal nerves & meningeal branches of spinal nerves • Dorsal rami of the spinal nerves spinal nerves divide into ventral and dorsal branches (rami) dorsal rami re-branch in to medial & lateral branches medial branches give a motor innervation to muscles & lateral branches give sensory supply to skin of back. To these nerves belong the suboccipital nerve from C1, the greater occipital nerve from C2 and third occipital nerve from C3. • Meningeal branches Each spinal nerve give off a meningeal branch or a sinuvertebral nerve which re-enters vertebral canal divide in to fine filaments that are connected with those from adjacent meningeal branches They supply dura mater, posterior longitudinal ligament, periosteum, epidural & intraosseous blood vessels Meningeal branches of first three cervical nerves give off branches that ascend through foramen magnum & supply dura mater of anterior part of floor of the posterior cranial fossa • Blood vessels - vertebral column & spinal cord get their blood supply from following arteries. . In neck region - vertebral - occipital - deep cervical - ascending cervical . In thoracic and abdominal regions - Posterior intercostal - subcostal - lumbar . In pelvis - iliolumbar - lateral sacral - some other branches of internal iliac • The venous blood is drained through: anterior and posterior internal vertebral venous plexuses that drain in to the epidural venous plexus. anterior and posterior external vertebral venous plexuses.
