Back and Shoulder Muscles

• The shoulder girdle, also known as the pectoral girdle, includes the scapula and clavicle
• The flat, triangular scapula has 3 angles (lateral, superior, and inferior), 3 borders (superior, medial, and inferior), and 3 processes (acromion, spine, and coracoid)
• The vertebral column consists of 33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal

Superficial Muscles

• Trapezius
• Latissimus dorsi
• Levator scapulae
• Rhomboid major
• Rhomboid minor

Intermediate Muscles

• Serratus posterior superior
• Serratus posterior inferior

Deep Muscles

• Spinotransversales muscles
• Erector spinae muscles
• Transversospinales muscles
• Segmental muscles
• Suboccipital muscles

Intrinsic vs Extrinsic Muscles

• Intrinsic muscles develop in the back
• Extrinsic muscles originate embryonically from locations other than the back

Upper Humerus Bony Landmarks

• Greater tubercle: attachment site for supraspinatus, infraspinatus, and teres minor
• Lesser tubercle: attachment site for subscapularis

Trapezius

• Originates from the superior nuchal line, external occipital protuberance, ligamentum nuchae, and spinous processes CVII to TXII
• Rotates the scapula during humerus abduction
• Innervated by the motor accessory nerve and proprioception at C3 and C4

Latissimus Dorsi

• Originates from spinous processes of TVII to LV, sacrum, iliac crest, and ribs X to XII
• Extends, adducts, and medially rotates the humerus
• Innervated by the thoracodorsal nerve (C6 to C8)

Levator Scapulae

• Originates from the transverse processes of C1 to CIV
• Elevates the scapula
• Innervated by C3-C4 and the dorsal scapular nerve (C4, C5)

Rhomboid Major

• Originates from the spinous processes of TII to TV
• Retracts and elevates the scapula
• Innervated by the dorsal scapular nerve (C4, C5)

Rhomboid Minor

• Originates from the lower portion of ligamentum nuchae and spinous processes of CVII and TI
• Retracts and elevates the scapula
• Innervated by the dorsal scapular nerve (C4, C5)

Serratus Posterior Superior

• Originates from the lower portion of ligamentum nuchae, CVII-TIII spinous processes, and supraspinous ligaments
• Elevates ribs II-V
• Innervated by the anterior rami of upper thoracic nerves (TII-TV)

Serratus Posterior Inferior

• Originates from the spinous processes of TXI-LIII and supraspinous ligaments
• Depresses the ribs and prevents lower ribs from being elevated when the diaphragm contracts
• Innervated by the anterior rami of lower thoracic nerves (T9-T12)

Spinotransversales Muscles

• Originate from the lower half of the ligamentum nuchae and spinous processes CVII-TIV (Splenius Capitis) and the spinous processes of TIII-TVI (Splenius Cervicis)
• Splenius capitis draws the head back, extends the neck, and rotates the head to one side
• Splenius cervicis extends the neck and rotates the head to one side
• Innervated by the posterior rami middle and lower cervical nerves

Erector Spinae Muscles

• Originate from sacrum, spinous processes of lumbar and lower 2 thoracic vertebrae and their supraspinous ligaments and the iliac crest (Iliocostalis lumborum)
• Also originate from angles of the lower 6 ribs (Iliocostalis thoracis), angles of ribs 3-6 (Iliocostalis cervicis)
• Originate from iliocostalis in lumbar region and attached to transverse processes of lumbar vertebrae (longissimus thoracis), transverse process of upper 4 or 5 thoracic vertebrae (longissimus cervicis), transverse processes of upper 4 or 5 thoracic vertebrae and articular processes of lower 3 or 4 cervical vertebrae ( longissimus capitis), spinous processes of T10 or L2 (spinalis thoracis), lower part of ligamentum nuchae and spinous process of C8 sometime T1 to T2 ( spinalis cervicis) and usually blends with semispinalis capitis (Spinalis capitis)
• Primary extensors of the vertebral column, straighten the back, pull the head up posteriorly, vertebral column flexion, and turn the head

Transversospinales Muscles

• Originate from the transverse processes of upper 5 or 6 thoracic vertebrae ( semispinalis thoracis), transverse processes of T1 to and C8 and articular processes of C4 to C6 (semispinalis capitis) and sacrum, origin of the erector spinae, posterior superior iliac spine, mammillary processes of lumbar vertebrae, transverse processes of lumbar vertebrae, mammillary processes of lumbar vertebrae (Rotatores lumbordum) transverse processes of thoracic vertebrae (Rotatores thoracis) and articular processes of cervical vertebrae (Rotatores cervicis)
• Rotate the head at atlanto-occipital and atlanto-axial joints
• Innervated by the posterior ramus of the first cervical nerve

Segmental Muscles

• Originate in short paired muscles from transverse processes of CVII-TXI, short paired muscles attached to the spinous processes of contiguous vertebrae, and small muscles between the transverse processes of contiguous vertebrae
• Elevate ribs and act as postural muscles

Suboccipital Muscles

• Originate at the spinous process of axis (rectus capitis posterior major), posterior tubercle of atlas (rectus capitis posterior minor), transverse process of atlas (obliquus capitis superior), and spinous process of axis (obliquus capitis inferior)
• Extend the head, rotate the face to the same side as the muscle, and bend the head to the same side
• Innervated by the posterior ramus of C1

Cutaneous Innervation of the Back / Dermatomes

• C5: clavicles
• C5-C7: lateral parts of the upper limbs
• C8, T1: medial sides of the upper limbs
• C6: thumb
• C6-C8: hand
• C8: ring and little fingers
• T4: level of the nipples
• T10: umbilicus
• T12: inguinal/ groin area
• L1-L4: anterior and inner surface of lower limbs
• L4, L5, S1: foot
• S1, S2, L5: posterior outer surface of lower limbs

Lymphatic Drainage of the Back

• Superficial lymphatic drainage above the umbilicus passes superiorly to the axillary nodes
• Superficial lymphatic drainage below the umbilicus passes inferiorly to the superficial inguinal nodes
• Deep lymphatic drainage follows deep arteries to the parasternal nodes along the internal thoracic artery, lumbar nodes along the abdominal aorta, and external iliac nodes along the external iliac artery

Arterial Supply to the Muscles of the Back

• Superficial branch of the transverse cervical artery
• Acromial branch of the suprascapular artery
• Dorsal branches of posterior intercostal arteries
• Thoracodorsal artery
• Intercostal arteries