Back Muscles

Trapezius

• Origin: External occipital protuberance, nuchal ligament, spinous processes of C7–T12

• Insertion: Lateral 1/3 of clavicle, acromion, spine of scapula

• Action: Elevates, retracts, depresses scapula; rotates glenoid cavity upward

• Nerve: Spinal accessory nerve (CN XI); C3–C4 for proprioception

• Blood Supply: Transverse cervical artery

Latissimus Dorsi

• Origin: Spinous processes of T7–L5, thoracolumbar fascia, iliac crest, inferior 3–4 ribs

• Insertion: Intertubercular sulcus of humerus

• Action: Extends, adducts, and medially rotates humerus

• Nerve: Thoracodorsal nerve (C6–C8)

• Blood Supply: Thoracodorsal artery

Rhomboid Major

• Origin: Spinous processes of T2–T5

• Insertion: Medial border of scapula (below spine to inferior angle)

• Action: Retracts and rotates scapula; stabilizes scapula against thoracic wall

• Nerve: Dorsal scapular nerve (C4–C5)

• Blood Supply: Dorsal scapular artery

Rhomboid Minor

• Origin: Nuchal ligament, spinous processes of C7–T1

• Insertion: Medial border of scapula at level of spine

• Action: Retracts and rotates scapula

• Nerve: Dorsal scapular nerve (C4–C5)

• Blood Supply: Dorsal scapular artery

Levator Scapulae

• Origin: Transverse processes of C1–C4

• Insertion: Superior angle of scapula, medial border above spine

• Action: Elevates scapula, tilts glenoid cavity downward

• Nerve: Dorsal scapular nerve (C5) and cervical nerves (C3–C4)

• Blood Supply: Dorsal scapular artery

Serratus Posterior Superior

• Origin: Nuchal ligament, spinous processes of C7–T3

• Insertion: Superior borders of ribs 2–5

• Action: Elevates ribs during inspiration

• Nerve: Intercostal nerves (T2–T5)

• Blood Supply: Posterior intercostal arteries

Serratus Posterior Inferior

• Origin: Spinous processes of T11–L2

• Insertion: Inferior borders of ribs 9–12

• Action: Depresses ribs during forced expiration

• Nerve: Intercostal nerves (T9–T12)

• Blood Supply: Posterior intercostal arteries

Splenius Captis

• Origin: Nuchal ligament, spinous processes of C7–T3/T4

• Insertion: Mastoid process, lateral part of superior nuchal line

• Action: Extends head (bilateral), rotates head to same side (unilateral)

• Nerve: Posterior rami of cervical spinal nerves

• Blood Supply: Occipital artery, deep cervical artery

Splenius Cervicis

• Origin: Spinous processes of T3–T6

• Insertion: Transverse processes of C1–C3/C4

• Action: Extends neck (bilateral), rotates neck to same side (unilateral)

• Nerve: Posterior rami of cervical spinal nerves

• Blood Supply: Occipital artery, deep cervical artery

Iliocostalis

• Origin: Iliac crest, sacrum, lumbar spinous processes

• Insertion: Angles of ribs, cervical transverse processes

• Action: Extends and laterally flexes vertebral column

• Nerve: Posterior rami of spinal nerves

• Blood Supply: Dorsal branches of posterior intercostal, lumbar, and sacral arteries

Longissimus

• Origin: Iliac crest, sacrum, lumbar spinous processes

• Insertion: Transverse processes of thoracic and cervical vertebrae, mastoid process

• Action: Extends and laterally flexes vertebral column and head

• Nerve: Posterior rami of spinal nerves

• Blood Supply: Dorsal branches of posterior intercostal, lumbar, and sacral arteries

Spinalis

• Origin: Spinous processes of upper lumbar and lower thoracic vertebrae

• Insertion: Spinous processes of upper thoracic vertebrae and cervical vertebrae (except atlas)

• Action: Extends vertebral column

• Nerve: Posterior rami of spinal nerves

• Blood Supply: Dorsal branches of posterior intercostal, lumbar, and sacral arteries

Semispinalis

• Origin: Transverse processes of C4–T12

• Insertion: Occipital bone, spinous processes of cervical and thoracic vertebrae (4–6 segments above origin)

• Action: Extends head, neck, and thoracic spine; rotates them contralaterally

• Nerve: Posterior rami of spinal nerves

• Blood Supply: Deep cervical artery, posterior intercostal arteries