The Back Muscles

Upper trapezius - Origin

Occipital bone; spinous processes C1-C7.

Upper trapezius - Insertion

Lateral 1/3 of clavicle.

Upper trapezius - Innervation

Accessory nerve (CN XI); cervical plexus (C3-C4).

Upper trapezius - Action

Draws scapula obliquely upward; rotates glenoid cavity superiorly; tilts head to same side and rotates it to opposite side; steadies scapula on thorax.

Middle trapezius - Origin

Aponeurosis at T1-T4 spinous processes.

Middle trapezius - Insertion

Acromion.

Middle trapezius - Innervation

Accessory nerve (CN XI); cervical plexus (C3-C4).

Middle trapezius - Action

Draws scapula medially; steadies scapula on thorax.

Lower trapezius - Origin

Spinous processes T5-T12.

Lower trapezius - Insertion

Scapular spine.

Lower trapezius - Innervation

Accessory nerve (CN XI); cervical plexus (C3-C4).

Lower trapezius - Action

Draws scapula medially downward; steadies scapula on thorax.

Latissimus dorsi - Vertebral part - Origin

Spinous processes T7-T12; thoracolumbar fascia.

Latissimus dorsi - Vertebral part - Insertion

Crest of lesser tuberosity of humerus (anterior angle).

Latissimus dorsi - Vertebral part - Innervation

Thoracodorsal nerve (C6-C8).

Latissimus dorsi - Vertebral part - Action

Internal rotation, adduction, extension, respiration.

Latissimus dorsi - Scapular part - Origin

Inferior angle of scapula.

Latissimus dorsi - Scapular part - Insertion

Crest of lesser tuberosity of humerus (anterior angle).

Latissimus dorsi - Scapular part - Innervation

Thoracodorsal nerve (C6-C8).

Latissimus dorsi - Scapular part - Action

Internal rotation, adduction, extension, respiration.

Latissimus dorsi - Costal part - Origin

Ribs 9-12.

Latissimus dorsi - Costal part - Insertion

Crest of lesser tuberosity of humerus (anterior angle).

Latissimus dorsi - Costal part - Innervation

Thoracodorsal nerve (C6-C8).

Latissimus dorsi - Costal part - Action

Internal rotation, adduction, extension, respiration.

Latissimus dorsi - Iliac part - Origin

Posterior 1/3 of iliac crest.

Latissimus dorsi - Iliac part - Insertion

Crest of lesser tuberosity of humerus (anterior angle).

Latissimus dorsi - Iliac part - Innervation

Thoracodorsal nerve (C6-C8).

Latissimus dorsi - Iliac part - Action

Internal rotation, adduction, extension, respiration.

Teres major - Origin

Inferior angle of scapula.

Teres major - Insertion

Crest of lesser tuberosity of humerus (anterior angle).

Teres major - Innervation

Lower scapular nerve (C5-C7).

Teres major - Action

Internal rotation, adduction, extension.

Levator scapulae - Origin

Transverse processes C1-C4.

Levator scapulae - Insertion

Superior angle of scapula.

Levator scapulae - Innervation

Dorsal scapular nerve (C4-C5).

Levator scapulae - Action

Draws scapula medially upward while moving inferior angle medially; inclines neck to same side.

Rhomboid minor - Origin

Spinous processes C6-C7.

Rhomboid minor - Insertion

Medial border of scapula above scapular spine.

Rhomboid minor - Innervation

Dorsal scapular nerve (C4-C5).

Rhomboid minor - Action

Steadies scapula; draws scapula medially upward.

Rhomboid major - Origin

Spinous processes T1-T4.

Rhomboid major - Insertion

Medial border of scapula below scapular spine.

Rhomboid major - Innervation

Dorsal scapular nerve (C4-C5).

Rhomboid major - Action

Steadies scapula; draws scapula medially upward.

Serratus posterior superior - Origin

Ligamentum nuchae; spinous processes C7-T3.

Serratus posterior superior - Insertion

Superior borders of ribs 2-4.

Serratus posterior superior - Innervation

Intercostal nerves 2-5.

Serratus posterior superior - Action

Elevates ribs.

Serratus posterior inferior - Origin

Spinous processes T11-L2.

Serratus posterior inferior - Insertion

Inferior borders of ribs 8-12.

Serratus posterior inferior - Innervation

Spinal nerves T9-T12 (anterior rami).

Serratus posterior inferior - Action

Depresses ribs.

Splenius capitis - Origin

Ligamentum nuchae; spinous processes C7-T3.

Splenius capitis - Insertion

Occipital bone (lateral superior nuchal line); mastoid process.

Splenius capitis - Innervation

Spinal nerves C1-C6 (posterior rami, lateral branches).

Splenius capitis - Action

Bilateral: extends cervical spine and head. Unilateral: flexes and rotates head to same side.

Splenius cervicis - Origin

Spinous processes T3-T6.

Splenius cervicis - Insertion

Transverse processes C1-C2.

Splenius cervicis - Innervation

Spinal nerves C1-C6 (posterior rami, lateral branches).

Splenius cervicis - Action

Bilateral: extends cervical spine and head. Unilateral: flexes and rotates head to same side.

Iliocostalis cervicis - Origin

Ribs 3-7.

Iliocostalis cervicis - Insertion

Transverse processes C4-C6.

Iliocostalis cervicis - Innervation

Spinal nerves C8-L1 (posterior rami, lateral branches).

Iliocostalis cervicis - Action

Bilateral: extends spine. Unilateral: bends spine laterally to same side.

Iliocostalis thoracis - Origin

Ribs 7-12.

Iliocostalis thoracis - Insertion

Ribs 1-6.

Iliocostalis thoracis - Innervation

Spinal nerves C8-L1 (posterior rami, lateral branches).

Iliocostalis thoracis - Action

Bilateral: extends spine. Unilateral: bends spine laterally to same side.

Iliocostalis lumborum - Origin

Sacrum, iliac crest, thoracolumbar fascia.

Iliocostalis lumborum - Insertion

Ribs 6-12; thoracolumbar fascia; transverse processes of upper lumbar vertebrae.

Iliocostalis lumborum - Innervation

Spinal nerves C8-L1 (posterior rami, lateral branches).

Iliocostalis lumborum - Action

Bilateral: extends spine. Unilateral: bends spine laterally to same side.

Longissimus capitis - Origin

Transverse processes T1-T3; transverse and articular processes C4-C7.

Longissimus capitis - Insertion

Mastoid process (temporal bone).

Longissimus capitis - Innervation

Spinal nerves C1-L5 (posterior rami, lateral branches).

Longissimus capitis - Action

Bilateral: extends head. Unilateral: flexes and rotates head to same side.

Longissimus cervicis - Origin

Transverse processes T1-T6.

Longissimus cervicis - Insertion

Transverse processes C2-C5.

Longissimus cervicis - Innervation

Spinal nerves C1-L5 (posterior rami, lateral branches).

Longissimus cervicis - Action

Bilateral: extends spine. Unilateral: bends spine laterally to same side.

Longissimus thoracis - Origin

Sacrum, iliac crest, spinous processes of lumbar vertebrae, transverse processes of lower thoracic vertebrae.

Longissimus thoracis - Insertion

Ribs 2-12; costal processes of lumbar vertebrae; transverse processes of thoracic vertebrae.

Longissimus thoracis - Innervation

Spinal nerves C1-L5 (posterior rami, lateral branches).

Longissimus thoracis - Action

Bilateral: extends spine. Unilateral: bends spine laterally to same side.

Spinalis cervicis - Origin

Spinous processes C5-T2.

Spinalis cervicis - Insertion

Spinous processes C2-C5.

Spinalis cervicis - Innervation

Spinal nerves (posterior rami).

Spinalis cervicis - Action

Bilateral: extends cervical and thoracic spine. Unilateral: bends cervical and thoracic spine to same side.

Spinalis thoracis - Origin

Spinous processes (lateral surfaces) T10-L3.

Spinalis thoracis - Insertion

Spinous processes (lateral surfaces) T2-T8.

Spinalis thoracis - Innervation

Spinal nerves (posterior rami).

Spinalis thoracis - Action

Bilateral: extends cervical and thoracic spine. Unilateral: bends cervical and thoracic spine to same side.

Semispinalis capitis - Origin

Transverse and articular processes C4-T7.

Semispinalis capitis - Insertion

Occipital bone between superior and inferior nuchal lines.

Semispinalis capitis - Innervation

Spinal nerves (posterior rami).

Semispinalis capitis - Action

Bilateral: extends thoracic and cervical spines and head; stabilizes craniovertebral joints. Unilateral: bends head, cervical and thoracic spines to same side; rotates to opposite side.

Semispinalis cervicis - Origin

Transverse processes T1-T6.

Semispinalis cervicis - Insertion

Spinous processes C2-C5.

Semispinalis cervicis - Innervation

Spinal nerves (posterior rami).

Semispinalis cervicis - Action

Bilateral: extends thoracic and cervical spines and head; stabilizes craniovertebral joints. Unilateral: bends head, cervical and thoracic spines to same side; rotates to opposite side.