73 Back

Back. Regions.

Regions of the Back

• Cervical region – upper part of the back, supporting the neck

• Thoracic region – mid-back, associated with thoracic vertebrae and ribs

• Lumbar region – lower back, between thorax and pelvis

• Sacral region – over the sacrum and coccyx, posterior pelvic area

• Gluteal region – buttocks area (posterior pelvic region)

Muscles of the Back - Groups

Superficial (Extrinsic) Muscles

• Mainly involved in movements of the upper limb and shoulder

• Innervated mostly by anterior rami or cranial nerves

• Muscles:

  • Trapezius

  • Latissimus dorsi

  • Levator scapulae

  • Rhomboid major and minor

Intermediate Muscles

• Sometimes considered part of respiratory muscles

• Attach to ribs, assist in respiration

• Muscles:

  • Serratus posterior superior (elevates ribs)

  • Serratus posterior inferior (depresses ribs)

Deep (Intrinsic) Muscles

• Responsible for movement and stabilization of the vertebral column

• Innervated by posterior (dorsal) rami of spinal nerves

• Divided into 3 layers:

  • Superficial layer:

    • Splenius capitis

    • Splenius cervicis

  • Intermediate layer (erector spinae group):

    • Iliocostalis

    • Longissimus

    • Spinalis

  • Deep layer (transversospinalis group):

    • Semispinalis

    • Multifidus

    • Rotatores

Functions of Back Muscles

• Superficial group: Move the shoulder and upper limb

• Intermediate group: Aid in respiration

• Deep group: Maintain posture and move vertebral column (extension, rotation, lateral flexion)

Muscles of the Back - Superficial - Trapezius

• Origin:

  • External occipital protuberance

  • Medial third of the superior nuchal line

  • Ligamentum nuchae

  • Spinous processes of C7–T12.

• Insertion:

  • Lateral third of the clavicle, acromion, and spine of the scapula.

• Action:

  • Upper fibers: Elevate and upwardly rotate the scapula.

  • Middle fibers: Retract the scapula.

  • Lower fibers: Depress and assist in upward rotation of the scapula.

• Nerve Supply:

  • Motor: Spinal accessory nerve (CN XI).

  • Sensory: C3 and C4 spinal nerves (proprioception).

Muscles of the Back - Superficial - Latissimus Dorsi

• Origin:

  • Spinous processes of T7–T12, thoracolumbar fascia, iliac crest, and inferior 3–4 ribs.

• Insertion:

  • Floor of the intertubercular sulcus of the humerus.

• Action:

  • Extends, adducts, and medially rotates the humerus.

  • Assists in forced expiration.

• Nerve Supply:

  • Thoracodorsal nerve (C6–C8)

Muscles of the Back - Superficial - Levator Scapulae

• Origin:

  • Transverse processes of C1–C4.

• Insertion:

  • Medial border of the scapula, superior to the spine.

• Action:

  • Elevates the scapula.

  • Rotates the scapula downward.

• Nerve Supply:

  • Dorsal scapular nerve (C4, C5) and cervical nerves (C3, C4).

Muscles of the Back - Superficial - Rhomboid Major

• Origin: Spinous processes of T2–T5.

• Insertion: Medial border of the scapula from the spine to the inferior angle.

• Action:

  • Retracts the scapula.

  • Rotates the scapula downward.

  • Stabilizes the scapula.

• Nerve Supply:

  • Dorsal scapular nerve (C4, C5).

Muscles of the Back - Superficial - Rhomboid Minor

• Origin: Spinous processes of C7–T1 and ligamentum nuchae.

• Insertion: Medial border of the scapula near the spine.

• Action:

  • Retracts the scapula.

  • Rotates the scapula downward.

  • Stabilizes the scapula.

• Nerve Supply:

  • Dorsal scapular nerve (C4, C5).

Muscles of the Back - Intermediate - Serratus Posterior Superior

• Origin:

  • Ligamentum nuchae, spinous processes of C7–T3.

• Insertion:

  • Upper borders of ribs 2–5.

• Action:

  • Elevates the ribs during inspiration.

• Nerve Supply:

  • Intercostal nerves (T2–T5).

Muscles of the Back - Intermediate - Serratus Posterior Inferior

• Origin:

  • Spinous processes of T11–L2 and thoracolumbar fascia.

• Insertion:

  • Inferior borders of ribs 9–12.

• Action:

  • Depresses the ribs during expiration.

• Nerve Supply:

  • Intercostal nerves (T9–T12).

Muscles of the Back - Deep Superficial Layer - Splenius Capitis

• Origin: Spinous processes of C7–T3.

• Insertion: Mastoid process and superior nuchal line.

• Action: Extends and rotates the head.

• Nerve Supply: Posterior rami of middle cervical nerves

Muscles of the Back - Deep Superficial Layer - Splenius Cervicis

• Origin: Spinous processes of T3–T6.

• Insertion: Transverse processes of C1–C3.

• Action: Extends and rotates the neck.

• Nerve Supply: Posterior rami of lower cervical nerves.

Muscles of the Back - Deep Intermediate Layer (Erector Spinae Group) - Iliocostalis (lateral column), Longissimus (intermediate column), Spinalis (medial column)

• Origin: Broad tendon from the iliac crest, sacrum, and lumbar spinous processes.

• Insertion:

  • Iliocostalis: Angles of lower ribs and cervical transverse processes.

  • Longissimus: Ribs, transverse processes, and mastoid process.

  • Spinalis: Spinous processes.

• Action:

  • Unilateral: Lateral flexion of the vertebral column.

  • Bilateral: Extension of the vertebral column and head.

• Nerve Supply:

  • Posterior rami of spinal nerves.

Muscles of the Back - Deep Layer (Transversospinalis Group) - Semispinalis

• Origin: Transverse processes of C4–T12.

• Insertion: Occipital bone and spinous processes (spanning 4–6 segments).

• Action: Extends and rotates the vertebral column and head.

• Nerve Supply: Posterior rami of spinal nerves.

Muscles of the Back - Deep Layer (Transversospinalis Group) - Multifidus

• Origin: Sacrum, iliac crest, transverse processes.

• Insertion: Spinous processes (spanning 2–4 segments).

• Action: Stabilizes the vertebrae during movement.

• Nerve Supply: Posterior rami of spinal nerves.

Muscles of the Back - Deep Layer (Transversospinalis Group) - Rotatores

• Origin: Transverse processes.

• Insertion: Spinous processes (spanning 1–2 segments).

• Action: Stabilizes vertebrae and assists in rotation.

• Nerve Supply: Posterior rami of spinal nerves.

Muscles of the Back - Minor Deep Layer - Interspinales

• Origin:

  • Spinous processes of cervical, thoracic, and lumbar vertebrae.

• Insertion:

  • Spinous process of the vertebra immediately above.

• Action:

  • Aids in extension of the vertebral column by stabilizing adjacent vertebrae during movement.

  • Contributes to segmental stability of the spine.

• Nerve Supply:

  • Posterior rami of spinal nerves.

Muscles of the Back - Minor Deep Layer - Intertransversarii

• Origin:

  • Transverse processes of cervical, thoracic, and lumbar vertebrae.

• Insertion:

  • Transverse process of the vertebra immediately above.

• Action:

  • Aids in lateral flexion of the vertebral column.

  • Acts as a stabilizer for the vertebrae during movement of the trunk.

• Nerve Supply:

  • Cervical region: Anterior and posterior rami of cervical spinal nerves.

  • Thoracic and lumbar regions: Posterior rami of spinal nerves.

Muscles of the Back - Minor Deep Layer - Levatores Costarum

• Origin:

  • Tips of the transverse processes of C7–T11 vertebrae.

• Insertion:

  • Outer surface of the rib immediately below (or two ribs below for longer fibers).

• Action:

  • Elevates the ribs during respiration, assisting in deep inspiration.

  • Aids in lateral flexion of the thoracic spine.

• Nerve Supply:

  • Posterior rami of C8–T11 spinal nerves.