Anatomy of the Back Muscles

Back Muscles

Overview

The back muscles are organized into three layers: superficial, intermediate, and deep. These layers can also be described as "extrinsic" and "intrinsic." The muscles are involved in limb movements, respiration, and acting on the vertebral column. They provide support, movement, and protection for the spinal cord and vital organs.

Muscle Layers

The back muscles can be categorized into superficial, intermediate, and deep layers based on their location and function.

Superficial Layer

The superficial layer primarily involves muscles associated with limb movement and respiration. These muscles often connect the axial skeleton to the appendicular skeleton.

  • Trapezius

  • Latissimus dorsi

  • Thoracolumbar fascia

  • Gluteus medius fascia

  • Splenius capitis

  • Splenius cervicis

  • Erector spinae

  • Serratus posterior

  • External oblique abdominis

  • Internal oblique abdominis

  • Gluteus maximus

Intermediate Layer

The intermediate layer contains muscles primarily involved in respiration and movement of the vertebral column.

  • Serratus posterior superior

  • Serratus posterior inferior

  • Erector Spinae

Deep Layer

The deep layer consists of muscles that primarily act on the vertebral column, providing stability, rotation, and extension.

  • Longissimus capitis

  • Longissimus cervicis

  • Iliocostalis

  • Semispinalis capitis

  • Spinalis cervicis

  • Iliocostalis thoracis

  • Spinalis thoracis

  • Interspinalis cervicis muscle

  • Rotatores thoracis (longus)

  • Longissimus thoracis

  • Rotatores thoracis (brevis)

  • Iliocostalis lumborum

  • Interspinalis lumborum

  • Quadratus lumborum

  • Lateral intertransversi muscle

Superficial Layer Anatomy

The superficial layer includes key anatomical landmarks and muscles that are easily palpated and visualized.

  • Superior nuchal line

  • Spinous process of axis

  • Sternocleidomastoid m.

  • Posterior triangle of neck

  • Trapezius m.

  • Spine of scapula

  • Deltoid m.

  • Semispinalis capitis m.

  • Splenius capitis m.

  • Spinous process of C7 vertebra

  • Splenius colli m.

  • Levator scapulae

  • Rhomboid minor m. (cut)

  • Supraspinatus m.

  • Infraspinatus fascia

  • Teres minor m.

  • Teres major m.

  • Latissimus dorsi m.

  • Serratus posterior superior m.

  • Rhomboid major m. (cut)

  • Infraspinatus fascia (over infraspinatus m.)

  • Teres minor m.

  • Teres major m.

  • Spinous process of T12 vertebra

  • Thoracolumbar fascia (posterior layer)

  • External abdominal oblique m.

  • Internal abdominal oblique m. in lumbar triangle (of Petit)

  • Iliac crest

  • Gluteus maximus m.

  • Latissimus dorsi m. (cut)

  • Serratus anterior m.

  • Serratus posterior inferior m.

  • 12th rib

  • Erector spinae

  • External abdominal oblique m.

  • Internal abdominal oblique m.

Intermediate Layer Anatomy

The intermediate layer consists of muscles that are situated between the superficial and deep layers, contributing to respiration and spinal movement.

  • Superior nuchal line

  • Posterior tubercle of atlas

  • Longissimus capitis m.

  • Semispinalis capitis m.

  • Splenius capitis m.

  • Splenius colli m.

  • Serratus posterior superior m.

  • Iliocostalis mm.

  • Erector spinae

  • Longissimus mm.

  • Spinalis mm.

  • Serratus posterior inferior m.

  • Tendon of origin of transversus abdominis m.

  • Rectus posterior minor capitis m.

  • Obliquus superior capitis m.

  • Rectus posterior major capitis m.

  • Obliquus inferior capitis m.

  • Longissimus capitis m.

  • Semispinalis capitis m. (cut)

  • Spinalis colli m.

  • Spinous process of C7 vertebra

  • Longissimus colli m.

  • Iliocostalis colli m.

  • Iliocostalis thoracis m.

  • Hook

  • Spinalis thoracis m.

  • Longissimus thoracis m.

  • Iliocostalis lumborum m.

  • Spinous process of T12 vertebra

  • Internal abdominal oblique m.

  • External abdominal oblique m. (cut)

  • Iliac crest

  • Transversus abdominis m.

  • Thoracolumbar fascia (posterior layer) (cut)

Deep Layer Anatomy

The deep layer contains intrinsic back muscles that primarily act on the vertebral column, providing stability and control of movement.

  • Longissimus capitis muscle

  • Longissimus cervicis muscle

  • Iliocostalis

  • Semispinal capitis muscle

  • Spinalis cervicis muscle

  • Iliocostalis cervicis

  • Iliocostalis thoracis muscle

  • Spinalis thoracis

  • Interspinalis cervicis muscle

  • Rotatores thoracis (longus)

  • Longissimus thoracis

  • Rotatores thoracis (brevis)

  • Iliocostalis lumborum muscle

  • Interspinalis lumborum

  • Quadratus lumborum muscle

  • Lateral intertransversi muscle

Specific Muscles
Superficial Layer of Deep Back Muscles

Splenius Capitis

  • Action: Head/Neck: extension (bilateral), rotation (unilateral). Key in maintaining posture and head movements.

  • Origin:- C7-T4 spinous processes

    • Ligamentum nuchae

  • Insertion:- Mastoid process

    • Superior nuchal line

  • Innervation: posterior rami. Dorsal rami of spinal nerves.

Splenius Cervicis

  • Origin: T3-6 spinous processes. These spinal processes provide a stable base for muscle contraction.

  • Insertion: C1-3 transverse processes. Allows for rotation and lateral flexion of the neck.

Intermediate Layer of Deep Back Muscles: Erector Spinae

Iliocostalis

  • Action: Spine: extension (bilateral), lateral flexion (unilateral). Critical for maintaining upright posture and controlling lateral movements.

  • Origin: *Common Origin: Sacrum, iliac crest, and thoracolumbar fascia

  • Insertion:- Cervicis: cervical transverse processes

    • Thoracis: upper ribs

    • Lumborum: lower ribs

  • Innervation: posterior rami. Innervated by dorsal rami of spinal nerves.

Longissimus

  • Origin: *Common Origin: Sacrum, iliac crest, and transverse processes of lumbar vertebrae

  • Insertion:- Capitis: mastoid process. Aids in head extension and rotation.

    • Cervicis: C2-6 transverse processes. Supports neck extension and stability.

    • Thoracis: lower ribs, thoracic transverse processes. Maintains thoracic extension and posture.

Spinalis

  • Origin: Lower thoracic spinous processes. Provides a stable anchor point for spinalis contraction.

  • Insertion: Upper thoracic spinous processes. Assists in extending the thoracic spine.

Deep Layer of Deep Back Muscles: Transversospinalis

Semispinalis

  • Action: Spine: stabilization, extension, rotation. Important for segmental control and stability.

  • Origin:- Capitis: lower cervical transverse processes

    • Cervicis & Thoracis: transverse processes

  • Insertion:- Capitis: between superior and inferior nuchal lines

    • Cervicis & Thoracis: spinous processes 4-6 segments above origin

  • Innervation: posterior rami. Dorsal rami of spinal nerves.

Multifidus

  • Origin: Transverse processes. Arises from the transverse processes of vertebrae.

  • Insertion: Spinous processes. Inserts onto the spinous processes, spanning 2-4 vertebral segments.