Superficial vs Deep Back Muscles Anatomy

Study Notes

Superficial back muscles primarily connect the trunk to the upper limb (scapula and humerus), supporting and moving the upper limb. Innervation is via ventral rami of spinal nerves, which usually innervate upper limb muscles.
Deep back muscles, also known as paraspinal muscles, are located along the spinous processes. They support and move the vertebral column and are innervated by dorsal rami of spinal nerves, which innervate intrinsic back muscles.

Origin: External occipital protuberance, nuchal ligament, spinous processes of C7-T12 vertebrae.
Insertion: Lateral 1/3 of clavicle, acromion process, spine of scapula.
Actions:
- Elevation (upper fibers): Pulls the scapula upwards (shrugging).
- Adduction (middle fibers): Pulls the scapula towards the midline.
- Depression (lower fibers): Pulls the scapula downwards.
- Rotation (all fibers): Combined contraction results in upward rotation of the scapula, part of scapulothoracic rhythm.
Innervation: Spinal accessory nerve (cranial nerve XI). This nerve originates segmentally from the cervical spinal cord, passing through the foramen magnum and jugular foramen; it innervates the trapezius and sternocleidomastoid muscles.

Origin: Transverse processes of C1-C4 vertebrae.
Insertion: Superior angle of scapula.
Action: Elevates the scapula.
Innervation: Dorsal scapular nerve (originating from C5 spinal cord level). This nerve travels through the brachial plexus to innervate the levator scapulae, rhomboid minor, and rhomboid major muscles.

Rhomboid Minor:
- Origin: Spinous processes of C7 and T1 vertebrae.
- Insertion: Medial border of scapula, at the level of the spine.
Rhomboid Major:
- Origin: Spinous processes of T2 to T5 vertebrae.
- Insertion: Medial border of scapula, below the spine.
Action (Combined): Adduct the scapula, pulling it towards the midline.
Innervation: Dorsal scapular nerve (originating from C5 spinal cord level). This nerve passes through the brachial plexus to reach the levator scapulae, rhomboid minor, and rhomboid major.

Origin: T7 to sacral region of vertebral column, thoracolumbar fascia.
Insertion: Intertubercular groove of the humerus.
Actions:
- Adduction: Pulls the humerus toward the body's midline.
- Extension: Moves the humerus from a flexed to an extended position.
Innervation: Thoracodorsal nerve (originating from C6, C7, and C8 spinal cord levels). This nerve travels through the brachial plexus to reach the latissimus dorsi muscle.