Muscles of the Back

Muscles described by their action/function (A), origin(O), insertion(I), and innervation(N)

Trapezius

• A: Steadies scapula & controls it during arm movement

• I: inserts on scapular spine, acromion, and lateral 1/3 clavicle

• O: extends from the occipital protuberance, nuchal lines/ligaments, and vertebrae C1-T12 (spinous processes and supraspinous ligaments)

• iN: Motor - spinal accessory nerve (CN XI), sensory - spinal nerves (C3, C4)

(Superficial Muscles)

Latissimus Dorsi

• A: “tacks down” inferior angle of scapula; acts on humerus in adduction, extension, and medial rotation

• I: Inserts on intertubercular (Bicipital, intertuberous) groove

• O: extends from the spinous processes of T7-T12, lumbosacral fascia, iliac breast, and ribs 9/10-12

• iN: Thoracodorsal Nerve (C6,7,8)

(Superficial Muscles)

Levator Scapulae

• A: (synergist muscle) Elevates and rotates scapula, lateral flexion of neck

• I: Inserts on medial scapular border between superior angle and level of scapular spine

• O: almost vertical fibers from C1-C4

• iN: Dorsal Scapular Nerve (C5)

(Superficial Muscles)

Rhomboid Minor

• A:Retracts scapula

• I: Insert on medial scapular border

• O: Spinous processes C7-T1

• iN: Dorsal Scapular Nerve (C5)

(Superficial Muscles)

Rhomboid Major

• A: Retracts scapula

• I: Insert on medial scapular border

• O: Spinous processes T2-T5

• iN: Dorsal Scapular Nerve (C5)

(Superficial Muscles)

Splenius Capitis

• A: bilaterally extends the head and neck; unilaterally bends and rotates the head

• I: Mastoid process of temporal bone and occipital bone

• O: Nuchal Ligament, spinous processes of C7-T4 vertebrae

• iN: Segmentally innervated by dorsal rami

Splenius Cervicis

• A: bilaterally extends the head and neck; unilaterally bends and rotates the head

• I: Transverse processes of C1-C3

• O: Spinous processes of T3-T6

• iN: Segmentally innervated by dorsal rami

Iliocostalis

• A: bilaterally, extends the vertebral column; unilaterally, lateral flexes the vertebral column

• I: Thoracolumbar fascia, ribs, cervical vertebrae

• O: Iliac crest, sacrum, ribs

• iN: segmentally innervated by dorsal rami

(Erector spinae)

Longissimus

• A: bilaterally, extends the vertebral column; unilaterally, lateral flexes the vertebral column

• I: Vertebrae and mastoid process of temporal bone

• O: Thoracodorsal fascia, transverse and cervical vertebrae

• iN: segmentally innervated by dorsal rami

(Erector spinae)

Spinalis

• A: bilaterally, extends the vertebral column; unilaterally, lateral flexes the vertebral column

• I: Spinous processes of vertebrae

• O: Spinous processes of vertebrae

• iN: segmentally innervated by dorsal rami

(Erector spinae)

Semispinalis

• A: bilaterally, extends the vertebral column; unilaterally, rotates the vertebral column contralaterally

• I: Spinous processes of thoracic and cervical vertebrae and occipital bone

• O: Transverse processes of thoracic vertebrae

• iN: segmentally innervated by dorsal rami

(Transversospinalis)

Multifidis

• A: bilaterally, extends the vertebral column; unilaterally, rotates the vertebral column contralaterally

• I: Spinous processes of lumbar, thoracic, and lower cervical vertebrae

• O: Sacrum and transverse processes of lumbar, thoracic, and cervical vertebrae

• iN: segmentally innervated by dorsal rami

(Transversospinalis)

Rotatores

• A: bilaterally, extends the vertebral column; unilaterally, rotates the vertebral column contralaterally

• I: Lamina immediately above the vertebra of origin

• O: Transverse processes of C2 vertebra to the sacrum

• iN: segmentally innervated by dorsal rami

(Transversospinalis)

Deltoid

• A: 3 Heads

  • Anterior - flex and medially rotate humerus

  • Posterior - extend and laterally rotate humerus

  • Superior - powerful abductor (after 1st 15 degrees)

• I: Deltoid tuberosity of humerus

• O: Clavicle, acromion, and spine of scapula

• iN: Axillary N (C5,6)

Supraspinatus

• A: Initiates abduction (approx. 1st 15 degrees); stabilizes head of humerus in glenoid fossa

• I: Highest facet of greater tubercle of humerus

  • Tendon passes in subacromial space; impingement

• O: Supraspinous fossa

• iN: Suprascapular Nerve (C5,6)

(Rotator Cuff Muscles)

Infraspinatus

• A: Lateral rotator of humerus; stabilizes head of humerus in glenoid fossa

• I: Middle facet of the greater tubercle of the humerus

• O: Infraspinous Fossa

• iN: Suprascapular Nerve (C5,6)

(Rotator Cuff Muscles)

Teres Minor

• A: Lateral rotator of humerus; stabilizes head of humerus in glenoid fossa

• I: Lowest facet of greater tubercle of humerus

• O: Dorsal surface of scapula adjoining lateral border

• iN: Axillary Nerve (C5,6)

(Rotator Cuff Muscles)

Subscapularis

• A: Medial rotator of humerus; stabilizes head of humerus in glenoid fossa

• I: Lesser tubercle of humerus

• O: Costal surface of scapula (subscapular fossa)

• iN: Subscapular nerve (C5,6,7)

(Rotator Cuff Muscles)

Teres Major

• A: Extends humerus, medial rotator of humerus (Adduction)

• I: Medial lip of interbercular (bicipital) groove

• O: Dorsal surface of inferior angle of scapula

• iN: Lower subscapular nerve (C5,6,7)

Also known as Latissimus Dorsi’s little helper.

(Intertubercular groove muscles)

Pectoralis Major

• A: Adduction, medial rotation, and flexion of humerus

• I: Intertubercular groove of humerus

• O: Clavicle, sternum, and costal cartilage

• iN: Medial and lateral pectoral nerves (C5-T1)

(Intertubercular groove muscles)

Serratus Anterior

• A: Most important to stabilize scapula

  • Scapular protraction, holds medial/inferior angle to thoracic wall

• I: Medial border of scapula

  • runs underneath anterior side of scapula to hook to medial border

• O: Serrated fleshy origins from ribs 1-8 (9,10)

• iN: Long thoracic nerve (C5,6,7)