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Anatomy Chapter 10C: Posterior Trunk Muscles


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Latissimus Dorsi
Broad, flat, triangular muscle of the lower back

O: indirect attachment via lumbodorsal fascia into spines of lower six thoracic vertebrae, lumbar vertebrae, lower 3-4 ribs, and iliac crest

I: spirals around teres major to insert in floor of intertubercular groove of humerus

A: prime mover in arm (upper arm) extension
Most superficial muscle of posterior thorax, flat and triangular in shape

O: occipital bone, ligamentum nuchae, and spines of C7/all thoracic vertebrae

I: a continuous insertion along acromion and spine of scapula and lateral third of clavicle

A: Stabilizes, raises, retracts, and rotates scapula
Two rectangular muscles lying deep to trapezius and inferior to levator scapulae.

O: spinous processes of C7 and T1 and spinous processes of T2-T5

I: medial border of scapula

A; retract scapula, squaring shoulders
Levator Scapulae
Located at back and side of neck, deep to trapezius.

O: transverse processes of C1-C4

I: medial border of the scapula, superior to the spine

A: elevates/adducts scapula in concert with superior fibres of trapezius
Forms part of posterior wall of axilla. A rotator cuff muscle.

O: subscapular fossa of scapula

I: lesser tubercle of humerus

A: chief medial rotator of humerus (pec major synergist)
Located on posterior aspect of scapula, deep to trapezius. Rotator cuff muscle.

O: supraspinous fossa of scapula

I: superior part of greater tubercle of humerus

A: stabilizes shoulder joint (preventing downward dislocation)
Scapular muscle partially covered by deltoid and trapezius. Rotator cuff muscle.

O: supraspinous fossa of scapula

I: greater tubercle of humerus posterior to insertion of supraspinatus

A: Helps to hold head of humerus in glenoid cavity.
Teres Major
Thick, rounded muscle located inferior to teres minor.

O: posterior surface of scapula at inferior angle.

I: intertubercular groove of the humerus

A: posteromedially extends, medially rotates, and adducts humerus (synergist of latissimus dorsi)
Teres Minor
Small, elongated muscle inferior to infraspinatus. Rotator cuff muscle.

O: Lateral border of dorsal scapular surface

I: greater tubercle of humerus inferior to infraspinatus insertion

A: helps to hold head of humerus in glenoid cavity (infraspinatus synergist)
Small, cylindrical muscle.

O: coracoid process of scapula

I: medial surface of humerus shaft

A: Flexion and adduction of humerus. (Synergist of pec major)
Erector Spinae
Intermediate layer of intrinsic back muscles

O: ribs, transverse processes/spines of vertebrae

I: ribs, transverse processes/spines of vertebrae

A: Prime mover of back extension, lateral bending of back, maintaining posture
Quadratus Lumbornum
Fleshy muscle forming part of posterior abdominal wall.

O: iliac crest and lumbar fascia

I: transverse processes of upper lumbar vertebrae and lower margin of rib 12

A: flexes vertebral column laterally
Composite muscle forming part of deep layer of intrinsic back muscles.

O: transverse processes of C7-T12

I: occipital bone and spinous processes of cervical vertebrae/T1-T4.

A: Extends vertebral column and head and rotates them to opposite sides. (Sternocleidomastoid synergist)
Rotator Cuff
Supraspinatus, infraspinatus, subscapularis, teres minor

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