Lab2 - Module 2 - Anatomy of the Scapular Region: Page 1 of 7

READINGS:

Gray's Anatomy for Students (Fourth Edition): Pages: 690-710

Four muscles join the scapula to the humerus (scapulohumeral muscles): supraspinatus, infraspinatus, teres minor, and subscapularis are referred to as the rotator cuff muscles of the glenohumeral joint.

Begin with the right Scapula and Humerus.

Add the Supraspinatus muscle.

Origin - in the supraspinus fossa of the scapula (superior to the spine of the scapula).

Insertion - on the upper most portion of the greater tuberosity of the humerus.

Innervation - by the suprascapular nerve (NR C5, C6).

Action - to pull the head of the humerus tightly into the glenoid cavity initiating the first 10-15° of abduction. This provides the deltoid with an optimum angle of pull to finish abduction. It also helps in external rotation of the arm. If the deltoid muscle is paralyzed, the supraspinatus muscle can still partially abduct the humerus.

Blood supply - from the suprascapular artery.

Rotate the cadaver to visulaize this muscle.

Add the Subscapularis muscle. A large fan shaped muscle that fills the lower half of the back.

Origin - the subscapular fossa on the anterior surface of the scapula.

Insertion - on the lesser tuberosity of the humerus.

Innervation - by the upper and lower subscapular nerves (NRs C5, C6, C7).

Action - internal rotation of the arm.

Blood supply - from the subscapular artery.

Rotate the cadaver to visulaize this muscle.

Add the Infraspinatus muscle.

Origin - in the infraspinous fossa (inferior to the spine of the scapula).

Insertion - on the middle portion of the greater tuberosity of the humerus just below the supraspinatus.

Innervation - by the suprascapular nerve (NR C5, C6).

Action - is external rotation. It also acts eccentrically during the throwing motion to try and decelerate the rotation of the humerus.

Blood supply - from the suprascapular artery.

Rotate the cadaver to visulaize this muscle.

Add the Teres minor muscle.

Origin - on the upper 2/3 of the lateral border of the scapula.

Insertion - on the lowest portion of the greater tuberosity of the humerus just below the infraspinatus.

Innervation - by the axillary nerve (NR C5, C6).

Action - is external rotation. It also acts eccentrically during the throwing motion to try and decelerate the rotation of the humerus.

Blood supply - from the circumflex scapular artery.

Rotate the cadaver to visulaize this muscle.

These muscles cover all of the glenohumeral joint, except the inferior aspect. All of them, except the supraspinatus, are rotators of the humerus. The rotator cuff protects the glenohumeral joint and gives it dynamic stability by contracting (dynamic) and holding the head of the humerus in the glenoid fossa of the scapula.

	If a person falls when the humerus is abducted, what happens to the head the humerus?
Since the cuff strengthens the glenohumeral joint everywhere except inferiorly, the head of the humerus may be levered out of the glenoid fossa, producing a dislocation of the glenohumeral joint (commonly referred to as a dislocated shoulder.