Action
Contraction of the supraspinatus muscle leads to abduction of the arm at the shoulder joint. It is the main agonist muscle for this movement during the first 10-15 degrees of its arc. Beyond 30 degrees the deltoid muscle becomes increasingly more effective at abducting the arm and becomes the main propagator of this action.
The supraspinatus muscle is one of the musculotendinous support structures called the rotator cuff that surround and enclose the shoulder. It helps to resist the inferior gravitational forces placed across the shoulder joint due to the downward pull from the weight of the upper limb.
The supraspinatus also helps to stabilize the shoulder joint by keeping the head of the humerus firmly pressed medially against the glenoid fossa of the scapula.
For USMLE step 1, know that the supraspinatus initiates abduction of the shoulder. Without a functioning supraspinatus, the physician must start abducting the patient's arm and eventually the patient will be able to finish abduction if the deltoid is functional, which is common because the supraspinatus is innervated by the suprascapular nerve from the superior/upper trunk of the brachial plexus. The deltoid is innervated more distally by the axillary nerve, which arises from the posterior cord of the brachial plexus.
Read more about this topic: Supraspinatus Muscle
Famous quotes containing the word action:
“Economic depression can not be cured by legislative action or executive pronouncement.”
—Herbert Hoover (1874–1964)
“The United States must be neutral in fact as well as in name.... We must be impartial in thought as well as in action ... a nation that neither sits in judgment upon others nor is disturbed in her own counsels and which keeps herself fit and free to do what is honest and disinterested and truly serviceable for the peace of the world.”
—Woodrow Wilson (1856–1924)
“Power is action; the electoral principle is discussion. No political action is possible when discussion is permanently established.”
—Honoré De Balzac (1799–1850)