Axillary nerve supplies?

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2021

Explanation

The axillary nerve originates from the posterior cord of the brachial plexus, with root values C5 and C6.
It provides motor supply to the deltoid muscle, which is the primary abductor of the arm at the shoulder joint (from 15 to 90 degrees).
It also innervates the teres minor muscle, one of the four rotator cuff muscles, which is responsible for the external (lateral) rotation of the arm.

Option A: This option is partially correct as the axillary nerve does supply the deltoid. However, the teres major muscle is not supplied by the axillary nerve.
Option C: This option is incorrect. The teres major is supplied by the lower subscapular nerve, and the subscapularis muscle is supplied by the upper and lower subscapular nerves.
Option D: This option is incorrect. Both the coracobrachialis and biceps brachii are muscles of the anterior compartment of the arm and are innervated by the musculocutaneous nerve.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Innervation of shoulder muscles by the axillary nerve as background academic context rather than a clinical decision trigger.
Assessing axillary nerve function is a critical part of the neurological examination after shoulder trauma, such as an anterior dislocation or fracture of the surgical neck of the humerus.
A key clinical sign of axillary nerve palsy is the loss of the rounded contour of the shoulder due to deltoid muscle atrophy, along with an inability to abduct the arm from 15 to 90 degrees.
Nurses must check for sensation over the 'regimental badge' area (skin over the lower deltoid) to test the sensory component of the axillary nerve.

How to Approach the Question

First, identify the core anatomical structure in the question: the 'axillary nerve'.
This is a direct recall question. Access your knowledge of the brachial plexus and its terminal branches.
Recall the motor innervation of the axillary nerve. It supplies two key muscles in the shoulder region.
Systematically evaluate each option. Option A includes teres major (incorrect). Option C includes two muscles not supplied by the axillary nerve. Option D includes muscles from the anterior arm compartment (incorrect).
Confirm that the chosen option correctly lists the two muscles innervated by the axillary nerve.

Concept Tested & Keywords

Qit2wg25A8uR7g_GjQz8m

E6 Anatomy Grays 43e Vol 2 Part 2 pp. 113-115, 105-107, 101-103

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