Which muscle turns the palm upward or anteriorly?

Appeared in: WCL Staff Nurse - 2022

Explanation

The action of turning the palm upward or forward (anteriorly) is known as supination.
The supinator muscle, located in the posterior compartment of the forearm, is the prime mover for this action, especially in slow, unresisted movements.
The biceps brachii muscle, located in the anterior compartment of the arm, strongly assists in supination, particularly in fast movements or against resistance (e.g., turning a screw).

Option A: This muscle performs the opposite action, pronation, which involves rotating the radius over the ulna to turn the palm downward or posteriorly.
Option B: This is a circular (sphincteric) muscle located in the perineum that controls the voluntary closure of the anal canal. It is anatomically and functionally unrelated to the upper limb.
Option C: This is a deep muscle of the hip joint. Its function is to laterally (externally) rotate the thigh. It has no action on the forearm or hand.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomy and function of forearm muscles involved in supination and pronation as background academic context rather than a clinical decision trigger.
Nurses must understand these muscle actions when assisting patients with range-of-motion (ROM) exercises, positioning limbs to prevent contractures, or assessing neuromuscular injuries.
Injury to the radial nerve (specifically its deep branch, the posterior interosseous nerve) can weaken or paralyze the supinator muscle. This results in difficulty turning the palm up, impacting daily activities like turning a doorknob, holding a bowl of soup, or receiving change.
What if? If a patient had a median nerve injury instead, their ability to pronate the forearm (turn the palm down) would be compromised due to paralysis of the pronator teres and pronator quadratus, while supination would remain largely intact.

How to Approach the Question

First, identify the specific action described in the question: 'turns the palm upward or anteriorly'. Recognize this as the definition of supination.
Next, analyze the names of the muscles provided in the options. The name 'supinator' directly corresponds to the action of supination, making it a strong candidate.
Evaluate the other options to confirm they are incorrect. The name 'pronator' suggests the opposite action (pronation).
Recognize that 'External anal sphincter' and 'Obturator externus' are muscles of the pelvis and hip, respectively. Their location makes them anatomically irrelevant to forearm movement.
Conclude by selecting the option whose name and known function directly match the action described in the stem.

Concept Tested & Keywords

Concept Tested: Anatomy and function of forearm muscles involved in supination and pronation.
Stem keywords: muscle, palm upward, anteriorly
Lead-in keywords: Which

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E6 Anatomy Grays 43e Vol 2 Part 2 p. 130-131

Practise the full WCL Staff Nurse - 2022

Attempt every question from this paper in a timed mock, then review the full solution for each one.