Multiple Choice
Which muscle, highlighted in the diagram and known to work synergistically with the latissimus dorsi, is being identified?
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9. Muscle Tissue
Introduction to Muscles and Muscle Tissue
Multiple Choice
Which of the following is the major abductor muscle of the upper arm?
A
Biceps brachii
B
Deltoid
C
Latissimus dorsi
D
Pectoralis major
Verified step by step guidance1
Step 1: Understand the term 'abductor muscle'—an abductor muscle is responsible for moving a limb away from the midline of the body. In this case, the upper arm is being moved away from the torso.
Step 2: Review the anatomy of the upper arm and shoulder region. The major muscles involved in arm movement include the deltoid, biceps brachii, latissimus dorsi, and pectoralis major.
Step 3: Analyze the function of each muscle:
- The deltoid muscle is primarily responsible for abduction of the arm at the shoulder joint.
- The biceps brachii is involved in flexion and supination of the forearm, not abduction.
- The latissimus dorsi is responsible for adduction, extension, and internal rotation of the arm.
- The pectoralis major is involved in adduction and flexion of the arm.
Step 4: Identify the muscle that matches the function of abduction. Based on the analysis, the deltoid muscle is the major abductor of the upper arm.
Step 5: Confirm the answer by recalling that the deltoid muscle has three distinct parts (anterior, middle, and posterior fibers), with the middle fibers being primarily responsible for arm abduction.
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