Match the muscles that move the arm with their actions.
1. Prime mover of arm extension
2. Flexes arm
3. Prime mover of arm flexion
4. Extends and adducts arm
5. Medially rotates arm
Latissimus dorsi
Pectoralis major
Triceps brachii (long head)
Biceps brachii (long head)
Subscapularis
The correct answer and explanation is:
Matched Muscles and Actions
- Prime mover of arm extension: Latissimus dorsi
- Flexes arm: Biceps brachii (long head)
- Prime mover of arm flexion: Pectoralis major
- Extends and adducts arm: Triceps brachii (long head)
- Medially rotates arm: Subscapularis
Explanation:
1. Latissimus dorsi – Prime mover of arm extension
The latissimus dorsi, a large, flat muscle on the back, is the primary muscle responsible for arm extension. It pulls the arm backward at the shoulder joint, an essential action in activities such as swimming or pulling. Its extensive origin and strong leverage make it a powerful extender.
2. Biceps brachii (long head) – Flexes arm
The biceps brachii has two heads, with the long head originating at the supraglenoid tubercle of the scapula. While its primary function is elbow flexion and supination of the forearm, it also assists in shoulder flexion due to its attachment at the shoulder joint. This dual function is particularly noticeable when lifting or pulling.
3. Pectoralis major – Prime mover of arm flexion
The pectoralis major is the largest chest muscle, contributing significantly to arm flexion. It pulls the arm forward at the shoulder, as in throwing or pushing. Its clavicular head is especially involved in initiating flexion from an extended position.
4. Triceps brachii (long head) – Extends and adducts arm
The long head of the triceps brachii extends and adducts the arm at the shoulder joint. Originating from the infraglenoid tubercle of the scapula, it crosses both the shoulder and elbow joints, contributing to backward arm movement and adduction.
5. Subscapularis – Medially rotates arm
The subscapularis, part of the rotator cuff group, is responsible for medially rotating the humerus. It stabilizes the shoulder and enables inward rotation, crucial in activities like reaching across the body or throwing a ball underhanded.