List all six possible movements that can occur at the shoulder joint and name the prime mover(s) of each movement. Then name their antagonists.
The correct answer and explanation is:
The shoulder joint is a ball-and-socket joint, offering a wide range of motion. There are six primary movements that can occur at the shoulder joint. Here is a breakdown of each movement, the prime movers responsible, and their antagonists:
- Flexion:
- Prime movers: Deltoid (anterior part), Pectoralis major (clavicular head)
- Antagonists: Latissimus dorsi, Teres major, Deltoid (posterior part)
Explanation: Flexion of the shoulder involves moving the arm forward, reducing the angle between the arm and the body. The anterior deltoid and the upper part of the pectoralis major are primarily responsible for this motion. The muscles that oppose this movement are the latissimus dorsi and teres major, which are involved in shoulder extension.
- Extension:
- Prime movers: Latissimus dorsi, Teres major, Deltoid (posterior part)
- Antagonists: Deltoid (anterior part), Pectoralis major (clavicular head)
Explanation: Extension at the shoulder joint occurs when the arm moves backward. The latissimus dorsi, teres major, and posterior deltoid are the primary muscles involved in shoulder extension. The antagonists to this action are the anterior deltoid and pectoralis major, which are involved in shoulder flexion.
- Abduction:
- Prime movers: Deltoid (middle part), Supraspinatus
- Antagonists: Pectoralis major, Latissimus dorsi, Teres major
Explanation: Abduction involves moving the arm away from the midline of the body. The deltoid (especially the middle portion) and supraspinatus muscles are responsible for initiating this movement. The muscles that oppose abduction are the pectoralis major, latissimus dorsi, and teres major, which are involved in adduction.
- Adduction:
- Prime movers: Pectoralis major, Latissimus dorsi, Teres major
- Antagonists: Deltoid (middle part), Supraspinatus
Explanation: Adduction is the movement of the arm towards the midline of the body. The pectoralis major, latissimus dorsi, and teres major are responsible for adduction. The deltoid (middle part) and supraspinatus act as antagonists to this movement.
- Medial Rotation:
- Prime movers: Subscapularis, Latissimus dorsi, Pectoralis major, Teres major
- Antagonists: Infraspinatus, Teres minor, Deltoid (posterior part)
Explanation: Medial rotation of the shoulder involves turning the arm inward, toward the body. The subscapularis, latissimus dorsi, pectoralis major, and teres major are the muscles responsible for this motion. The infraspinatus, teres minor, and posterior deltoid are the antagonists, as they are involved in lateral rotation.
- Lateral Rotation:
- Prime movers: Infraspinatus, Teres minor, Deltoid (posterior part)
- Antagonists: Subscapularis, Latissimus dorsi, Pectoralis major, Teres major
Explanation: Lateral rotation occurs when the arm rotates outward, away from the body. The infraspinatus, teres minor, and posterior deltoid are responsible for this movement. The muscles that oppose lateral rotation are the subscapularis, latissimus dorsi, pectoralis major, and teres major, which are involved in medial rotation.
Each movement is governed by a combination of muscles that work together to allow for a wide range of motion while maintaining stability at the shoulder joint. The antagonistic muscles serve to counterbalance the prime movers and ensure coordinated and controlled movements.