Muscles of chest, shoulder and brachium SELF TEST- MUSCLES OF THE CHEST, SHOULDER AND BRACHIUM Modified True False. Indicate if each of the following statements is true. Make each incorrect statement correct by replacing the underlined words with the correct word or phrase:
1. Cardiac muscle tissue has branching fibers.
2. Smooth muscle has spindle-shaped cells with single nuclei in each cell.
3. The organs of the muscular system are composed of skeletal muscle tissue.
4. Skeletal muscle is voluntary and has prominent striations.
5. Cardiac muscle tissue is found in the walls of most visceral organs.
6. Intercalated discs are found only in smooth muscle tissue.
7. The proximal part of the upper limb is called the arm or brachium. Between the skin and the muscle mass is a layer of connective tissue called the deep fascia.
8. The tendon of a muscle attached to the more movable of two bones is called the tendon of insertion.
9. Distinct tendons are always present on muscles.
10. The biceps brachii is an antagonist to the triceps brachii.
11. Muscles with their origins on the axial skeleton and their insertions on the appendicular skeleton are called intrinsic muscles.
12. The brachialis anticus (-brachialis) muscle inserts on the radius.
13. The trapezius muscle, in the human, inserts on the ulna.
14. Three muscles in the cat represent the single trapezius muscle of humans. Major muscles inserting on the vertebral border of the scapula include the serratus anterior and levator scapulae.
15. The supraspinatus, infraspinatus, teres minor and the coracobrachialis are rotator cuff muscles.
16. The triceps brachii has its insertion on the olecranon process of the ulna.
17. The layer of dense connective tissue covering the muscle mass of the forearm is the antebrachial fascia.
18. The action of adduction of the arm at the shoulder is caused by action of the pectoralis minor.
19. The antagonist of the brachialis muscle is the triceps brachii.
20. The trapezius muscle in humans originates on the acromion process, spine of scapula, and clavicle.
21. A muscle that flexes the elbow and supinates the hand is the biceps brachii.
22. The biceps brachii flexes the shoulder and extends the elbow.
23. 24.
The Correct Answer and Explanation is:
Self-Test Answers (True/False + Corrections):
- True – Cardiac muscle tissue has branching fibers.
- True – Smooth muscle has spindle-shaped cells with single nuclei in each cell.
- True – The organs of the muscular system are composed of skeletal muscle tissue.
- True – Skeletal muscle is voluntary and has prominent striations.
- False – Cardiac muscle tissue is found in the heart wall, not in the walls of most visceral organs.
- False – Intercalated discs are found only in cardiac muscle tissue, not in smooth muscle.
- True – The proximal part of the upper limb is the arm or brachium, and deep fascia lies between the skin and muscle.
- True – The tendon attached to the more movable bone is the insertion.
- False – Distinct tendons are not always present; some muscles insert directly into bone or via aponeuroses.
- True – The biceps brachii is an antagonist to the triceps brachii.
- False – Muscles with origins on the axial and insertions on the appendicular skeleton are extrinsic muscles, not intrinsic.
- False – The brachialis inserts on the ulna, not the radius.
- False – The trapezius muscle inserts on the clavicle and scapula, not the ulna.
- True – Cats have three trapezius muscles; the serratus anterior and levator scapulae insert on the vertebral border of the scapula.
- False – The coracobrachialis is not a rotator cuff muscle; it includes supraspinatus, infraspinatus, teres minor, and subscapularis.
- True – Triceps brachii inserts on the olecranon of the ulna.
- True – The antebrachial fascia covers the forearm muscles.
- False – Pectoralis major, not pectoralis minor, causes adduction of the arm.
- True – The antagonist of brachialis is triceps brachii.
- False – Trapezius originates on the occipital bone and vertebrae, not on the acromion, spine, or clavicle (those are insertions).
- True – Biceps brachii flexes the elbow and supinates the hand.
- False – Biceps brachii flexes both the shoulder and the elbow, not extend.
23 & 24: Correct Answers + 300-word Explanation
23. Name a muscle that originates on the clavicle and inserts on the humerus.
Correct Answer: Deltoid
24. Name a muscle involved in internal rotation of the humerus.
Correct Answer: Subscapularis
Explanation:
The deltoid muscle is a major shoulder muscle with multiple origins and functions. It originates on the clavicle, acromion, and spine of the scapula, and inserts on the deltoid tuberosity of the humerus. This muscle is divided into anterior, middle, and posterior fibers. The anterior deltoid, which originates on the clavicle, assists in flexion and internal rotation of the arm. Its wide origin and narrow insertion allow it to generate a range of movements at the glenohumeral joint, particularly abduction.
The subscapularis, on the other hand, is one of the four rotator cuff muscles, and its primary role is internal (medial) rotation of the humerus. It originates from the subscapular fossa of the scapula and inserts on the lesser tubercle of the humerus. It plays a vital role in stabilizing the shoulder joint by keeping the head of the humerus firmly within the glenoid cavity during shoulder movements. Without it, the shoulder would be prone to dislocation during dynamic activities.
Together, these muscles highlight the complexity of shoulder mechanics. The deltoid allows for large, visible movements like lifting the arm, while the subscapularis contributes to the fine-tuned, stabilizing functions necessary for joint health and efficient biomechanics. Understanding the origin and insertion of these muscles helps in diagnosing injuries, planning surgeries, and designing rehabilitation protocols in clinical settings.
