Chapter 10 - Section 10.4 - Study Guide - Assess Your Learning Outcomes - Page 371: 2

The muscles you've mentioned, which act on the humerus (the bone of the upper arm), play critical roles in various arm movements and shoulder stability. Here's an overview of each of these muscles and their functions: 1. **Pectoralis Major**: The pectoralis major, commonly referred to as the chest muscle, is responsible for flexing, adducting (bringing the arm toward the body), and internally rotating the humerus. It is involved in movements such as pressing, hugging, and pulling. 2. **Latissimus Dorsi**: The latissimus dorsi, or lats for short, is a large muscle of the back. It is responsible for extending, adducting, and internally rotating the humerus. This muscle is engaged in various pulling and lifting actions, like pull-ups and rowing exercises. 3. **Deltoid**: The deltoid muscle is a triangular-shaped muscle that covers the shoulder joint. It is responsible for several actions involving the humerus, including abduction (raising the arm away from the body), flexion (raising the arm forward), and extension (moving the arm backward). The deltoid provides a significant amount of shoulder strength and stability. 4. **Teres Major**: This muscle is located near the latissimus dorsi and works in conjunction with it. The teres major assists in adducting and internally rotating the humerus. 5. **Coracobrachialis**: The coracobrachialis muscle is a smaller muscle located near the front of the shoulder. It helps flex the humerus and stabilize the shoulder joint. 6. **Rotator Cuff (SITS) Muscles**: - **Supraspinatus**: This muscle is located in the upper part of the shoulder and assists in initiating abduction of the humerus. It helps lift the arm away from the body, especially during the first 15 degrees of this movement. - **Infraspinatus**: The infraspinatus muscle is located on the back of the shoulder blade (scapula) and is responsible for external rotation of the humerus. It helps to rotate the arm outward. - **Teres Minor**: Like the infraspinatus, teres minor is involved in the external rotation of the humerus and is also located on the back of the shoulder blade. - **Subscapularis**: This muscle is positioned on the front of the shoulder blade (scapula) and is responsible for internal rotation of the humerus. It allows you to rotate the arm inward. These muscles work together to perform a wide range of movements at the shoulder and arm, including lifting, pushing, pulling, and rotating the humerus. Proper coordination and balance between these muscles are essential for shoulder health and functional upper body movements.

The muscles you've mentioned, which act on the humerus (the bone of the upper arm), play critical roles in various arm movements and shoulder stability. Here's an overview of each of these muscles and their functions: 1. **Pectoralis Major**: The pectoralis major, commonly referred to as the chest muscle, is responsible for flexing, adducting (bringing the arm toward the body), and internally rotating the humerus. It is involved in movements such as pressing, hugging, and pulling. 2. **Latissimus Dorsi**: The latissimus dorsi, or lats for short, is a large muscle of the back. It is responsible for extending, adducting, and internally rotating the humerus. This muscle is engaged in various pulling and lifting actions, like pull-ups and rowing exercises. 3. **Deltoid**: The deltoid muscle is a triangular-shaped muscle that covers the shoulder joint. It is responsible for several actions involving the humerus, including abduction (raising the arm away from the body), flexion (raising the arm forward), and extension (moving the arm backward). The deltoid provides a significant amount of shoulder strength and stability. 4. **Teres Major**: This muscle is located near the latissimus dorsi and works in conjunction with it. The teres major assists in adducting and internally rotating the humerus. 5. **Coracobrachialis**: The coracobrachialis muscle is a smaller muscle located near the front of the shoulder. It helps flex the humerus and stabilize the shoulder joint. 6. **Rotator Cuff (SITS) Muscles**: - **Supraspinatus**: This muscle is located in the upper part of the shoulder and assists in initiating abduction of the humerus. It helps lift the arm away from the body, especially during the first 15 degrees of this movement. - **Infraspinatus**: The infraspinatus muscle is located on the back of the shoulder blade (scapula) and is responsible for external rotation of the humerus. It helps to rotate the arm outward. - **Teres Minor**: Like the infraspinatus, teres minor is involved in the external rotation of the humerus and is also located on the back of the shoulder blade. - **Subscapularis**: This muscle is positioned on the front of the shoulder blade (scapula) and is responsible for internal rotation of the humerus. It allows you to rotate the arm inward. These muscles work together to perform a wide range of movements at the shoulder and arm, including lifting, pushing, pulling, and rotating the humerus. Proper coordination and balance between these muscles are essential for shoulder health and functional upper body movements.