17 The Pectoral Girdle and Arm
Learning Objectives:
- Recognize the different categories of muscles with respect to movement.
- Describe the different types of muscle contractions
- Identify, describe, and palpate the joints of the pectoral girdle.
- Identify the rotator cuff muscles and describe their action, origin, insertion, and innervation.
- Identify and describe the posterior muscles acting on the shoulder girdle.
- Identify and describe the anterior muscles acting on the pectoral girdle.
Terms to Know
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Joints of the Pectoral Girdle
Muscles Acting on the Elbow
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Muscles Acting on the Pectoral Girdle
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Introduction
In this lab you will explore the joints and muscles of the pectoral girdle. As a study tip, you may find it helpful to write a description of each muscle/structure as you identify them. When you write it in your own words, it may spark your memory as you look for that structure the next time you study.
Lab Activities
Activity 1: Joints of the Pectoral Girdle and Shoulder
Examine the three joints of the pectoral girdle and shoulder and the structures listed with them.
- Observe the sternoclavicular joint. This is between the sternum and the clavicle. The sternoclavicular ligament helps to stabilize this joint. Palpate your own sternoclavicular joint.
- Observe the acromioclavicular joint. Palpate this joint on yourself, where the clavicle meets the acromion at the “point of your shoulder.” Observe the acromioclavicular, coracoacromial, and coracoclavicular ligaments. Notice how the supraspinatus runs underneath this ligament as it moves towards the greater tubercle.
- Observe the glenohumeral joint. Notice how smooth the articular cartilage on the head of the humerus is. Also, note how thick the articular capsule is. Lastly, observe the ring of tissue just surrounding the glenoid fossa. This is the glenoid labrum.
- Notice the scapulothoracic joint. This is not a true articulation. It is considered a functional joint between the scapula and the thoracic wall.
Activity 2: Muscles of the Pectoral Girdle and Shoulder
Explore the muscles of the pectoral girdle and arm listed below. You will be asked to identify the origins, insertions, actions, and/or innervations of these muscles listed in the muscle charts. However, you may not need to know certain specifics for each muscle. Follow what is on the posted muscle charts for the specifics of what you need to know for each muscle. It can be helpful for you to have the muscle charts with you while you are examining these structures. Looking at the orientation of muscle fibers and the origin/insertions can help you understand the actions of these muscles.
- Examine the trapezius. This muscle has fibers running superiorly, horizontally, and inferiorly from the vertebral column to insert onto the scapular spine, acromion, and clavicle.
- Observe the rhomboid major, rhomboid minor, and levator scapulae. The rhomboid major is larger and inferior to the rhomboid minor. The rhomboid minor is th