Chapter 7, Problem 1IP

Construct a chart listing all muscles crossing the glenohumeral joint according to whether they are superior, inferior, anterior, or posterior to the joint center. Note that some muscles may fall into more than one category. Identify the action or actions performed by muscles in each of the four categories.

Summary Introduction

To construct: Chart listing all muscles crossing the glenohumeral joint according to whether they are superior, inferior, anterior, or posterior to the joint center and identify the actions performed by the muscles listed in the four categories.

Concept introduction: Muscles are soft tissues. Muscles are classified as skeletal muscle, cardiac muscle, and smooth muscle. Skeletal muscles contract and relax with the bones and they help in locomotion, gait and respiration. The articulating connection also known as the joint is the connection between two bones that help both the bones to perform the same function in synchronized fashion.

Explanation of Solution

The glenohumeral joint is the major shoulder joint. It is a ball-and-socket joint that is formed by the articulation of humerus head with the glenoid fossa of the scapula. It is the most freely movable joint in the human body and the muscles associated with it help in the movement of the shoulder. It contributes in flexion, extension, abduction, adduction, medial and lateral rotation of the humerus.

The following chart shows the muscles of the glenohumeral joint, their location and function:

Glenohumeral joint muscles	Location	Action
Deltoid (Prime movers)	Anterior	Involved in flexion, medial rotation and horizontal adduction.
	Medial	Involved in abduction and horizontal abduction.
	Posterior	Involved in extension, horizontal abduction, and lateral rotation.
Pectoralis major (Prime movers)	Medial (Clavicular)	Involved in flexion, horizontal adduction, and medial rotation.
	Anterior (Sternal)	Involved in extension, medial rotation, adduction, and horizontal adduction.
Supraspinatus	Superior	Accessory muscles, involved in abduction and lateral rotation of the humerus.
Latissimus dorsi	Posterior	Prime movers, involved in extension, medial rotation, adduction, and horizontal abduction.
Teres major	Posterior	Accessory muscles, involved in extension, medial rotation, adduction, and adduction.
Infraspinatus	Inferior	Prime movers, Involved in lateral rotation.
Teres minor	Posterior	Involved in lateral rotation and horizontal abduction.
Subscapularis	Anterior	Involved in medial rotation.
Biceps brachii	Superior	Accessory muscles, long head is involved in abduction and short head is involved in flexion, adduction, horizontal adduction, and medial rotation.
Triceps brachii	Inferior	Accessory muscles, involved in extension and adduction.