Study Guide - Quick Reference - Deltoids

Note: If you intend to do the activities below do not open the "Study Guide" - all the answers are already filled in.  The study guide is just a quick reference tool, similar to flash cards - great for preparing for an exam.

Introduction:

In this lecture we will be discussing Deltoids:

Etymology:

• deltoid (adj.) 1741, in deltoid muscle, so called for its shape, from Greek deltoeides "triangular," literally "shaped like the letter delta;" see delta + -oid. (Etymology Online)

The deltoid is commonly divided into 3 distinct parts based on function, fiber arrangement, neural innervation, and distinct separation at the proximal attachment.  The 3 divisions are:

• Anterior Deltoid
• Middle Deltoid (There is no such thing as a "medial" deltoid)
• Posterior Deltoid

What joint do these muscles cross?

These muscles originate on the distal third of the clavicle, acromion process and spine of the scapula, and insert into the deltoid tuberosity of the humerus.  These muscles cross the shoulder (glenohumeral joint) and assist in motion of the arm.  They have no attachment to the rib-cage or torso, so unlike our Axial Scapular Muscles, under most normal circumstances the deltoids cannot move the scapula and shoulder girdle.  Before we start analyzing the function of each muscle, make a word bank for yourself.  What are the joint actions of the shoulder/glenohumeral joint? The muscles in this lecture must perform joint actions in this word bank… they cannot perform any other actions.  For example, there is no such thing as retraction of the shoulder/glenohumeral joint.

• Frontal Plane Joint Actions:
• Transverse Plane Plane Joint Actions:
• Sagittal Plane Plane