|Muscles connecting the upper extremity to the vertebral column.|
|Gray's||subject #123 439|
|Origin:||clavicle, acromion, spine of the scapula|
|Insertion:||deltoid tuberosity of humerus|
|Artery:||primarily posterior circumflex humeral artery|
|Action:||shoulder abduction, flexion and extension|
The deltoid is a frequent site to administer intra-muscular injections.
It arises in three distinct sets of fibers:
From this extensive origin the fibers converge toward their insertion, the middle passing vertically, the anterior obliquely backward and lateralward, the posterior obliquely forward and lateralward; they unite in a thick tendon, which is inserted into the V-shaped deltoid tuberosity on the middle of the lateral aspect of the shaft of the humerus. At its insertion the muscle gives off an expansion to the deep fascia of the arm.
The anterior fibres are involved in shoulder abduction when the shoulder is externally rotated. The anterior deltoid is weak in strict transverse flexion but assists the pectoralis major during shoulder transverse flexion / shoulder flexion (elbow slightly inferior to shoulders).
The exterial fibres are strongly involved in transverse extension particularly since the latissimus dorsi is very weak in strict transverse extension. The posterior deltoid is also the primary shoulder hyperextensor.
The lateral fibres are involved in shoulder abduction when the shoulder is internally rotated, are involved in shoulder flexion when the shoulder is internally rotated, and are involved in shoulder transverse abduction (shoulder externally rotated) -- but are not utilized significantly during strict transverse extension (shoulder internally rotated).
The deltoid muscle has three sections, the front head, the side head and the rear head. These heads have different actions and so need different strength training exercises to completely train the whole of the muscle.
The Deltoid is a classical example of a multipennate muscle.
The middle fibres of the muscle arise in a bipenniform manner (like a bird's feather) from the sides of the tendinous intersections, generally four in number, which are attached above to the acromion and pass downward parallel to one another in the substance of the muscle. The oblique fibers thus formed are inserted into similar tendinous intersections, generally three in number, which pass upward from the insertion of the muscle and alternate with the descending septa. The portions of the muscle arising from the clavicle and spine of the scapula are not arranged in this manner, but are inserted into the margins of the inferior tendon.
Katharine Cheryl Pruter
The content of this section is licensed under the GNU Free Documentation License (local copy). It uses material from the Wikipedia article "Deltoid muscle" modified March 22, 2008 with previous authors listed in its history.