The video will begin our review of the
muscles of the upper extremity.
We will start off with the deltoid, the biceps brachii, the brachialis and the triceps brachii.
To begin with the deltoid, the proximal attachments differ based on which exact fibers you're
talking about.
The anterior fibers have their proximal attachment along the lateral 3rd of the clavicle.
The lateral fibers have their attachment along
the lateral border of the arcomion process.
And the posterior fibers have their attachment along the spine of the scapula.
Together these 3 fibers come to distally attach at the deltoid tuberosity of the humerus.
As the deltoid muscle shortens it is responsible for abduction of the arm but only after the
1st 15 degrees.
The supraspinatus muscle is responsible for
the 1st 15 degrees and we'll cover this in the next video.
The different fibers of the deltoid also have slightly different actions.
The anterior fibers because of their position on the anterior side of the body, also assist
with flexion of the arm at the shoulder, as well as medial rotation of the arm.
The posterior fibers because of their location
on the posterior side assist with extension of the arm at the shoulder as well as lateral
rotation.
You can see these actions taking place as shortening of the muscle is demonstrated.
The biceps brachii has its short head proximally attaching at the coracoid process of the scapula
and it's long head proximally attaching at the supraglenoid tubercle which is right there.
The 2 heads come together via a single tendon
to distally attach at the radial tuberosity of the radius.
As you can see, shortening of this muscle would cause flexion of the forearm.
Additionally, shortening of the muscle would cause supination at the radioulnar joint which
looks like this.
Finally, the biceps is also responsible for very weak flexion of the arm.
Because the biceps muscle crosses over 3 joints
with the long head traversing over the shoulder joint and both heads crossing the elbow joint
as well as the radioulnar joint, this muscle has 3 different actions.
The brachiallis muscle proximally attaches at the mid shaft of the humerus and distally
attaches at the coronoid process of the ulna, which is right here.
When this muscle shortens it is responsible
for flexion of the forearm at the elbow.
Each head of the triceps brachii has its proximal attachment at a different site.
The lateral head of the triceps has its proximal attachment along the upper half of the posterior
surface of the humoral shaft.
Along here.
The medial head has its proximal attachment along the posterior surface of the humerus
distal to the radial groove.
Right here.
And the long head has its proximal attachment at the infraglenoid tubercle of the scapula.
Right Here.
Together these three heads come together to attach at the olecranon process of the ulna.
Right here.
The triceps is largely responsible for extension of the forearm at the elbow.
You can see this happening as we move from a flexed position to an extended position.
It is also responsible because the long head has a proximal attachment that is proximal
to the shoulder joint.
It is able to enact some action at this joint
as well.
Namely, extension of the arm at the shoulder as well as some amount of adduction of the
arm.