Structures of the Arm (Nursing)

00:01 So this brings us to the arm or brachium and by arm, we don't mean the entirety of the upper limb like we tend to say in everyday language.

00:12 We really mean just the portion between the shoulder and the elbow. Technically, anatomically speaking, that's the arm.

00:19 After the elbow, we have the forearm and we distinguish between the two.

00:25 And we're going to start with the anterior view and we're going to talk about the compartments of the arm from these views, anterior versus posterior. And in general, when I say what they do as a group of muscles although it's always important to keep in mind if a muscle crosses a joint, it can have an action at that joint and conversely if it doesn't cross a joint, it can't act on that joint.

00:49 And we'll see some examples of that right away in the upper limb.

00:54 Generally speaking, the anterior compartment, the anterior muscles of the arm, are going to cause flexion but it's going to depend, again, on which joint it crosses.

01:06 So let's put some of these in. We have the coracobrachialis.

01:13 So brachia means arm so we know that it's going to go to the humerus.

01:17 Coraco refers to another projection of the scapula called the coracoid process so we know that it's crossing the shoulder joint and so it's going to indeed flex the shoulder.

01:30 Then we have the brachialis which we see is not crossing the shoulder.

01:35 It's crossing the elbow and that means it's going to cause flexion at the elbow joint but do nothing at the shoulder joint.

01:44 And then, finally, we'll put on the largest more superficial, the biceps brachii.

01:49 We say brachii, biceps brachii, brachii referring to the arm.

01:53 Biceps meaning two heads and you can see there's two little tendons proximally because there's two heads of the muscle.

02:02 One's long and crosses the shoulder joint and the other is short, crosses the shoulder joint but to a different portion of the scapula but you can also notice that it crosses the elbow joint.

02:15 And we'll see the elbow joint in a different section but for now, we can see it crosses both joints which means it can have the action of flexion both at the shoulder and at the elbow.

02:27 As a rule of thumb, you can test for yourself if it's a muscle you can palpate, carry out a motion, and when you're palpating that muscle, you should either feel it contract or relax and if it's contracting as you're doing that motion you can say, "Hey, yeah, the biceps brachii is causing flexion at the elbow and also at the shoulder." Let's swing around to the posterior side and look at these posterior muscles of the brachium.

02:56 It's the same idea when we say triceps.

02:59 Triceps just means we have three heads to this very large muscle on the posterior arm and this also crosses the shoulder and the elbow and the heads that cross the shoulder are going to allow extension at the shoulder and the rest that crosses the elbow is going to cause extension at the elbow.

03:21 So sometimes because these are opposite movements, we would say the biceps and triceps are antagonistic muscles.

03:28 They get along just fine, it's just that they have opposite movements.