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.
We really mean just the portion between the shoulder and the elbow.
Technically, anatomically speaking, that's the arm.
After the elbow, we have the forearm
and we distinguish between the two.
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.
And we'll see some examples
of that right away in the upper limb.
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.
So let's put some of these in.
We have the coracobrachialis.
So brachia means arm so we know
that it's going to go to the humerus.
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.
Then we have the brachialis
which we see is not crossing the shoulder.
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.
And then, finally, we'll put on the largest
more superficial, the biceps brachii.
We say brachii, biceps brachii,
brachii referring to the arm.
Biceps meaning two heads and you can see there's two little tendons proximally
because there's two heads of the muscle.
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.
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.
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.
It's the same idea when we say triceps.
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.
So sometimes because these are opposite movements,
we would say the biceps and triceps are antagonistic muscles.
They get along just fine,
it's just that they have opposite movements.