Before we get into the nitty-gritty in terms of the specific muscles there's some terminology that
we really need to make sure we understand before you move forward and the main things that I want
you to understand are the difference between origins and insertions okay so you can see the
terms here origin and insertion and a lot of times we've been moving away from these more traditional
terms of origin and insertion so oftentimes you'll hear the term proximal attachment so the more
proximal of the attachments or distal attachment and this is in particular when you're talking
about appendicular muscles so muscles associated with your appendages sometimes you can hear the
term superior attachment and inferior attachment they mean similar things is just in terms of the
position of the muscles so what what do these mean well typically the origin of a muscle is
where the tendon is attaching to the more stable bone okay so that's an important thing to note
typically we're talking about the attachment to the bone that's not moving whereas the insertion
is going to be the attachment to the bone that is going to be moving of the joint so let's
think about that when we think about our biceps muscle now the biceps muscle has two heads or
two proximal attachments these are attaching to the scapula here and you can see that right here
the scapula when the biceps brachii contracts doesn't move at all okay so that is going to be
the origins of that whereas the biceps brachii is going to attach to the radial tuberosity for
its insertion or distal attachment so when the biceps brachii contracts here it is going to
move the the radius or the forearm in order to allow for elbow flexion now that's what we
think that's kind of the schematic that you think of in terms of muscle attachments now
can the proximal attachment and the distal attachment switch in terms of their role so
reverse motion action absolutely so sometimes this can allow for some type of movement
in this region but typically when we say origin insertion we're talking about the main movement
of that muscle and for the biceps brachii that's going to be flexion of the elbow so typically that
insertion is going to be pulled towards the origin so if you think of that forearm flexing it's being
pulled towards the origin or the scapula here so why do we care about origins and insertions
well it gives you an idea of which particular joints that muscle is crossing and in order for
a muscle to play a role in terms of the joint or the action of a joint it has to cross that joint
now this is why we care this is why it's worth understanding all of these attachment sites one
other point that I really want to get across is that muscles can cross more than one joint so
it can play a role in more than one joint and that biceps brachii that we were just discussing it's
a really good example of that it's actually a three joint muscle so it can play a role in
terms of three joints the shoulder you can play a role in terms of flexion of the shoulder the
elbow this is its main action which is going to be flexion of the elbow as well as the proximal
radio-ulnar which is right next to the elbow joint actually within that articular capsule and so the
biceps brachii will actually be a very important supinator so here's a pronated supinated it will
play a role in terms of that so this is a really good example of a three joint muscle so now that
we have a good understanding in terms of the terminology as we get into the specifics of
the muscles play a keep note in terms of which particular joints these muscles are crossing