Muscle Actions - Video Tutorials & Practice Problems
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Muscle Actions
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5m
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As you learn different muscles, you'll see that different muscles can do different things depending on the movement. And so we're gonna say that muscles can take on different roles to perform a movement. And we have four different roles here that we're gonna talk about. The first one, we are gonna call the agonist or the prime mover. And you're likely to see both words there. So you should remember both agonist and prime mover for this one, the Agnes or the prime mover we're gonna say is gonna be the main muscle responsible for a move. And to highlight these different uh roles, we have the same sort of diagram drawn four times each time focusing on different muscles. And this diagram shows someone from the back showing the bones and the muscle and they are flexing at the elbow. So they're bending the arm like this, the muscle that is the prime mover for, that is going to be the biceps brachii, that sort of major muscle of the upper arm. So we can see that here, the origin is gonna be up in the shoulder and the insertion is down in the forearm there. When that muscle contracts, your forearm is gonna bend, you're gonna flex at the elbow. So we are gonna say the biceps and tracks. And when that happens that flexes the elbow joint, the biceps brachii is an agonist or a prime mover of that movement, right? For every agonist, there's an antagonist. So the antagonist is a muscle that opposes the action of the prime mover. And in this case at for flexing the elbow, that's gonna be the triceps, break eye. So we can see here the triceps break, I insert it in the back a little bit on the side of your arm. We can see the origins also up in the shoulder here. But the insertion here sort of goes back around the back of the elbow to the forearm. So when it contracts, it straightens the arm, this means to flex the arm, the tricep has to relax. So we're gonna say the triceps relaxes and that allows for flexion at the elbow. Remember, muscles can only contract. So for a prime mover to do something to do the opposite movement, it must have an antagonist and you can kind of test these out too on your own body. So for example, if you put your arm underneath the desk and you try to bend your elbow, you sort of lift up on the desk or the table that you're at, you should feel your bicep is sort of bulging, right? It's firm. If you feel your tricep. It probably feels pretty soft. It has to relax to allow that movement. Now, you can do the opposite. You can put your arm on top of the table or the desk and push down again. Don't do this with your whole arm. Just really try and straighten or bend at the elbow as you push down. You should feel the tricep, feels pretty firm. It's bulging, it's a prime mover for extension at the elbow right now. The bicep, it should be pretty soft. Now, just to be clear, the antagonist doesn't always relax completely. Sometimes it opposes a little bit just to sort of control and stabilize the movement. But agonists and antagonists work in opposition. All right, we have antagonists, we can also have synergist and synergist is something that is going to aid the prime mover. Muscles don't work by themselves. A lot of times, a lot of muscles work together to make a movement happen. So if we're talking about the biceps, brachii, it's a prime mover for flexing at the elbow. Well, another muscle that flexes at the elbow is the brachialis. And we can see here, brachialis has an origin on the humerus there and an insertion uh down on the form as well. So we are gonna say that the brachialis adds two, the amount of force. Now, sometimes determining which is the prime mover and which is the synergist doesn't really make sense. Sometimes they're just both working on a movement. So, distinguishing between those two isn't always helpful. Things work together as synergist. The brachialis also works as a prime mover for this movement, but it is a synergist to the biceps racial. All right, our final um type of movement here we're gonna say is a fixator. And you'll see we have fixated color coded the same as synergist. They're both purple here because sometimes fixators conti just considered a type of synergist, sometimes its own category. Sometimes it's considered sort of a subgroup of the synergist, but we'll talk about them separately here. A fixator is going to stabilize the origin of the prime mover. Remember the origin doesn't move in a muscle contraction, the insertion does, but a lot of your body parts move. So sometimes you have to hold the origin study, that's the job of the fixator. So for this, we have the rotator cuff illustrated and the rotator cuff is a group of muscles on the scapula that all insert sort of at the top of the humerus here. And we're just gonna say that the rotator cuff is going to brace the humorous. If you're doing this movement, you need the humorous to stay in place so that you can actually lift something. That's the job of a fixator. OK. Learning these again. Sometimes it just feels like another thing that you add, need to add on to the list of facts. But remembering these things together, understanding what an agonist is and what an antagonist is learning the biceps brachii with the triceps, break a understanding that they work in opposition. It's gonna help you understand all these movements much better and it's gonna help you understand it much more deeply. All right with that, we have an example to follow and more questions after that, I'll see you there.
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example
Muscle Actions Example 1
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3m
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Our example asks that for each action below, identify which of the two labeled muscles you would expect to be the agonist and which you would expect to be the antagonist. Then we need to state roughly where on the body would you expect to find a synergist for each of these movements? Right? So our first movement is lifting your arm to the side or abducting your arm. And we can see here in our anatomical model, we some see some bones and we see the deltoid and the Terry major label. All right. So just look at those two muscles where they're located relative the arm and see which one, which one do you think is the agonist for that movement of lifting your arm to the side or abducting your arm? Well, when I look, the deltoid is on top of the arm, these are, these are my two attachment points. And so as these two things get closer to each other, that arm is going to lift up. So this must be the insertion for the deltoid and this must be the origin of the deltoid. So I'm pretty sure that that deltoid must be my agonist. So I'm gonna write that in Agonist is my deltoid. Well, the antagonist again, I don't know much about these muscles at all so far. But if I just look where it is, the Terry Man is underneath the arm and if I try and get these two points where it attaches closer to each other, well, that'll pull the arm in the Terry Major. Must be an ad doctor to the humors. So, all right here, Terry Major. All right. Now, roughly, where would you expect a synergist of the deltoid to be? Well, if you're abducting your arm, you're lifting it away, then you'd expect that synergist to be on top of the shoulder would be my answer. So I'm gonna write synergist talk of shoulder. It's gonna work in a similar way to the deltoid. And sure enough, we have one more muscle uh drawn in here. This is the supraspinatus. It's part of your rotator cuff, but it runs across the scapula there, it runs underneath the deltoid and inserts on the top of the humerus there. And it is a synergist to the deltoid. All right, our next movement is smiling, right. So, let's look at this. We have two muscles, the Zygomaticus major. That's this muscle here attaching sort of on top, it looks like from the Zygomatic bone down to sort of the lips area it looks like. And then we have the mentalis. Remember mentalis, your mental region of your chin So it's this muscle down in here. So which one of those do you think is going to be the agonist for smiling? Well, to me, it looks like the Zygomaticus Major, right? It is on sort of the top of the mouth. So as these two points get closer to each other, it's gonna pull you into a smiling position. So, all right, as I go matter to, yeah, Zygomaticus Major, that means the antagonist. Well, that's got to be the mentalist and that makes sense, right? The mentalis is underneath the mouth. If you're gonna frown, you need to pull that down. So you need to relax the mentalis in order to smile. Now, where would a synergist be? Just sort of roughly? Well, I'd say a synergist has to probably be above the amount, right? If you're gonna pull the mouth into a smiling position, that muscle needs to be on top of the mouth to do it. And we can see here this creepy guy over my shoulder, he seems to be happy that we got the right answer.
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Problem
Problem
True or False: if false, choose the answer that best corrects the statement.
A fixator works to stabilize the insertion of the antagonist.
A
True.
B
False, the fixator stabilizes the origin of the agonist.
C
False, the fixator relaxes while the agonist contracts.
D
False, the fixator stabilizes the insertion of the agonist.
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Problem
Problem
The genioglossus is the primary muscle involved sticking out your tongue. The styloglossus is responsible for pulling the tongue back in, making it a(n) _______ for sticking out your tongue?
A
Agonist.
B
Synergist.
C
Antagonist.
D
Fixator.
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Problem
Problem
The soleus, gastrocnemius, and the tibialis anterior are all major muscles of the lower leg. The gastrocnemius and the soleus are both located in the posterior region of the calf, while the tibialis anterior is located in the anterior region of the lower leg. Based only on this information, which statement do you think is most likely true?
A
The gastrocnemius and the soleus are antagonists.
B
The soleus and the tibialis anterior are synergists.
C
The tibialis anterior is a fixator for the gastrocnemius and the soleus.
D
The gastrocnemius and the tibialis anterior are antagonists.