Origin and Insertion - Online Tutor, Practice Problems & Exam Prep

Origin and Insertion

Every skeletal muscle basically has two ends where it attaches to the skeleton, and when the muscle contracts, those two ends are going to get closer to each other. We're going to define those two ends as the origin and the insertion. So you can kind of think of the job of a muscle is to make two parts of the body get closer to each other. And when we do that, we're going to get the origin and the insertion closer. And specifically, we can say that the insertion, we're going to say the origin is the stationary attachment site. It doesn't move. The insertion, that's the mobile attachment site. That's the attachment site that moves. To see what we're talking about here, we have a diagram showing the bicep brachii. Now, bicep brachii, that's that sort of major muscle of your upper arm and has two attachment points. One's up in the shoulder and one's down here on the forearm. Well, if I flex my bicep brachii, my forearm is going to come up, my elbow is going to bend, and my forearm is going to keep on getting closer to my shoulder. The insertion moved closer to the origin. That means that the insertion must be down here on my forearm, and the origin didn't move, that's up in my shoulder. A little memory tool to keep these straight in your head, you can say the origin observes and the insertion inches closer. Now, learning the origin and insertion can sometimes just feel like another thing on the list of facts you got to memorize, but if you understand how a muscle works, they kind of just make sense. If you know the origin and the insertion, you should be able to figure out the movement of the muscle. If you know the movement of the muscle, you can often figure out the origin and the insertion. That's because the origin and the insertion are going to determine the movement. And to see what I mean, we have some examples here. We're going to show flexion at the knee. So here, this person is bending their knee, and their lower leg is sort of bending up, and they're using their bicep femoris. This is a muscle of a hamstring. You can see this has some attachment points up here on this end. One attachment point's on the ischium, and the other's on the back of the femur there. And then on the other end, it has an attachment point on the tibia and the fibula on the other side of the knee there. So, one way you can think of this movement of flexion is, well, you're getting your tibia and your fibula closer to your rear end. So, which end is moving? Well, down here on the tibia and fibula, that's moving. That's my insertion. I'm going to mark it with an I. The part that isn't moving, that's the origin. I'm going to mark it with an O. Next, we can look at extension. Extension is straightening the leg here. Sort of, straightening the leg at the knee. And we can see here we have a muscle that does that. That's the vastus intermedius. We have two attachment points for this muscle. One is on the front of the femur, and the other one sort of comes over the kneecap there, and attaches to the tibia at the tibial tuberosity. So, one way to think of extension is you're sort of getting the front of your tibia closer to the front of your femur. So, which part is moving? Well, that tibial tuberosity is moving, so that's going to be my insertion. The front of the femur is not moving, so that's going to be my origin. And I'll mark those. We can look at abduction. Abduction is taking an arm or a leg away from the midline of the body. So here we have the muscle, the gluteus medius, and this is attached up on the ilium and it's also attached on the greater trochanter. So, to pull the leg away like this, we can see here the greater trochanter of the femur. You can think of it as getting closer to the ilium. That's the job of this muscle. So, which part's moving? Well, the insertion moves. That's gotta be on the greater trochanter. I'll mark it with an I. The ilium does not move, so that's gotta be my origin. I'll mark it with an O. For adduction, adduction is bringing an arm or leg closer down into the midline of the body. Here, we're looking at the adductor longus muscle, and this attaches to the pubis and also to the femur down here. So, to bring this leg in towards the body, one way you can think of that, you're kinda taking the inside of your femur and moving it closer to the pubis. Well, which part's moving? The femur is moving, so that is going to be my insertion. The pubis isn't moving, so that's going to be my origin. Alright. Our last example here is going to be rotation. And for rotation, we're taking this leg and we're turning it out. So, you're sort of taking your foot and turning it out. And the muscle we're looking at here is the piriformis. And the piriformis has one attachment point on the sacrum and another on that greater trochanter, on the outside of the femur. So, one way you can think of this movement, that outside of the femur, that greater trochanter, is getting closer to the sacrum when you turn your leg out. That means that the insertion must be on that greater trochanter, and the origin must be on the sacrum. Alright. Again, trying to learn your origins and insertions of muscles on their own can sometimes just feel like a really unrelated list of facts. Remember, they cause the movements. So, if you know the origin and insertions, you know the movement. If you know the movement, you can usually figure out the origin and insertion.

Origin and Insertion Example 1

We see here that the origins and insertions of different muscles are given, and we want to know what type of movement or movements would be created when these muscles contract. So our first muscle here is a muscle of the abdomen, that's the rectus abdominis, and it says that the origin is on the pubis. So I'm going to go ahead and write an 'o' down by the pubis here, and the insertion is on the xiphoid process, that lowest part of the sternum, so I'm going to put an 'I' up there. And remember, our movement, we move the insertion towards the origin. So we're going to move it this way. So if I try and do that, if I try and move my xiphoid process closer to my pubis, I'm going to bend over forward. The more technical way to say that is that I'm going to say that I would flex the spine. Flexion of the spine or to flex the spine, that would be the movement of the rectus abdominis. Alright.

Our next example: this is the sternocleidomastoid muscle here. This is the muscle that sort of wraps around the front of your neck that you can kind of grab onto. And it says that my origin of this muscle is at the manubrium. That's that sort of top part of the sternum there, so I'll put an 'o' there. It also has an origin on the clavicle, but that's right next to it, so it doesn't really change anything. The insertion is going to be on the mastoid process. That's right here. That's that sort of bump right behind your ear there. Well, we're going to try and get this insertion closer to the origin for the movement. Well, if I just worry about my right one here, if I try and get my mastoid process closer to my sternum, I've got to go. So I kind of did two movements there. I rotated my head and I flexed my net. So I'm going to say rotate head, and flex. Alright.

Our third muscle here, we have the adductor longus muscle. Adductor longus has this origin. The origin is on the pubis, so I'll write an 'o' up here. And the insertion is going to be on the linea aspera of the femur. That's that line sort of going down the back of the femur. So if you try and move the back of your femur closer to your pubis, you'd be sort of pulling the leg in. Pulling the leg in towards the midline of the body. You would say that you are adducting or you'd say this muscle adducts the thigh. Alright. Again, understanding the origin and the insertion can tell you the movement of a muscle. And if you understand the movement of a muscle, you should be able to figure out at least pretty close to where those origin and insertions are. More practice problems to follow. Give them a try.

True or False: if false, choose the answer that best corrects the statement.

During a muscle contraction, the origin moves towards the insertion.

• A. True.
• B. False, the insertion moves towards the origin during contraction.
• C. False, both the origin and the insertion move during contraction.
• D. False, neither the origin nor the insertion moves during contraction.

The flexor carpi ulnaris is a muscle that adducts and flexes the hand at the wrist. The muscle attaches to both the humerus and the base of the 5th metacarpal. Based on the movement that this muscle performs, which attachment is the origin?

• A. Humerus.
• B. Wrist.
• C. 5th metacarpal.
• D. It's impossible to say from the information given.

The diagram below shows some of the muscles used for chewing. Using your knowledge of the bones, identify the insertion of the masseter.

• A. Temporal Bone.
• B. Zygomatic.
• C. Mandible.
• D. Maxilla.