what are muscular Origins and insertions well typically when a muscle contracts it shortens like this through the myosin and act in myofilaments so but muscles don't exist by themselves in outer space or attached to Bones through tendons and so when a muscle contracts it pulls the bones together now here we have an example of the biceps we see it Contracting like this and so we see one attachments on the scapula bone and the others is on the radius bone and so we see that the bones can move and we call now the bone that doesn't move the origin and the bone that moves the insertion so the fixed bone is the origin and the mobile bone is the insertion the insertion typically moves towards the origin during muscular contraction a challenge is that Origins and assertions are not necessarily unchanging let me show you what I mean here's a muscle we're going to put a bone on one end we're going to Anchor it and this is usually anchored through other bones around it and or muscles so we call that the origin now the insertion is the bone the mobile bone that moves so we see that the insertion moves towards the origin when the muscle contracts but what happens if we stabilize the other bone so it becomes the origin and now the other bone is unstabilized so we call that the insertion and look now when the muscle contracts the other bone moves towards and so the origin insertions are not necessarily unchanging let's do that in an example here's a gluteus medius muscle when it contracts it a b ducts the femur so its origin is on the ilium and the insertion is on the femur the femur when it contracts moves towards the origin but what happens if we now stabilize the femur so it becomes the origin and now we can act on the ilium so the ilium or the insertion moves towards the origin like when you lift up that left leg off the ground and now the gluteus medius stabilizes the pelvis like that so here's the origin on the ilium and the insertions on the femur so when the muscle contracts the femur moves towards the origin but now let's take the origin and move it to the femur so now when the when the gluteus medius contracts is if you lift the opposite leg off the ground it stabilizes the pelvis so this is one of the reasons why I like to instead of using origin Insertion I use terms like proximal attachment and distal attachment because it gives this idea where students do not necessarily then get fixed that you can never change Origins and insertions and that my friends is Origins and insertions in a nutshell