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Functions of the vastus intermedius muscle

Functions and anatomy of the vastus intermedius muscle shown with 3D model animation.

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Hello everyone! It's Megan from Kenhub here, and in today's tutorial, we'll be covering the functions of the vastus intermedius muscle, and you can now see this muscle isolated on your screen.

The vastus intermedius muscle is one of four constituent parts of the largest and one of the most powerful collective muscles in the body – the quadriceps femoris. This muscle is located in the lower limb in the anterior compartment of the thigh or at the front of your thigh as you can see in the image on your screen. the vastus intermedius lies under or, in anatomical terms, deep to the rectus femoris which is the muscle that we're removing now and has the vastus medialis and vastus lateralis to either side of it. You can see on the screen the position of the vastus intermedius in relation to the other quadriceps muscles.

Now, all muscles of the anterior compartment of the thigh are innervated by the femoral nerve and the vastus intermedius is no exception. Useful knowledge for practical exams are the root values of the posterior division of the femoral nerve which innervates the vastus intermedius. These root values are L3 and L4.

The vastus intermedius has its proximal attachment or origin on the upper two-thirds of the shaft of the femur on the anterior and lateral surfaces. It then continues distally as part of the quadriceps tendon which in turn continues as the patellar ligament and inserts into the tibial tuberosity.

In terms of the actions of the vastus intermedius, this muscle acts specifically on the knee. The vastus intermedius acts with the other muscles of quadriceps femoris to extend the knee. So, understandably, anatomists often referred to the quadriceps femoris muscles as the great extensors of the knee.

If we consider the knee joint in a flexed position as is shown on your screen, we can see that extension of the knee joint straightens the lower limb increasing the angle between the posterior thigh and the leg. This is the action that the vastus intermedius is involved in – extension of the leg at the knee joint.

The functions of the vasti muscles of quadriceps femoris are tricky to isolate which is not difficult to understand given the intimate relationship between these muscles. The action of the vastus intermedius as part of the quadriceps femoris allows the body to undertake action such as climbing and walking upstairs. It also helps when lifting or moving the body's weight such as rising from a sitting position. All of these actions require extending the leg at the knee joint.

So, in summary, the vastus intermedius muscle works as part of the quadriceps femoris and is responsible for extension of the leg at the knee joint. The vastus intermedius helps facilitate movement such as walking upstairs and rising from a sitting position.

So that concludes our tutorial on the functions of the vastus intermedius muscle. Thanks for watching and see you next time.

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