Deep Layer (AC) – Anatomy of the Forearm

by James Pickering, PhD

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    00:00 If we then look at the deep layer, we can see we've got some muscles which are lying deep to flexor digitorum superficialis.

    00:09 We have flexor digitorum profundus.

    00:13 We can see that this is coming from the ulna.

    00:16 It's also coming from the interosseous membrane that's between the two bones of the forearm, the radius and the ulna.

    00:24 And this again gives rise to four long tendons that this time go towards the distal phalanx of each digit, two to five, not including the thumb.

    00:36 The thumb is different because it has its own specific flexure and this is known as flexor pollicis longus.

    00:43 Pollicis meaning the thumb.

    00:45 Flexor pollicis longus.

    00:47 The fact that we call it flexor pollicis longus indicates is going to be a flexor pollicis brevis.

    00:54 And this muscle is within the hands. So we'll look at it later.

    00:57 The final muscle, the deep muscle in the anterior compartment is pronator quadratus.

    01:03 And that runs between the two distal ends of the radius and the ulna.

    01:08 So let's have a look at the attachment of these muscles.

    01:11 Flexor digitorum profundus is running from the proximal surfaces of the medial and anterior surfaces of ulna, and the interosseous membrane.

    01:22 So it's coming from the ulna.

    01:25 It then passes via its four long tendons to the distal phalanges, the medial four distal phalanges of digits 2, 3, 4, and 5.

    01:38 The nerve supply, it has a jewel nerve supply.

    01:42 The lateral muscle bellies, these the ones that are going to digits two, and three are supplied by the anterior interosseous nerve.

    01:50 And the tendons that are going to digits four and five are supplied by the ulna nerve.

    01:57 So flexor digitorum profundus has two nerves supplying it, the median nerve and the ulna nerve.

    02:06 Its function is to flex the hand at the wrist joints, and it also flexes the distal interphalangeal joint.

    02:13 So where flexor digitorum superficialis flex the proximal interphalangeal joint.

    02:19 This knife flexes the very distal interphalangeal joint.

    02:23 The joint between the distal phalanx and the middle phalanx.

    02:28 If we go back and look at flexor pollicis longus, we can see this is really coming from the radius.

    02:34 And this gives a long tendon that goes and attaches to the distal phalanx of the thumb.

    02:41 So we can see that flexor pollicis longus running from the anterior surface of the radius, and also the interosseous membrane passes to the distal phalanx of the first digit.

    02:51 First digit be in your thumb.

    02:54 The pronator quadratus, as we saw here, is running between the two distal ends of the radius and the ulna.

    03:01 It runs from the distal quarter of the ulna.

    03:04 So the last quarter of the ulna and it actually passes towards the radius.

    03:10 So when pronator quadratus contracts, it is actually going to move the radius.

    03:15 It is going to move the radius into a more pronated position.

    03:18 So from this supine position, contraction of pronator quadratus is going to protonate the radius, pronate the forearm.

    03:28 It pulls the radius over the ulna bone.

    03:31 Both flexor pollicis longus and pronator quadratus are innervated by the anterior interosseous nerve.

    03:40 And this is a branch of the median nerve.

    03:42 So the median nerve is supplying the majority of these muscles within the anterior compartment.

    03:48 But a specific branch the anterior interosseous nerve is supplying the flexor pollicis longus and pronator quadratus.

    03:58 Flexor pollicis longus does similar functions to flexor digitorum muscles except it acts at the first digit.

    04:06 Continued contraction will flex the wrist, it flexes the interphalangeal, and metacarpophalangeal joints associated with the first digit.

    04:17 Pronator quadratus pronates the forearm.

    04:20 So it acts on the radioulnar joints.

    About the Lecture

    The lecture Deep Layer (AC) – Anatomy of the Forearm by James Pickering, PhD is from the course Upper Limb Anatomy.

    Included Quiz Questions

    1. Anterior interosseous nerve (branch of the median nerve)
    2. Ulnar nerve
    3. Brachial nerve
    4. Radial nerve
    5. Musculocutaneous nerve
    1. Flexion of the distal interphalangeal joint
    2. Extension of the hand at the wrist joint
    3. Flexion of the proximal interphalangeal joint
    4. Extension of the metacarpophalangeal joint
    5. Extension of the distal interphalangeal joint

    Author of lecture Deep Layer (AC) – Anatomy of the Forearm

     James Pickering, PhD

    James Pickering, PhD

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    Lecturio is going to save my semester
    By vinzent V. on 04. March 2021 for Deep Layer (AC) – Anatomy of the Forearm

    Thank you for this video, loved how concise and precise it was