Description

This video covers the muscles of the forearm, including their origins, insertions, and functions.

Muscles of the Forearm

• Anterior (Flexor) Group
• Lateral (Radial) Group
• Posterior (Extensor) Group

Anterior (Flexor) Group

1st Layer

• Palmaris Longus
• Flexor Carpi Radialis
• Pronator Teres
• Flexor Carpi Ulnaris

2nd Layer

• Flexor Digitorum Superficialis

3rd Layer

• Flexor Digitorum Profundus
• Flexor Pollicis Longus

4th Layer

• Pronator Quadratus

Pronator Quadratus (Musculus Pronator Quadratus)

• Origin: Anterior surface of Ulna
• Insertion: Anterior surface of Radius
• Function: Pronation of forearm

Flexor Digitorum Profundus (Musculus Flexor Digitorum Profundus)

• Origin: Anterior surface of Ulna
• Insertion: Base of distal phalanges (2-5 fingers) (Basis Phalangis Distalis II-V)
• Function:
  • Flexion of 2-5th fingers at metacarpophalangeal and interphalangeal joints
  • Accessory flexion of hand

Lateral (Radial) Group

Superficial Layer

• Brachioradialis
• Extensor Carpi Radialis Longus
• Extensor Carpi Radialis Brevis

Deep Layer

• Supinator

Supinator (Musculus Supinator)

• Origin: Lateral Epicondyle, Radial Collateral Ligament, Ulna
• Insertion: Lateral Surface of Radius
• Function: Supination of forearm

Posterior (Extensor) Group

Superficial Layer

• Extensor Digitorum
• Extensor Digiti Minimi
• Extensor Carpi Ulnaris

Deep Layer

• Abductor Pollicis Longus
• Extensor Pollicis Brevis
• Extensor Pollicis Longus
• Extensor Indicis

Abductor Pollicis Longus (Musculus Abductor Pollicis Longus)

• Origin: Posterior surface of Ulna/Radius, Interosseous membrane
• Insertion: Base of 1st metacarpal
• Function: Abduction of thumb

Extensor Pollicis Brevis (Musculus Extensor Pollicis Brevis)

• Origin: Posterior surface of Radius, Interosseous membrane
• Insertion: Base of proximal phalanx of thumb
• Function: Extension and abduction of thumb

Extensor Indicis (Musculus Extensor Indicis)

• Origin: Posterior surface of Ulna, Interosseous membrane
• Insertion: Base of middle/distal phalanx of index finger
• Function: Extension of index finger (2nd finger)

Extensor Digitorum (Musculus Extensor Digitorum)

• Origin: Lateral Epicondyle of Humerus
• Insertion: Base of middle and distal phalanges of 2-5th fingers
• Function:
  • Abduction of fingers
  • Extension of hand

Transcript

Introduction
0:03
What’s up. Meditay here and now we’ll be covering the muscles of the forearm, which as you know
0:08
are a part of the upper limb. Alright. So, the muscles of the upper limb are divided into 4
0:13
parts according to their anatomical location. The first group are muscles of the shoulder joint.
0:18
Then we have the muscles of the arm, muscles of the forearm and then the muscles of the hand.
Division of the Forearm Muscles
0:23
So again, muscles of the forearm are what we’re gonna focus on.
0:26
And they’re divided into two main groups. We have the Anterior group, or the flexor muscles. We
0:32
have he Lateral group on the radial side, and we have the posterior group, the extensors. So let’s
0:38
work our way through all of the muscles here, starting with the anterior group.
Anterior (Flexor) Group
0:43
Alright. So here’s the anterior view of the forearm. The anterior group are divided into 4
0:49
layers. The 4th layer being closest to the bone, and the first layer being the most
0:54
superficial layer. The 1st layer consists of Palmaris Longus, Flexor Carpi Radialis,
0:59
Pronator Teres and Flexor Carpi Ulnaris. P F P F. The 2nd layer is the flexor
1:05
digitorum superficialis. The 3rd layer is the Flexor
1:08
Digitorum Profundus and Flexor Pollicis Longus. Ad the 4th layer is the Pronator Quadratus.
Pronator Quadratus
1:14
Now let’s start deep and then go superficially. Ok. So the Pronator Quadratus is located down
1:20
here. Doooown here, zooming in to see it better. It originates from the Anterior surface of Ulna
1:26
and Insert at the Anterior surface of Radius. Its function is pronation of
1:31
the forearm, so rotating the palm to the back. So, it’s a very small and straight forward muscle,
1:37
now let’s do the 3rd layer of the flexor group. The first one is the Flexor Digitorum Profundus.
Flexor Digitorum Profundus
1:43
Flexor digitorum profundus look like this. It’s easier to see its tendons if we highlight it.
1:49
It originates from the Anterior surface of Ulna, as you see here,
1:53
and insert at the base of the distal phalanges of the 2nd to 5th fibers, as you see here.
1:58
This muscle is responsible for flexion of the 2nd to 5th fingers at the metacarpophalangeal and the
2:05
interphalangeal joints, as well as accessory flexion of the hand. So that’s this muscle.
Flexor Pollicis Longus
2:11
Next, we have the Flexor Pollicis Longus, which is here.
2:14
It originates from the anterior surface of the Radius, and inset at the Base of the Distal
2:19
Phalanges of the thumb, or the first finger. And when the muscle fibers of this muscle
2:24
contract, they flex the thumb at the metacarpophalangeal
2:28
and the interphalangeal joints, as well as help with accessory flexion of the hand.
2:33
So that is the 3rd Layer. Next, we have the 2nd layer, which consist of the flexor digitorum
Flexor Digitorum Superficialis
2:38
superficialis. This large muscle here. This muscle originates from the Medial
2:43
epicondyle of the humerus, it originates from the Ulna and the Anterior surface of the radius.
2:49
Then it inserts at the Base of the middle phalanges of the 2nd to 5th fingers.
2:55
And when it contracts, it flexes the 2nd to 5th fiber at the metacarpophalangeal joints,
3:01
and the proximal interphalangeal joints. And it also helps with accessory flexion of the hand.
3:06
So that’s the 2nd layer. The 1st layer, which is the most superficial layer,
3:12
consist of these muscles you see here. These are the Pronator Teres,
1st Layer
3:16
Flexor Carpi Radialis, Palmaris Longus and Flexor Carpi Ulnaris. All of these muscles,
3:22
mainly, originate from the medial epicondyle of the humerus. Mainly. To keep it simple.
3:28
But they have different Insertion points and therefore some slight differences in function.
3:32
The first one, pronator Teres, inserts at the anterolateral surface of the Radius, around here,
3:38
and its function is in the name, it help pronating the arm by pulling the radius medially to rotate
3:44
the palm of the hand to the back. And it also helps flexing the lower arm as well.
3:49
Next the flexor carpi radialis, insert at the base of the 2nd to 3rd metacarpal bones,
3:55
down here. This muscle will flex the hand, as well as adduct the hand.
3:59
Next, we have the Palmaris Longus. The Palmaris longus insert at a structure
4:04
called Palmar Aponeurosis. The palmar aponeurosis is a fibrous triangle covering the palm to protect
4:11
the neurovascular structures underneath it. And it also fuses with the superficial palmar fascia
4:16
at some parts, we’ll talk about this one a little more when we cover the fascia of the upper limb.
4:21
Now the main function of the Palmaris Longus is to flex the hand. The last one is the Flexor Carpi
4:28
Ulnaris, which insert at medial structures of the wrist, like the Pisiform and Hamatum,
4:34
as well as the base of the 5th metacarpal bone. And the function of this muscle
4:38
is to flex the hand as well as adducting the hand. So that was all the muscles of the flexor group.
4:44
Next Let’s look at the lower arm from this perspective, so covert eh muscles of the radial
Lateral Group
4:48
side. The Radial muscles, or Lateral muscles, are grouped as Superficial layer and a Deep layer.
4:55
The superficial layer consists of the Brachioradialis, Extensor Carpi radialis
5:00
longus and Extensor Carpi radialis Brevis. The Deep layer consists of the Supinator. So
5:05
let’s do the deep layer first and then work our way from there. So,
5:09
the supinator look like this. It originates from the Lateral epicondyle of the Humerus,
5:14
Radial Collateral Ligament and the Ulna. And it inserts at the Lateral Surface of the Radius.
5:20
Its function is supination of the forearm, so rotating it like this.
5:26
Then we have the Superficial Layer, and our first muscle is the Brachioradialis muscle.
Brachioradialis
5:30
Which is here. It originates from the margin of the humerus, and insert at the radius,
5:36
above the styloid process as you see here. And the function of this muscle is alternating between
5:41
supination and pronation. It supinates on an extended forearm and pronates on a flexed forearm.
5:48
It also flexes the forearm, and fibers of this muscle stabilizes the elbow joint.
5:54
Aight. Next we have the Extensor Carpi Radialis Longus.
Extensor Carpi Radialis Longus
5:59
The extensor carpi radialis Longus originate rom the Lateral Margin and the Lateral Epicondyle of
6:05
the Humerus, and it inserts at the Base of the 2nd metacarpal bone, on the backside.
6:10
And when this muscle contracts, it abducts and extend the hand backwards.
6:15
That’s this one. Next we have the Externsor Carpi Radialis Brevis, which originates from the Lateral
Extensor Carpi Radialis Brevis
6:21
Epicondyle of humerus, and inserts at the Base of the 3rd Metacarpal Bone on the backside.
6:27
It has the same function as the extensor carpi radialis longus, which is abduction
6:32
of the hand, and extension of the hand. So that was the Lateral muscles of the lower arm.
6:38
Now let’s look at the forearm from this perspective, and covert eh extensor muscles.
Posterior Group
6:43
The extensors are also divided into Superficial and Deep layers. The superficial ones are the
6:49
Extensor Digitorum, Extensor Digiti Minimi, Extensor Carpi Ulnaris. And the Deep Layer
6:56
consist of Abductor Pollicis Longus. Extensor Pollicis Brevis and Longus. And Extensor Indicis.
7:03
Now let’s fill up the posterior forearm starting with the deepest muscles.
Abductor Pollicis Longus
7:08
The first one is the abductor pollicis Longus, which is this one. It originates
7:12
from the Posterior Surface of the Ulna and Radius, as well as the interosseous membrane between them.
7:19
It then inserts at the base of the 1st metacarpal bone.
7:22
And as the name says, it mainly abducts the thumb.
Extensor Pollicis Brevis
7:26
Next is the Extensor Pollicis Brevis, which is down here.
7:31
It originates from the Posterior surface of the Radius, as well as the interosseous
7:35
membrane. And it inserts at the base of the proximal phalanx of the Thumb
7:39
And when it contracts, it extends and abducts the thumb, this direction.
7:44
Then we have the long version of the extensor pollicis brevis, called extensor pollicis Longus,
Extensor Pollicis Longus
7:50
which is longer as you see here. It originates from the Posterior surface of Ulna this time
7:56
and the interosseous membrane. It then inserts at the distal phalanx of the thumb. Its function is
8:02
extension of the thumb, pulling it backwards. The last Deep layer muscle is the Extensor
Extensor Indicis
8:07
Indicis. Which is this one. It originates from the Posterior surface of Ulna and the
8:12
interosseous membrane, just like the extensor pollicis longus, and it inserts at the base
8:17
of the middle and distal phalanx of the index finger. Indicis means Index finger.
8:23
So its function is extension of the index finger, which is the 2nd finger.
8:28
So that was all the deep muscles of the posterior group of the forearm.
8:32
Now let’s cover the superficial layer. The first one is the Extensor
Extensor Digitorum
8:36
Digitorum muscle, which look like this. It originates from the Lateral Epicondyle of
8:41
Humerus, and it Inserts at the Base of the middle and Distal Phalanges of the 2nd to 5th fingers
8:49
The function of the Extensor Digitorum is to Abduct the fingers and also
8:54
extension of the hand, pulling it backwards. Then we have the Extensor Digiti Minimi, which
Extensor Digiti Minimi
9:00
is this one. Extensor Digiti minimi originate from the Lateral Epicondyle of the Humerus,
9:05
and then insert at the base of the middle and distal phalanges of the 5th finger
9:10
The name of the muscle is Extensor Digiti minimi, so the major function of this
9:16
muscle is extension of the little finger. Then we have the Extensor Carpi Ulnaris,
Extensor Carpi Ulnaris
9:21
which is this one. It originates from the Lateral Epicondyle of the Humerus, and the Posterior
9:26
Surface of Ulna, and it inserts at the Base of the 5th metacarpal bone, on the medial side.
9:32
And the function of this muscle is extension of the hand and adduction of the hand.
9:38
So that was all the muscles of the posterior group of the lower arm.
9:42
I know it’s a lot of muscles guys. But I promise once you go through them a couple of times, they
9:46
will get easier to visualize. In the next video, we’ll take a look at the muscles of the hand.