Okay so this a tutorial on the muscles of the flexor compartment of the forearm.
So just like the upper arm, the muscles of the forearm can be split into anterior and
posterior compartments - so flexor and extensor compartments.
So the flexor compartment is separated from the extensor compartment by bones, an interosseus
membrane and a lateral intermuscular septum.
So here I'm just showing you a cross section of the forearm, so this is anterior, posterior,
lateral and medial, and you've got the ulna and radius we are looking at.
So in between the radius and ulna, you've got this membrane called the interosseus membrane.
So "inter" meaning "between", "os" Latin for "bone", so "between the bone membrane" - "inter-osseous
membrane".
Connecting to the radius you've got the lateral intermuscular septum, which connects to the
deep fascia, which surrounds the muscles of the forearm.
So you've got these compartments, the anterior flexor compartment, and the posterior extensor
compartment.
So this interosseus membrane runs between the radius and ulna in this gap here, separating
the anterior and posterior compartments.
So the anterior compartment, the flexor compartment, which I'm talking about in this tutorial,
the muscles are generally supplied by the median nerve, and these muscles have a common
origin on the medial epicondyle of the humerus.
So this part here.
And if these muscles are overused, then you can get inflammation at this origin, so you
get medial epicondylitis which is also known as "golfers elbow".
So the muscles of the anterior compartment flex the wrist and digits, and pronate the
hand.
So pronation is bringing the hand round so that the palm faces away from you, sorry towards
you.
So in this position here, in the anatomical position, the palm is facing away from you,
so pronation would bring the palm to face towards you, so that you show the back of
the hand, so it would rotate the hand around.
So the muscles of the posterior compartment do the opposite to the anterior compartment
muscles - they extend the wrist and digits, and they supinate the hands, and they have
a common origin on the lateral epicondyle of the humerus.
So overuse of the posterior compartment, the extensors of the forearm, you get lateral
epicondylitis, which is also known as tennis elbow.
So you've got three layers of muscle in the anterior forearm, you've got the superficial
layer, the intermediate layer, and the deep layer.
So I'm just going to talk you through from superficial to deep, these muscles.
So in the superficial layer you've got four muscles, you've got the flexor carpi ulnaris,
the palmaris longus, the flexor carpi radialis, and the pronator teres.
So I'll just start with this muscle here, which is the pronator, sorry, the palmaris
longus, so this muscle like the rest of the muscles of the anterior compartment, it originates
on the medial epicondyle of the humerus and it runs down the length of the forearm to
insert onto this flat fibrous sheath, known as the palmar aponeurosis, so this is a thick
layer of deep fascia that lies beneath the skin.
So you can see this tendon in yourself, if you flex your wrist, it's quite superficial,
you can see that tendon.
So what this muscle does, the palmaris longus is that it flexes the wrist joint.
So this palmar aponeurosis actually attaches to the overlying skin of the palm and the
fingers.
So when you contract the palmaris longus, it flexes the wrist.
So medial to the palmaris longus, you've got this muscle called the flexor carpi ulnaris.
So it's useful to try and think of what the words actually mean, so flexor obviously means
it flexes, causes a flexing action at the wrist, carpi is Latin, "carpus" means wrist,
and ulnaris refers to the ulna side.
So it flexes the wrist at the ulna side.
So this muscle actually has two heads, so I'll just rotate this model round, and you
can see one head inserting on the medial epicondyle of the humerus, and the other head inserting
posteriorly on the ulna and at the olecranon - so its got two heads, the flexor carpi ulnaris.¬¬
So what this muscle does is it runs down and inserts at the wrist, down here.
So it actually, it's not very clear on here, but it inserts on this little bone here - the
pisiform bone, and this bone has ligaments which attach to this metacarpal, so this fifth
metacarpal bone.
So it inserts on this little bone here and this pisiform bone, which I'll talk about
in another tutorial, has ligaments which attach onto this fifth metacarpal, so what this muscle
does when it contracts, is that it flexes the wrist and adducts the wrist.
So just lateral to the palmaris longus, which I just talked about, so this muscle here which
attaches to the palmar aponeurosis, you've got the flexor carpi radialis.
So remember what I just said about the word "carpi" meaning "wrist", and looking at the
name of the muscle to get an idea of its function and its structure.
So flexor - flexes, at the wrist - carpi, on the radial side.
So, you can see here it inserts at the medial epicondyle of the humerus, sorry, originates
there, and it runs down the forearm to insert onto the metacarpals.
So I'll just remove the palmar aponeurosis, and you can see that it has this insertion
point at the base, so you've got these metacarpals here and these phalanges, so these are the
metacarpals, so it inserts onto the base of the second and third metacarpal.
And when this muscle contracts, it flexes and adducts the wrist, sorry abducts - AB-ducts.
So the fourth and final muscle in the superficial layer is this muscle, which lies lateral to
the flexor carpi radialis, it's the pronator teres.
So as the name suggests it pronates the forearm.
So...two origins, two origins, it originates on the medial epicondyle of the humerus and
also on the ulna bone, and it inserts onto the lateral part of the mid-shaft of the radius.
So when this muscle contracts, it pronates the forearm.
So you've got those four muscles of the superficial layer of the anterior compartment.
You've got the flexor carpi radialis, and ulnaris, which lie either side of the palmaris
longus, and then you've got the pronator teres which lies lateral.
Okay so now I'm just going to dissect away the superficial muscles and we'll look at
the intermediate muscle layer, so there's one muscle in the intermediate muscle layer
- the flexor digitorum superficialis, so the name gives you some idea of its function.
So obviously it's a flexor muscle, because it's in the anterior compartment, so the word
digitorum refers to fingers, so it flexes the fingers.
And it's called superficialis, because it's superficial to the other muscle which acts
to flex the fingers, which I'll show you in a moment.
So the flexor digitorum superficialis lies in the intermediate muscle layer, of the anterior
forearm, and it has two origins: it's got this humero ulna origin, and it's got this
other origin on the radius bone.
I'll just get rid of that quickly.
So it originates on the medial epicondyle of the humerus also on the ulna and it also
originates on this radial, this oblique line on the radius.
It then runs down and you've got these four tendons which pass through the carpal tunnel,
so the carpel tunnel is this space between the flexor retinaculum and the carpal bones,
and the median nerve passes through this, and when it, when the contents of the carpal
tunnel get compressed, you get muscle weakness and loss of sensation, and I'll talk a bit
about that in another tutorial.
So you've got these four tendons of the flexor digitorum superficialis which run through
the...underneath the flexor retinaculum, and they insert onto the middle phalanx of the
index, middle, ring and little fingers.
So this tendon is quite interesting because it actually split and inserts onto the lateral
margins of the middle phalanx, and it allows this other tendon to pass through, so the
tendon of the flexor digitorum profundus, to pass through.
So the tendons of the flexor digitorum superficialis insert onto the middle phalanx, so they split
to allow the passage of this flexor digitorum profundus.
So an easy way of remembering this, is that "superficialis splits; profundus passes through",
so "s" - superficialis splits, so beginning of the word begins with "s" so "superficial
splits; profundus passes through".
So it inserts on the lateral margins of the middle phalanx.
So just to orientate you a bit, you've got the metacarpal bones here, you've got the
proximal phalanx, middle phalanx, and distal phalanx.
So you've got your proximal interphalangeal joint, and your distal interphalangeal joint.
So the action of the flexor digitorum superficialis is to flex at the proximal interphalangeal
joint, of the index, middle, ring and little fingers, and it can also flex at this joint,
so the metacarpophalangeal joints.
So it can flex at the MCP joints and the PIP joints of the index to little fingers.
So I'm just going to move onto the next muscle layer, the deep muscle layer.
Okay so I've rid of the flexor digitorum superficialis, and now we're looking at the flexor digitorum
profundus, so this muscle lies underneath the flexor digitorum superficialis, and it
originates on the anterior and medial surfaces of the ulna bone, and it runs down, and again
you've got these four tendons, which pass through the carpal tunnel, underneath the
flexor retinaculum, and they run along to insert onto the base of the distal phalanges.
So, I'll just bring back those other tendons, so you can see how they split, you can see
the tendon of the flexor digitorum superficialis splitting and the tendon of the flexor digitorum
profundus passing through to insert onto the distal phalanx.
So you can probably guess that this muscle, when it contracts, it flexes the distal interphalangeal
joint.
So the flexor digitorum superficialis flexes the proximal interphalangeal joint, and the
flexor digitorum profundus flexes the distal interphalangeal joint.
And it can also flex the metacarpophalangeal joints, so the MCP joints.
Just bring you back up here.
So the next muscle is the flexor pollicis longus, so it's this muscle here, which is
actually shown a little out of place on this model, because it inserts more medially and
anteriorly on the radius bone, so more in this sort of region, so this is the flexor
pollicis longus.
So pollicis refers to the thumb, so we'll go through a lot of other muscles which act
on the thumb, and they all have the words "pollicis, so "pollicis" is Latin, referring
to thumb.
So what this muscle does is it flexes the thumb and the interphalangeal joint, so it
runs down.
Again it's shown a bit out of place, it actually runs underneath the flexor retinaculum in
the carpal tunnel, so it runs through the carpal tunnel and it inserts on the distal
phalanx.
So when it contracts it flexes the thumb at this interphalangeal joint, and it can also
flex at the metacarpophalangeal joint.
So the final muscle of the deep layer is the pronator quadratus, which lies underneath
the tendons of the flexor pollicis longus and the tendons of the flexor digitorum profundus.
So, from its rectangular shape, so "quadratus" referring to its four sides, so I've just
removed the flexor pollicis longus and the flexor digitorum profundus, and you've got
this pronator quadratus, so as the name suggests it's a pronator muscle, so it pronates the
wrist, and it's shown a bit funny here, but I'll just isolate it.
So it's actually this rectangular shape.
So it originates on this distal anterior surface of the ulnar, and it inserts distally on the
anterior surface of the radius, and it contracts, when it contracts, it pronates the forearm.
So those are the muscles of the anterior compartment, the flexor compartment of the forearm.
You've got the superficial, intermediate and deep layers, and you've got muscles which
flex the wrist, which flex the fingers, and which pronate the forearm.