this is a tutorial on the muscles of the posterior compartment of the forearm so these muscles are extensor so it's also called the extensor compartment so hopefully you've watched the tutorial I did on the muscles of the anterior compartment so the muscles of the flexor compartment have a common origin on the medial epicondyles of the extensive compartment have a common origin on the lateral epical of the humorus so these muscles produce extension at the wrist joint extension extension of the fingers and thumb and superation of the forearm and all the muscles in the posterior compartment of forum are innovated by the radial nerve so in the posterior compartment you can separate the muscles into a superficial layer and a deep layer so first I'm going to talk about the muscles of the superficial lay and there are seven muscles in the superficial layer and the tendons as you can see here pass through this retinaculum which is called the extensor retinaculum and this is a fibrous um band of connective tissue which holds these tendons in place so I'll just remove that and we can take a look at these muscles now so there are seven muscles that you've got in The Superficial lay I'm just going to work lateral to medial so we're looking posteriorly at the um right arm here so this side is lateral so the most lateral muscle of the posterior compartment is this muscle here the bracho radialis muscle and this muscle as the name suggests originates on the arm so bracho brachium is Latin for arm so it originates on the humorus and it inserts onto the lateral surface on the distal radius so bracho radialis so it originates on the super condol Ridge the lateral super cond Ridge of the humus and it runs down the forearm and inserts laterally on the distal forearm on the distal radius sorry so that's the bracho radialis and what this muscle does is that it can act as an accessory flexor of the elbow so just working imly the the muscle just next to the bracho radi here which inserts slightly lower down on the suond ridge the lapal supercond ridge this is the extensor carpy radialis longus so this muscle originates on the a little bit below the brao radialis on the lateral super condol Ridge and it inserts down here on the um base of the second metacarpal so this is the dorsal surface on the base of the second metacarpal so what this muscle does is it extends the wrist and it also can abduct the wrist so when it contracts it pulls the wrist back this way and it can also pull the wrist up like this abducting it so medial to this muscle you've got the extensor carpy radialis brevis so we've got the longus here and the brevis here so brevis in Latin means short so you get the English derivative uh word um brevity meaning referring to shortness so brevis means short in Latin so it refers to the shortness of the tendon of this muscle so this muscle inserts originates on the um lateral epicondyles so this must muscle has the same action as the extensor kpy radialis longus in that it extends and abducts the wrist so medial to this muscle we've got the extensive digitorum which in which originates on the lateral epicondilite Cary radialis brevis and you can see this muscle here so this is the outline of the muscle and if we follow it down the forearm you can see it gives off four tendons so you've got these four tendons coming off the extensive digitorum and they run on the dorsum of the hand and insert onto the base of the middle sorry the middle and distal fance of these four digits so so the index middle ring and little fingers so I've just switched over to a diagram to show you this muscle so you've got this um the extented digital uh tendons here and you can see at the dorsum of the hand so over the metacarpal they actually interconnect but over the fanges um you can see how the tendon splits around itself so one part of the tendon inserts at the base of the middle fance and then it splits around to insert at the base of the distal fance so just to show you that a bit more clear so that's the extens of digitorum so remembering digitorum refers to the finger so it's extens of the fingers so this muscle extends the index middle ring and little fingers and it can also extend the wrist so just going back up to look at the next muscle so just quickly go recap so you've gone through the break bracho radialis the extent extensor carpy radialis longus the extensor carpy radialis brevis the extensor digitorum muscle and next we've got this muscle here the extensor digity minimi so this muscle lies medial to the extensor digitorum and as the name suggest it's the extensor of the smallest finger so minimi is Latin for smallest digity obviously finger so extends the little finger so again this muscle um originates on the lateral epicondyle again we've got the extensor carpy Alaris so this is the antagonist of the flexor carpy alarus which you can see just here with its alar and humal heads in the flexor compartment so this is the flexor carpy alar sorry extensor carpy Alaris and what this does is it extends and adducts the wrist so it originates here on the lateral epicondyle so you can see that there so you shouldn't get really too confused about whether um it adducts or abduct because if you know where it inserts you can imagine the muscle Contracting and try to visualize its action so you've got these two muscle you've got the extensor carpy Alaris and you've got the extensor kpy radialis and you've got the longest in brevis the because they insert on the radial side they're going to abduct the wrist because they insert on the radial side so away from the midline and they're going to pull pull it up this way abducting the wrist the extensor Cary alar inserts on the alna side so it's going to adduct the wrist so the final muscle um of The Superficial aay of the posterior compartment is this little muscle here the anconeus muscle so this muscle originates on the lateral epicard of the humus again and it inserts posteriorly on the alna and on the electron so there are seven muscles to remember here um so again you got the breako radialis you've got the extensor carpy radialis longus the extensor carpy radialis brevis you've got the extensor digitorum muscle the extensor digity minimi the extensor karpy Alaris and the anconeus muscle and these muscles form The Superficial layer okay so if I remove all these seven superficial muscles of the posterior compartment we can take a look at the um muscles of the deep deep layer of the posterior compartment so there are five muscles in the Deep layer of the posterior compartment of the forearm and these muscles um apart from the superator which has one head that attaches to the lateral epic condol these muscles all originate on the posterior surfaces disty on the alar and radius and the inter oous membrane so all these muscles all five of these muscles are innovated by the posterior interus nerve so this this nerve is a continuation of the deep branch of the radial nerve so first we've got this muscle up here the superator muscle so as this name suggests this muscle supernates the forearm and it has two heads it's got a superficial and a Deep head so it's got one head which attaches to the lateral epicondyle wraps around the lateral um edge of the radius on the shaft so just below the head and neck of the radius and it inserts laterally on the radius so this muscle supernates the forearm and there are two supernats of the forearm you've got the biceps as well so remember the bicep flexes the elbow and it also supernates the forearm so two supernats you've got so that's the most proximal muscle now just working our way a little bit more disly we've got this muscle here the abductor pocis longus so this muscle originates distill to the um superator and it originates on the posterior surfaces of the alner and the radius and also um it attaches to the interus membrane in between so winds down the forearm and it inserts here on the base of the first meta carple so what this muscle does when it contracts is that it abducts the carpo meta carpal joint so this joint between the carpal bones and the metacarpal so this thumb joint it abducts the thumb so the word pocis refers to thumb so in Latin po po pocis um means thumb so it's the abduct of the thumb so just distal to the abductor Pocus longus you've got this muscle here which is the extensor Pocus prev so this muscle originates on the posterior surface of the radius bone and it inserts on the dorsal surface of the base of the proximal FX so you've got the proximal and distal fance in the thumb and it inserts um at the base of the proximal fance here so when this muscle contracts it extends the metacarpo fenal joint so this joint here between the metacarpal and the phag so it it extends this joint and it can also extend the carpo metacarpal joint of the thumb so that's the extensor pocis previs so the next muscle is the extensor pois longus so it's this muscle here and this muscle um originates a bit higher up on the posterior surface of the AL bone so the the brevis muscle the brevis counterpart originated on the posterior surface of the radius the extensor Pocus longus originates on the posterior surface of the alab bone and then this muscle has a longer tendon so it's called longus so brevis means short in Latin longus means long obviously and this this muscle has a longer tendon so it inserts on the distal fance the base of the distal fance of the thumb of the um so here on the dorsal surface again so when this muscle contracts you can see that it will extend the interf Fallen gal joint of the thumb and again it can also extend the carpo carple and the metacarpo falang joints so this joint here and this joint here but it Prime purpose is to extend the interal jum joint of the thumb so that's the extensor Pocus longus because it's got a longer tendon which inserts more dist so finally we've got this muscle here which inserts originate sorry more distal to the um extensor pocis longus and it's called the extensor IND indicis so indicis in um refers to the index finger so it's um the extent of the index finger so this muscle originates on the posterior surface of the Elna distal to the extensor Pocus longus and then it inserts into the extensor hood of the index finger so do you remember that muscle I showed you in The Superficial the extensive digitorum which extends all four fingers well this muscle joins the insertion point of the extensive digitorium um to in to extend the index finger so there you have the um five muscles of the deep layer of the posterior compartment of the forarm so you've got the superator up here which supernates the forearm and then you've got the muscles of the thumb and the index finger so you've got the abductor pocis longus the extensor pocis brevis extensor pocis longus and the extensor indices so there's quite a lot of muscles in the extensor compartment but they're all logically named um so have a look through that through this tutorial again and hopefully that will help with things