the triceps muscle is the large fusiform muscle which forms the posterior compartment of the arm the triceps muscle is by articular as it crosses both the shoulder joint and to the elbow joint acting as an extensor at each joint with the major action being at the elbow joint as suggested by its name the triceps has three heads and typically
has twice the size of your biceps muscle making up two-thirds of the muscle bulk within your upper arm the origins of the individual muscle heads in turn the long head of the triceps brachii originates from the infer glenoid cubicle this is a small bump found at the base of the glenoid fossa of the scapula the lateral head originates from the posterior surface of
the humerus superior to the radial groove the radial groove also known as the spiral groove is this groove on the posterior lateral surface of the humerus where the deep branch of the brachial artery and the radial nerve run the medial head lies deep to the other heads and originates from the posterior surface of the humerus inferior to the radial groove in terms of its insertion distally the heads of the triceps brachii converge onto a common tendon
which attaches to the proximal end of the electron of the ulna and blends with the fascia of the proximal forearm the triceps muscle is innervated by the radial nerve which is the terminal continuation of the posterior cord of the brachial plexus arising from spinal roots e6 to c8 it is worth noting that it's been shown that in some individuals
the long head of the triceps brachii is innervated by the axillary nerve the triceps muscle derives its blood supply from the profunda brachii artery which is the deep branch of the brachial artery this vessel passes posterior to the humerus within the radial groove and between the medial and lateral heads of the triceps the main function of the triceps muscle is extension of the forearm at the elbow joint because the long head crosses the shoulder joint the triceps muscle actually has a small role in shoulder extension and shoulder adduction although there are other muscles which are more important in these movements for example the latissimus dorsi and posterior fibers of the deltoid for extension and the pectoralis major and latissimus dorsi for adduction in addition the long head of the triceps has a role in stabilizing the abducted humerus at the shoulder joint by helping to resist inferior displacement of thehumeral head the medial head of the triceps seems to be the muscle most involved with forearm extension and it'sbelieved to be involved at all ranges of motion and both with and without resistance the lateral head is thought to be the strongest head but in contrast to the medial head it is recruited into activity against resistance in terms of clinically relevant points
it's important to note that the radial nerve which supplies the triceps muscle can be injured with humeral fractures dependin on the location of the fracture this may weaken but not completely paralyzed the triceps muscles because the nerve branches innovating the lateral and long heads arise superior to the radial groove a more distal fracture at the mid shaft may therefore cause partial weakness whereas a proximal injury may paralyze all of the three heads of the triceps
