Final answer:
The extensor pollicis brevis is a muscle in the forearm that extends the thumb at the metacarpophalangeal joint. It is innervated by the posterior interosseous nerve and receives blood supply from the posterior interosseous artery.
Step-by-step explanation:
The extensor pollicis brevis is a muscle located in the deep posterior compartment of the forearm. It originates from the radius bone and inserts onto the base of the proximal phalanx of the thumb. It is responsible for extending the thumb at the metacarpophalangeal joint.
The extensor pollicis brevis is innervated by the posterior interosseous nerve, a branch of the radial nerve. It receives its blood supply from the posterior interosseous artery.
In summary, the insertion point of the extensor pollicis brevis is the base of the proximal phalanx of the thumb. Its action is to extend the thumb at the metacarpophalangeal joint. It is innervated by the posterior interosseous nerve and receives its blood supply from the posterior interosseous artery.