As the name suggests, this muscle is an extensor at the wrist joint, and travels along the radial side of the arm, so will also abduct the hand at the wrist.
This muscle is quite long, starting on the lateral side of the humerus, and attaching to the base of the 2nd metacarpal.
Being an extensor contained in the forearm, it is innervated by the radial nerve.
It initially runs along with brachioradialis, but becomes mostly tendon early on, running between brachioradialis and extensor carpi radialis brevis.
Blood is supplied by the radial artery.