Final answer:
The triceps brachii long head originates from the infraglenoid tubercle of the scapula, inserts on the olecranon process of the ulna, and is innervated by the radial nerve.
Step-by-step explanation:
Triceps Brachii Long Head: Origin, Insertion, and Innervation
The triceps brachii is a key muscle in the human body known for its role in extending the forearm. Specifically, the long head of the triceps brachii has a distinct origin, insertion, and innervation that contribute to its function. The origin of the long head of the triceps brachii is the infraglenoid tubercle of the scapula. It inserts on the proximal end of the olecranon process of the ulna. Innervation of the long head, as well as the other heads of the triceps brachii, is provided by the radial nerve (C6, C7, and C8), enabling the muscle to perform arm and forearm movements efficiently.
This muscle is of particular importance not only because of its powerful action in forearm extension but also due to its involvement with the shoulder joint. Despite being a three-headed muscle, the triceps brachii's long head uniquely crosses the shoulder joint and contributes to arm movements, in contrast to the lateral and medial heads, which are more directly involved with movements at the elbow.