Triceps Brachii Muscle: Action, Origin & Insertion

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  • 0:03 Straight Arm Muscle
  • 0:40 Origin
  • 1:22 Insertion
  • 1:43 Action
  • 2:05 Lesson Summary
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Lesson Transcript
Instructor: Dan Washmuth

Dan has taught college Nutrition, Anatomy, Physiology, and Sports Nutrition courses and has a master's degree in Dietetics & Nutrition.

The triceps brachii is the large, three-headed muscle located at the back of the arm. Wondering why or how this muscle has three heads? Watch this lesson to find out!

Straight Arm Muscle

Have you ever tried to do a push-up? Do you know what muscle or muscles are used to perform one? Most people would guess the chest muscle, or pectoralis major, and they would be partly correct. Another very important muscle of the push-up is the triceps brachii.

The triceps brachii is the muscle that runs down the back of the humerus, which is the long bone of the upper arm, and ends at the top of the ulna, which is the long bone of the forearm. The triceps brachii gets its name because it contains three muscle heads, or points of origin. These include the medial head, the lateral head, and the long head.

Origin of the Triceps Brachii

Each of the three different heads of the triceps brachii muscle has a separate point of origin. The following chart describes them:

Head of Triceps Brachii Point of Origin
Medial head The medial head originates from the back surface of the humerus, just below the radial groove, a diagonal groove or depressed area that is located near the middle of the humerus. The radial nerve runs along this groove.
Lateral head The lateral head originates from the back surface of the humerus, just above the radial groove.
Long head The long head originates from the infraglenoid tubercle of the scapula. The glenoid cavity is a round, concave portion of the scapula where the head of the humerus meets with the scapula. The infraglenoid tubercle is a small, round prominence just below the glenoid cavity.

Insertion of the Triceps Brachii

Even though the triceps brachii has three separate muscle heads and three separate points of origin, this muscle only has a single point of insertion. The muscle fibers from all three heads converge together and insert onto the olecranon process, the round prominence at the back and top of the ulna. The olecranon process forms the pointed portion of the elbow joint.

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