Triceps brachii muscle Facts for Kids

The triceps brachii muscle is a muscle found on the back of your upper arm. It has three main parts that start from different places near your shoulder and join together at your elbow. This muscle helps you straighten your arm. Its name comes from Latin and means "three-headed muscle in the arm."

How the Triceps is Built
- How Nerves Control the Triceps
What the Triceps Does
Training Your Triceps
The Name "Triceps"
Triceps in Animals
Images for kids
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How the Triceps is Built

The triceps brachii has three main parts, often called heads. These are the long head, the medial (inner) head, and the lateral (outer) head.

The long head starts from your shoulder blade. It runs down your arm, passing between two other muscles called the teres minor and teres major.

A view inside the upper arm. The triceps muscle is shown with green writing.

The medial and lateral heads start from your humerus (your upper arm bone).

The medial head mostly has small, slow muscle fibers. These are good for careful, steady movements. The lateral head has larger, fast fibers. These are used when you need a lot of strength quickly. The long head has a mix of both types of fibers. Some scientists even think these three parts act like separate muscles!

All three parts of the triceps join together into a single strong cord called a tendon. This tendon attaches to the ulna bone in your forearm, near your elbow. Some studies suggest there might be more than one tendon.

How Nerves Control the Triceps

Scientists used to think that all three parts of the triceps got their signals from the radial nerve. This nerve sends messages from your brain to your muscles, telling them what to do. However, a study looked at 20 bodies and 15 living people. They found that the long head of the triceps actually got its nerve signals from a different nerve, called the axillary nerve, every time.

What the Triceps Does

The triceps muscle's main job is to straighten your elbow. It works against the biceps and brachialis muscles, which bend your arm.

The triceps also helps keep your elbow steady. This is important when you use your forearm and hand for small, careful movements, like writing or drawing.

The long head of the triceps might be used when you need to keep the same amount of force for a long time. It also helps control how your shoulder and elbow move. The lateral head is used when you need a lot of strength all at once. The medial part is used for more precise and careful movements.

The long head also helps move your shoulder joint. It can pull your arm backward or inward.

Training Your Triceps

A person training their triceps muscle.

You can train your triceps by itself or with other muscles. Any exercise that involves straightening your elbow or keeping it straight while holding something will work your triceps. For example, pushing movements like push-ups or overhead presses help strengthen this muscle.

The Name "Triceps"

The name "triceps brachii" comes from Latin and means "three-headed." It's called this because, as you learned, the muscle has three main parts or heads. Most people just call it the "triceps."

In the past, the plural of triceps was tricipites. But now, people usually say triceps whether they are talking about one muscle or many.

Triceps in Animals

In animals like horses, the long head of the triceps is very large. It makes up about 84% of the triceps' total weight. The lateral head is about 15%, and the medial head is about 3%.

Many other mammals, such as dogs, cows, and pigs, actually have a fourth triceps head! This extra part is called the accessory head. It is located between the lateral and medial heads.