The tricep muscle primarily affects the arm by extending the elbow joint and contributing to shoulder joint stability.
The triceps brachii, located on the posterior aspect of the upper arm, is a three-headed muscle (hence "tri-") responsible for straightening the arm at the elbow. Here's a breakdown of its effects:
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Elbow Extension: This is the primary function. When the tricep contracts, it pulls on the ulna bone in the forearm, straightening the elbow. This action is crucial for pushing, throwing, and many everyday activities.
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Shoulder Joint Stabilization (Long Head Only): The long head of the tricep has a unique attachment point – the scapula (shoulder blade). This connection means it also plays a role, albeit a smaller one, at the shoulder joint (glenohumeral joint). Specifically:
- Humeral Head Positioning: When the arm is adducted (close to the body), the long head of the tricep helps to keep the head of the humerus (upper arm bone) properly positioned within the glenoid cavity (the socket in the shoulder blade). This helps prevent dislocations.
- Minor Shoulder Extension and Adduction: The long head can also assist with extending and adducting the arm at the shoulder, although its contribution to these movements is less significant compared to other shoulder muscles like the deltoid or latissimus dorsi.
Here's a simplified table summarizing the tricep's actions:
| Tricep Action | Joint Affected | Head Involved | Description |
|---|---|---|---|
| Elbow Extension | Elbow | All Heads | Straightens the arm at the elbow. |
| Humeral Head Stabilization | Shoulder | Long Head | Helps keep the upper arm bone properly positioned in the shoulder socket. |
| Shoulder Extension (Minor) | Shoulder | Long Head | Weakly assists in moving the arm backward at the shoulder. |
| Shoulder Adduction (Minor) | Shoulder | Long Head | Weakly assists in bringing the arm closer to the body at the shoulder. |
In essence, the tricep is essential for extending the elbow, enabling pushing and straightening movements, and the long head provides additional stability to the shoulder joint, contributing to overall arm function.
