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24 September 2014
Human Body & MindScience & Nature

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Skeleton - Arm and shoulder

Shoulder socket: Is made by your collarbone and shoulder blade

Ulna: You often rest your ulna on the table

Shoulder

Your shoulder is made up of a collarbone (clavicle) and a shoulder blade (scapula). These bones project out from your body forming a scaffold for your arm to hang from.

Your collarbone is a thin bone that bridges the top of your sternum, in the front of your ribcage, to your shoulder socket at the end of your shoulder blade. It is the only bone in your shoulder that connects directly to your ribcage. Your collarbone supports the weight of your entire arm. When someone has a broken shoulder, they usually hae damaged their collarbone. If the bone has snapped completely, the whole shoulder sags.

Your shoulder blade is a large flat bone. It's not connected to your ribcage, but is held in place by your shoulder muscles.

The ends of your collarbone and shoulder blade meet, forming a shoulder socket that your arm fits into. This 'ball and socket' joint is loosely held in place by ligaments. This makes your shoulder joint incredibly flexible, but means it can be dislocated more easily than other joints in your body.

Arm

Your arm is made up of three long bones: your humerus in your upper arm and your ulna and radius in your lower arm. Your upper and lower arms are connected at your elbow by a hinge joint between your humerus and ulna. Your radius and ulna are linked at your elbow in a way that allows you to rotate your hand and forearm by more than 180 degrees. Your ulna bone forms the point of your elbow.

Your shoulder and arm bones have roughened patches on their surfaces where muscles are attached. When the muscles contract, this pulls the bone the muscles are attached to, making your arm move.

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