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Shoulder, Rib Cage and Upper Limb

The rib cage (or thoracic cage) is made up of 12 pairs of curved ribs (24 ribs). They are all attached in the back to the thoracic vertebrae. The top 7 pairs are called true ribs and are attached right to the sternum (or breastbone) in the front. The bottom 5 pairs are called false ribs. The top 3 false ribs are connected to the sternum in front only by a cartilage bridge. The bottom 2 ribs don't attach in front at all! They are called floating ribs. Ribs are considered flat bones.

The function of the ribcage is to protect the heart and lungs. It also anchors important muscles that work the lungs during breathing (respiration). The diaphragm and intercostals muscles attach to the ribcage drawing it up and out when we inhale. (Inhale and feel your ribcage rise and grow). This expands the lungs (which are also attached to the ribcage through a double lining called the pleura) and brings air into the lungs (inhale). When the muscles relax, the ribcage sinks and gets smaller again and we breathe out (exhale).

Skeletal System - Shoulder, Ribcage and Upper Limb

Each shoulder (pectoral girdle) really only has 2 bones, the clavicle and the scapula. The clavicle (collar bone) sits right over the 1st rib and attaches from the top of the sternum out to the scapula. If you run your fingers out from the front of your neck to your shoulder, you are running it along the clavicle on each side. The scapula, a flattened triangle of bone that lays on the back on the ribcage, forms the shallow dish where the head of each arm bone (humerus) sites.

This joint's job is arm movement. It is a ball and socket joint, which gives the arm a great range of motion, but it also is not as stable as a hinge joint (like the elbow) and can get injured (dislocated) more easily. The shoulder joint is kept together (stabilized) by muscles and tendons forming what is called the rotator cuff.

Skeletal System - Shoulder, Ribcage and Upper Limb

The upper limb includes the humerus (arm), the radius and ulna (forearm) and the bones of the hand: carpals (wrist), metacarpals (palm) and phalanges (fingers and thumb). The humerus is a long bone connected to a ball and socket joint in the shoulder and a hinge joint at the elbow. The radius is on the thumb-side of the forearm. The ulna is on the pinky side of the forearm and includes the elbow (olecranon process). The hand has 27 bones; 8 carpels in the wrist, 5 metcarpels in the palm and 14 phalanges (each finger has 3, except the thumb, which has 2.)

The arm and forearm bend at the elbow in a hinge joint, which is not as flexible as the shoulder joint, but is much more stable. The hand with its many joints is made to be flexible and agile. It can grasp and lift a heavy suitcase or careful pick up a pin. The upper limb is made to do both and everything in between.

Skeletal System - Shoulder, Ribcage and Upper Limb

The hand includes the carpals (wrist), metacarpals (palm) and phalanges (fingers and thumb). The hand has 27 bones; 8 carpels in the wrist, 5 metacarpels in the palm and 14 phalanges (each finger has 3, except the thumb, which has 2.)

The hand with its many joints is made to be flexible and agile. It can grasp and lift a heavy suitcase or careful pick up a pin. The upper limb is made to do both and everything in between.

Skeletal System - Shoulder, Ribcage and Upper Limb

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Next Generation Science Standards (NGSS)

Grade 6-8 - MS-LS1 From Molecules to Organisms: Structures and Processes

LS1.A: Structure and Function
• All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular). (MS-LS1-1)
• Within cells, special structures are responsible for particular functions, and the cell membrane forms the boundary that controls what enters and leaves the cell. (MS-LS1-2)
• In multicellular organisms, the body is a system of multiple interacting subsystems. These subsystems are groups of cells that work together to form tissues and organs that are specialized for particular body functions. (MS-LS1-3)

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