Bones and Muscles

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~Cross-section of a bone~

Articular cartilage - is a white, smooth tissue which covers the ends of bones in joints.

Periosteum - is a fibrous sheath that covers bones. It contains the blood vessels and nerves that provide nourishment and sensation to the bone.

Cortical bone - forms the outer shell of all bone and also the shafts in long bones.

Trabecular bone - is the tissue that makes up the interior of bones.

Epiphyseal plate - is an area at the long end of the bone which contains growing bone. 

Marrow - is the soft spongy tissue that lies within the hollow interior of long bones. 

Medullary cavity - is the cavity within a bone where a soft and flexible substance called marrow is stored.

~Osteogenesis: Development of the Bones~

In endochondral ossification bone tissue replaces hyaline cartilage, forming all bones below the skull except for the clavicles.

(1) Osteoblasts secrete osteoid, creating a bone collar around the diaphysis of the hyaline cartilage model. (2) Cartilage in the center of the diaphysis calcifies and deteriorates, forming cavities. (3) The periosteal bud invades the internal cavities and spongy bone forms around the remaining fragments of hyaline cartilage. (4) The diaphysis elongates as the cartilage in the epiphyses continues to lengthen and a medullary cavity forms through the action of osteoclasts within the center of the diaphysis. (5) The epiphyses ossify shortly after birth through the development of secondary ossification centers.

Intramembranous ossification forms membrane bone from fibrous connective tissue membranes, and results in the cranial bones and clavicles.

~Movements of Muscle~
1) Flexion: bending a joint to decrease the angle between two bones or two body parts. Bending the elbow, or clenching a hand into a fist, are examples of flexion. When sitting...
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