Bones and Muscles Essay
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 down, the knees are flexed. Flexion of the hip or shoulder moves the limb forward towards the anterior side of the body. 2) Extension: straitening and extending of the joint to increase the angle between two bones or body parts. When standing up, the knees are extended. Extension of the hip or shoulder moves the limb backward towards the posterior side of the body.
3) Abduction: Moving the body part away from the body. Abduction of the wrist is called radial deviation. Raising the arms laterally, to the sides, is an example of abduction. 4) Adduction: moving the body part toward the midline of the body. Dropping the arms to the sides, or bringing the knees together, are examples of adduction. In the case of the fingers or toes, adduction is closing the digits together. Adduction of the wrist is called ulnar deviation. 5) Rotation: Moving the body part around its axis.
6) Internal rotation: Moving of shoulder or hip would point the toes or the flexed forearm inwards towards the midline.
7) External rotation: Moving would turn the toes or the flexed forearm outwards away from the midline.
8) Supination: Turning the palm of the hand upward.
9) Pronation: Turning the palm of the hand outward.
10) Eversion: Turning the body part outward.
11) Inversion: turning the body part inward.
12) Planter flexion: Bending of the foot that causes the toe to point downward, as if pressing an automobile pedal.
14) Dorsiflexion: Bending of the foot that causes the toe to point upward.
15) Circumduction:The circular (or, more precisely, conical) movement of a body part, such as a ball-and-socket joint or the eye. It consists of a combination of flexion, extension, adduction, and abduction. “Windmilling” the arms or rotating the hand from the wrist are examples of circumductive movement.
16) Opposition: A motion involving a grasping motion of the thumb and fingers.
17) Reposition: To release an object by spreading the fingers and thumb.
~Structures of the Muscle that Allows Movement~
The contractile apparatus in each muscle fibre is arranged in parallel long cylindrical strands, called myofibrils. Actin and myosin are the contractile protein polymers contained in myofibrils and they too are long and lie parallel and lengthways. Using energy derived from ATP, the actin and myosin “filaments” attach via cross bridges and slide past each other in opposite directions, thus causing a contraction.
Just like an oar in a rowing boat, it reaches out from the myosin filament (or rowing boat) and grabs on to the actin (or water), and pulls the actin towards it and then pushes it away. The cross-bridge oar is then recycled so it can grab on to another bit of actin (water) and so continue the contraction. This is the “sliding filament’ and cross-bridge theories which explains how muscles shorten.
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