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Chapter 12 Notes - Muscles

Chapter 12 Notes - Muscles - Muscles have two common...

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Muscles have two common functions: to generate motion and to generate force. Skeletal muscles also generate heat and contribute significantly to the homeostasis of body temperature. - Attached to the bones of the skeleton - Control body movement - Striated - Contract only in response to a signal from a somatic motor neuron (cannot initiate their own contraction, nor can they be influenced by hormones). Cardiac muscle – responsible for moving blood through the circulatory system. - Striated Smooth muscle – primary muscle of internal organs and tubes (stomach, urinary bladder, blood vessels) - Moves materials into, out of, and within the body. Skeletal Muscle Understand flexion and extension - Flexor/extensor pairs are antagonistic muscle groups because they exert opposite effects. Sarcolemma is the cell membrane of a muscle fiber Sarcoplasm is the cytoplasm of a muscle fiber - Contains many glycogen granules (reserve source of energy) and mitochondria (provide the needed ATP for muscle contraction). Myofibrils – highly organized bundles of contractile and elastic proteins that carry out the work of contraction. Sarcoplasmic reticulum – wraps around each myofibril; releases calcium ions and also sequesters them. T-tubules – closely associated with the terminal cisternae (part of the SR that sequesters the calcium ions) - Rapidly move action potentials that originate at the neuromuscular junction on the cell surface into the interior of the fiber. - Without t-tubules, action potentials reach the center of the muscle fiber by diffusion of positive charge through the cytosol (too slow) Myosin – motor protein of the myofibril - Join together to create thick filaments. Actin – make up thin filaments
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Thick and thin filaments are joined together by crossbridges that span the space between the filaments. A sarcomere is a repeating pattern of alternating light and dark bands seen in skeletal muscle - Z-disks – two found in a sarcomere (attachment site for thin filaments) - I-band – region occupied by thin filaments. A Z-disk runs through the middle of every I band, so each half of an I band belongs to a different sarcomere. - A - band – encompasses the entire length of a thick filament. At the outer edges, thin and thick filaments overlap. - H - zone – occupied by thick filaments only - M-line – form the attachment site for thick filaments ( equivalent to the Z-disk for thin filaments) Proper alignment of filaments within a sarcomere is ensured by titin and nebulin Titin stretches from one Z disk to the neighboring M line - Stabilizes the position of myosin. - Returns stretched muscles to their resting length. Nebulin – helps align the actin filaments in a sarcomere Contraction – creation of tension in a muscle. It’s an active process Relaxation – release of tension created by a contraction.
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