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locomotion
movement of the entire animal as a whole
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endoskeleton
- hard structures inside the body.
- made from cartilage and bone
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bone
- made up of cells in a hard extracellular matrix of calcium phosphate, with small amounts of calcium carbonate and protein fibers.
- meet at locations called articulations or joints, so they can swivel, hinge, or pivot.
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tendon
bands of tough, fibrous connective tissue.
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flexor
the muscle that swings two long bones in an arc toward each other
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extensor
the muscle that straightens bones out
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muscle fiber
- a long, thin muscle cell.
- muscle fibers contain many myofibrils
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sarcomere
- alternating light-dark units that repeat down the length of a myofibril.
- they shorten as the cell contracts and lengthen when the cell is relaxed.
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sliding-filament model
the theory that muscle movements are caused by two types of long filaments: thick filaments and thin filaments, that slide past one another during contraction.
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thin filaments
- composed of two coiled chains of the globular protein actin.
- one end of each thin filament is bound to a structure called the Z disk which forms the wall of the sarcomere.
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thick filaments
- composed of multiple strands of a long protein called myosin.
- anchored to the middle of the sarcomere.
- myosin is the site of active movement
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rigor mortis
- the state an animal enters when myosin and actin are locked together shortly after the animal dies
- because ATP is unavailable in dead tissue, it suggests that ATP is involved in getting myosin to release from actin
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Since ATP is always available in living muscles, how do our muscles ever stop contracting and relax?
- Thin filaments contain 2 proteins called tropomyosin and troponin.
- They work together to block the myosin binding sites on actin so that the thick and thin filaments can't slide past each other.
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What happens when an action potential from a motor neuron arrives at a muscle cell and initiates contraction?
- 1. Action potentials trigger the release of the neurotransmitter acetylcholine (ACh).
- 2. The action potentials sptread along the muscle fiber and into the interior of the fiber via the middle of the muscle cell membrane called T tubules.
- 3. Proteins in T tubules open Ca^2+ channels in sarcoplasmic reticulum.
- 4. Ca^2+ is released from sarcoplasmic reticulum and causes troponin and tropomyosin to move.
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Skeletal muscle
- consists of unbranched multinucleate cells that contain multiple nuclei
- also known as striated muscle
- function is to move skeleton
- attached to bones
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cardiac muscle
- contains branched cells whose ends are connected by intercalated discs
- intercalated discs - protein-lined openings called gap junctions provide a direct cytoplasmic connection between adjacent muscle cells
- 1 or 2 nuclei
- function is to pump blood
- located in heart
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smooth muscle
- unbranched, lacks myofibrils, organized into thin sheets.
- function is to move food, help regulate blood pressure, etc.
- located in intestines, arteries, other.
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