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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.
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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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