| A | B |
|---|
| Skeletal muscle contractions really begin in the ___. | Motor neuron (nervous system) |
| When the nerve impulse reaches the skeletal muscle neuromuscular junction, this results in the release of ____ by exocytosis. | Acetylcholine from synaptic vesicles |
| Acetylcholine receptors of skeletal muscle are found in the ___. | Motor end plate |
| Binding of acetylcholine to receptors causes the sarcolemma to briefly become highly permeable to ___ ions. | Na + |
| As Na+ ions enter the skeletal muscle cell, this causes the net charge inside the cell to change from ____ to ____. | Negative to positive |
| When the charge inside a muscle cell becomes positive, this can be described as generating a muscle ___ potential. | Action |
| As a result of a muscle action potential, ___ ions leave the ____ through passive channels. | Calcium / SR |
| As the calcium level in the sarcoplasm rises, calcium binds to ___. | Troponin |
| As a result of having calcium bound to it, ___ changes shape and pulls ____ off the myosin binding sites. | Troponin / tropomyosin |
| In a relaxed skeletal muscle, myosin binding sites are covered by the regulatory protein ___. | Tropomyosin |
| Myosin binding sites are located on ___. | Actin (thin filaments) |
| Energy for contraction is produced by the breakdown of ___. | ATP |
| The enzyme ____, associated with myosin heads, breaks down ATP in skeletal muscle. | ATPase |
| With ATP energy and uncovered mysoin binding sites, ____ filaments grasp ___ filaments and pull them toward the center of the sarcomere. | Thicks grasp thins |
| Each little pull of thin filaments toward the center of the sarcomere is called a ____ stroke. | Power |
| A single nerve impulse in skeletal muscle would result in a very short contraction because _____ is quickly destroyed by an enzyme. | Acetylcholine |
| Acetylcholinesterase is found in the ____. | Synaptic celft |
| With no acetylcholine bound to receptors, the muscle sarcolemma becomes impermeable to Na+ and the extra Na+ is quickly pumped ____ of the cell. | Out |
| When the extra ___ is pumped out of the cell, the action potential is over. | Na+ |
| As the action potential ends, the calcium ions are put back into the SR by: | Active transport pumps |
| When calcium levels in the sarcoplasm drop, this results in covering of the ____. | Myosin binding sites |
| Active tension is generated by: | Thick and thin filaments (contractile elements) |
| Passive tension results from: | Slight stretch and recoil of elastic elements associated with muscle such as tendons and titin filaments. |
| A muscle contraction that results in shortening of the muscle and movement is ____. | Isotonic |
| A muscle contraction that increases tension but does not result in movement or shortening of the muscle is ___. | Isometric |
| In an isotonic contraction, the phase in which the muscle is shortening is the ___ phase. | Concentric |
| In an isotonic contraction, the phase in which the muscle gradually lengthens is the ___ phase. | Eccentric |
| Wasting away of muscle is muscular ___. | Atrophy |
| If a muscle completely loses its nerve supply, the result is wasting and finally loss of ________ due to ____ atrophy. | Muscle cells / denervation |
| When an arm or leg is in a cast and its muscles temporarily shrink, this is ___ atrophy and is reversible. | Disuse |
| When muscles get larger, this is muscular ___. | Hypertrophy |
| When a muscle enlarges, _____ increase but the number of muscle ____ remains the same. | Internal components such as mitochondria, myofibrils, and SR increase / cells (fibers) |
