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| 31. | graded muscle response | modification of contraction strength |
| 32. | hyperplasia | process in which one cell splits to produce new cells |
| 33. | hypertonia | abnormally high muscle tone |
| 34. | hypertrophy | addition of structural proteins to muscle fibers |
| 35. | hypotonia | abnormally low muscle tone caused by the absence of low-level contractions |
| 36. | intercalated disc | part of the sarcolemma that connects cardiac tissue, and contains gap junctions and desmosomes |
| 37. | isometric contraction | muscle contraction that occurs with no change in muscle length |
| 38. | isotonic contraction | muscle contraction that involves changes in muscle length |
| 39. | lactic acid | product of anaerobic glycolysis |
| 40. | latch-bridges | subset of a cross-bridge in which actin and myosin remain locked together |
| 41. | latent period | the time when a twitch does not produce contraction |
| 42. | motor end-plate | sarcolemma of muscle fiber at the neuromuscular junction, with receptors for the neurotransmitter acetylcholine |
| 43. | motor unit | motor neuron and the group of muscle fibers it innervates |
| 44. | muscle tension | force generated by the contraction of the muscle; tension generated during isotonic contractions and isometric contractions |
| 45. | muscle tone | low levels of muscle contraction that occur when a muscle is not producing movement |
| 46. | myoblast | muscle-forming stem cell |
| 47. | myofibril | long, cylindrical organelle that runs parallel within the muscle fiber and contains the sarcomeres |
| 48. | myogram | instrument used to measure twitch tension |
| 49. | myosin | protein that makes up most of the thick cylindrical myofilament within a sarcomere muscle fiber |
| 50. | myotube | fusion of many myoblast cells |
| 51. | neuromuscular junction (NMJ) | synapse between the axon terminal of a motor neuron and the section of the membrane of a muscle fiber with receptors for the acetylcholine released by the terminal |
| 52. | neurotransmitter | signaling chemical released by nerve terminals that bind to and activate receptors on target cells |
| 53. | oxygen debt | amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction |
| 54. | pacesetter cell | cell that triggers action potentials in smooth muscle |
| 55. | pericyte | stem cell that regenerates smooth muscle cells |
| 56. | perimysium | connective tissue that bundles skeletal muscle fibers into fascicles within a skeletal muscle |
| 57. | power stroke | action of myosin pulling actin inward (toward the M line) |
| 58. | pyruvic acid | product of glycolysis that can be used in aerobic respiration or converted to lactic acid |
| 59. | recruitment | increase in the number of motor units involved in contraction |
| 60. | relaxation phase | period after twitch contraction when tension decreases |
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