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BIO 281 - Muscles 3
Stack #128824
| Question | Answer |
|---|---|
| Single muscle twitch | single, rapid muscle contraction in response to a threshold stimulus |
| Myogram | machine that measures contractile activity |
| 3 distinct phases of single muscle contraction | latent period, contraction, relaxation |
| Latent period | no measureable increase in tension, "signal," gen. AP releasing Calcium from SR, etc. (~2 msec.) |
| Contraction | Onset of shortening to max. tension developed; crossbridge form, swivel, detach (10-100 msec.) |
| Relaxation | stop generating contractile force... tension decreases (10-100 msec.) Calcium is pumped out of cell, tropomin + tropamysin, block crossbridges... |
| Single muscle twitch response is | "all or none" |
| Response | in response to appropriate stimuli, skeletal muscle contracts maximally or not at all |
| Responses to stimuli | subthreshold; threshold; suprathreshold |
| Subthreshold | no appropriate stimuli |
| Threshold | appropriate stimuli |
| Suprathreshold | above appropriate stimuli |
| Summation of contraction (aka Temporal or Wave Summation) | accumulation of effects; "add together" - Tetanus - Treppe |
| Accumulation of effects; "add together" (relaxation) | mechanical structures of muscle fibers don't need relaxation before another contraction; 2nd contraction can be started before thick and thin filaments back to resting; 2nd contraction has "head start" in shortening; gets shorter than 1st contraction |
| Accumulation of effects; "add together" (frequency) | as AP frequency increases, frequency of contractions increases, until level off at maximum tension |
| Tetanus | smooth sustained muscle contraction, no relaxation... lots of stimuli, fast; the AP refractory period is still there, but "machinary" doesn't rest; Calcium stays in sarcoplasm until signal ends or runs out of ATP |
| Tetanus (cont.) | incomplete vs. complete |
| Treppe | "staircase" increase in muscle tension (single twitch) with successive stimuli; seems to be result of increase of Calcium in sarcoplasm or increase temperature (faster enzyme activity) ATPase |
| Recruitment (aka Multiple motor unit summation) | whole muscle organ is made up of many motor units |
| Motor unit | a single motor neuron and all the myofibers it innervates (stimulates) (communication) |
| Motor unit (cont.) | the number of fibers may vary; lots of fibers = large muscle with "strong" response; few fibers = small muscle with "fine" response; entire unit responds to stimuli in "all or none" fashion |
| Recruitment | threshold for action potentials may vary slightly between motor units; as signals gets stronger, add more/ stim. move motor units until recruitment |
| Movements "smooth" because | motor units contract out of phase don't notice single muscle twitches |
| Muscle tone | resting tension in a skeletal muscle |
| Muscle tone - movement | no movement but muscles "tense" and "firm" (not soft or flaccid) |
| Muscle tone - "relaxed" | "relaxed" muscles are almost always in slightly contracted state due to spinal reflexes - motor neurons stimulate muscles |
| Muscle tone keeps | muscles firm, healthy, and ready to respond - also helps with joint stabilization |
| Length-tension relationship | Initial length of sarcomere has a big effect on the amount of tension it can produce |
| Sarcomere | can generate most tension when thick and thin are slightly overlapped (contracted or relaxed) |
| Length-tension relationship - optimal | range 80-120% of normal resting length |
| Active tension | force generated by thick and thin filaments |
| Passive tension | tension generated by series elastic element (elastic filaments, perimysium, endomysium, tendons) depends on the degree of stretch |
| Isotonic contraction | tension increases to overcome resistance then length of muscle decreases and tension stays the same |
| Isometric contraction | load to heavy tension does not exceed resistance so muscle can't shorten length stays same |
| Force of muscle contraction depends on | load; amount of stimuli = summation; # of motor units/ # of cells in motor unit; relative size of muscle; recruitment; degree of stretch/ not stretch; what muscle is attached to |
| The principles governing contraction of a muscle fiber (cell) and of a skeletal muscle consisting of | huge number of cells are pretty much the same |
| Muscle tension | the force exerted by a contracting muscle on an object |
| Load | the opposing force exerted on the muscle by the weight of the object to be moved |
| Isometric (same measure) | if muscle tension develops but the load is not moved |
| Isotonic | if the muscle tension developed overcomes the load and muscle shortening occurs |
| increasing muscle tension | is measured in isometric muscle tension |
| amount of shortening | (distance in millimeters) is measured in isotonic contractions |
| Each muscle | is served by at least one motor nerve, which contains axons (fibrous extensions) of up to hundreds of motor neurons |
| As an axon enters muscle, | it branches into a number of terminals, each of which forms a neuromuscular junction with a single muscle fiber |
| Motor unit | a motor neuron and all the muscle fibers it supplies |
| Myogram | the muscle is attached to an apparatus that produces a graphic recording of contractile activity |
| Tracing | the line recording the activity |
| Muscle twitch | the response of a motor unit to a single action potential of its motor neuron |
| Latent period | first few milliseconds following stimulation when excitation-contraction coupling is occurring. During this period, muscle tension is beginning to increase but no response is seen on the myogram |
| Period of contraction | when cross bridges are active, from the onset to the peak of tension development, and the myogram tracing rises to a peak. This period lasts 10-100 ms. If tension (pull) becomes great enough to overcome the resistance of a load, the muscle shortens. |
| Period of relaxation | lasting 10-100 ms, is initiated by reentry of Ca2+ into the SR. Because contractile force is no longer being generated, muscle tension decreases to zero and the tracing returns to the baseline. If the muscle shortened during contraction, returns inital le |
| Graded muscle responses | Healthy muscle contractions are relatively smooth and vary in strength as different demands are placed on them. The variations are called: |
| Muscle contractions can be graded in two ways | by changing the frequency of stimulation and by changing the strength of the stimulus |
| Wave summation | the second contraction occurs before the muscle has completely relaxed, because the muscle is already partially contracted when the next stimulus arrives and more calcium is being released to replace that being reclaimed by the SR |
| If a second stimulus is receieved before repolarization is complete | no summation occurs |
| Incomplete tetanus | If the stimulus is held at constant and the muscle is stimulated at an increasingly faster rate, the relaxation time between the twitches becomes shorter and shorter, the concentration of Ca2+ in the sarcoplasm higher a sustained but quivering contraction |
| Complete tetanus | As the stimulus frequency continues to increase, muscle tension increases until a maximal tension is reached. At this point all evidence of muscle relaxation disappears and the contractions fuse into a smooth, sustained contraction |
| Recruitment | (blank) |
| Threshold stimulus | (blank) |
| Maximal stimulus | (blank) |
| Treppe | The staircase effect |
Created by:
HeatherJB8