Frog Gastroenemius Musele Lab Report Name Graphs: Make sure you collect data to
ID: 3512671 • Letter: F
Question
Frog Gastroenemius Musele Lab Report Name Graphs: Make sure you collect data to construct the following graphs. art 1.Stimulus (volts) vs Tension developed (grams) Part 2 Stimulus frequency (Hz) vs Tension developed (grams) Part 1. Twitch Responses Threshold voltage u Force generated Duration of twitch contraction3Duration of twitch contraction6 Latent period (time from stimulus to twitch) aaus Latent periodou Maximal voltage Force generated . - 1. Describe the events taking place that result in the "latent period," the time from stimulating the nerve to muscle contraction. 2. What do you think is happening as you increase voltage from threshold to the maximal voltage? Why does the force generated by the whole muscle increase? (Remember the sciatic nerve is a bundle of axons).Explanation / Answer
1. A muscle twitch has 3 phases: 1) the latent period; 2) the contraction period; 3) the relaxation period. The latent period is the time between the initiation of electrical stimulus and the initiation of muscle contraction. This latency period is required for electrical coupling to occur. In electrical coupling, the entry of Ca2+ into the muscle fibers activates actin-myosin cross-bridges.
a) action potential moves across the sarcolemma.
An impulse from the nerve reaches a motor unit through the motor neuron at the neuromuscular junction. The nerve releases calcium into terminal buttons that results in release of acetylcholine (Ach). Ach bind with the receptors on the sarcolemma and opens up the sodium channels in the sarcolemma, resulting in a change in resting potential. The sarcolemma will depolarize.
b) Depolarization of sarcolemma traverses down the muscle fiber via the transverse tubule system. As a result, ryanodine receptor open and the sarcoplasmic reticulum release calcium into the cytoplasm. This action increases calcium level in cytosol. Calcium binds to troponin C, and removes tropomyosin from the blocking the actin-myosin binding site. There is a change in troponin, which results in shifting of trophomyosin and active sites on actin are unblocked. This will allow myosin heads to involve in cross bridge formation.
2. When the intensity is increased beyond the threshold, the muscle contraction will increase. Threshold is the level of stimulation required to trigger the smallest measurable contraction. This is a result of excitation and contraction of the first few muscle fibers. However as the stimulus reaches a particular maximal level, muscle contraction will remain constant. This stimulus is the maximal stimulus where all of the fibers in the muscle are stimulated. These muscle respond in all-or-none fashion. Supramaximal stimuli are stimuli above the maximal stimulus while subthreshold stimulus is stimulus below the threshold where there is no mechanical response.
The force generated by a muscle depends on the size and number of motor units. As the stimulus increases, the number of motor units stimulated increases. Each motor unit has a motor neuron associated with a number of muscle fibers. When a motor unit is stimulated, all the motor fibers associated with it will respond. The sciatic nerve is a bundle of axons. As the voltage is increased, more and more impulses are generated by stimulation of the axons. The impulses will reach the neuromuscular junction and release increasing amounts of acetylcholine. As a results, more motor fibers get stimulated and the force generated in the muscle increases. However, at the supramaximal level, all the axons are generating impulses and all the muscle fibers are stimulated to the maximum. Hence, the force generated will reach a constant value.
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