Lab 2 - Skeletal Muscle Physiology (P. 17)

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In this lab, I will study how muscles contract, what makes muscles contract, different types of muscle contraction, and learn about how resistance affects muscle contraction. I will define Key Terms that describe what will occur in the experiments; I will conduct an experiment for each Activity and provide all resulting Data as well as answer Questions from each Activity. I will then provide a short Summary for what I learned in each Activity.

Key Terms:
Recruitment (or Multiple Motor Unit Summation) (p. 18) - greater number of motor units are present in a muscle and are able to be simultaneously stimulated causing an increase in muscle force Latent Period (p. 18) - The interval between stimulus and response. Isometric Contraction (or Fixed Length Contraction) (p. 20, 23 in Lab Manual; p. 963 - Hole's) - A contraction in which muscle tension is increased, but the muscle is not. Treppe (or Staircase Effect) (p. 20) - The occurrence of a successive increases in the extent of contractions following rapid, repeated stimulation of a muscle. Wave Summation (p. 21) - The combination of responses from a motor unit that has had two or more stimuli applied to it in quick succession.

Tetanus (p. 21) - A state of continuous muscular contraction, especially when induced artificially by rapidly repeated stimuli. Muscle Fatigue (p . 23) - Muscle fatigue is the repeated, intense use of muscles which leads to a decline in performance.Though the actual mechanism for muscle fatigue appears to involve the leakage of calcium. Passive Force (p. 23) - Any movement produced by a force that is external to the muscle or muscle group normally responsible for the movement. Active Force (p. 23) - A force due to movement entirely controlled by muscular activity. Total Force (p. 23) - The process by which multiple or repeated stimuli can produce a response in a nerve, muscle, or other part that one stimulus alone cannot produce. Isotonic Contraction (p. 25) - Of or involving muscular contraction in which the muscle remains under relatively constant tension while its length changes.

FIGURE 2.1 Single stimulus and muscle twitch.
(a) Opening screen of the Single Stimulus experiment. (b) The muscle twitch: myogram of an isometric twitch contraction. (PhysioEx 8.0 for A&P: Laboratory Simulations in Physiology. Pearson Learning Solutions).

Activity 1: Practicing Generating a Tracing

No Data for This Activity (practice generating tracings)

No Questions For This Activity

In this Activity, I learned how to produce a tracing of muscle activity following stimulation.

Activity 2: Determining the Latent Period



2-1: How long is the latent period? In other words, how much time elapses before the active force reading moves? __2.78____ msec

2-2: What occurs in the muscle during this apparent lack of activity? (Hint: something IS occurring; see p. 18) During the latent period calcium is being released from the sacroplasmic reticulum; which stores ATP, and filament movement is taking up slack.


In this Activity, I learned/observed that: During the brief latent period the stimuli is circulating and sending signals for an appropriate response. The electrical signal gets passed up the cell membrane and other channels open.

Activity 3: Investigating Graded Muscle Response to Increased Stimulus Intensity



3-1: What is the minimal, or threshold stimulus? In other words, when does active force start? __ around 0.8 ___ V

3-2: What is the maximal stimulus? In other words, when is the stimulus maximized (not the highest it can go but the highest active force you see)? __8.0______V

3-3: How can you explain the increase in force that you observe? Stimulus intensity is the strength of the apmlitude of the stimulus. Stimulus frequency is the number of times per unit time that the stimulus is presented....
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