Physiology Lab #2 Skeletal Muscle Physiology Review

Does the duration of the latent period change with different stimulus voltages?

No, the duration of the latent period didn't really change.

What happens to the amount of total force the muscle generates during the stimulated twitch?

The amount of total force decreased when the length of the muscle both increase and decrease passed its resting length. However, when the muscle was stretched to 100mm, it exceeded the total force than that of the resting length.

How did the frequency of stimulation affect the amount of force generated by the isolated skeletal muscle when the frequency of stimulation was increased such that the muscle twitches did not fully relax between subsequent stimuli? Are these results called treppe or wave summation?

The amount of total force generated by the isolated skeletal muscle inscreased when stimulus frequency increased with no relaxation of the muscle in between. This is called wave summation.

What are some proposed causes of skeletal muscle fatigue?

The buildup of lactic acid, ADP, and Pi in the muscle fibers.

When a skeletal muscle fatigues, what happens to the contractile force over time?

The contractile force declines because of the previous contraction.

Describe the three phases of a skeletal muscle twitch.

*latent period- period of time that elapses between the generation of an action potential in a muscle cell and the start of muscle contraction. *contraction phase- starts at end of the latent period and ends when muscle tension peaks. *relaxtion phase- the period of time from peak tension until the end of the muscle contraction.

List a few ways that humans could delay the onset of fatigue when they are vigorously using their skeletal muscles.

- allow for multiple times of rest - good amount of exercise to train endurance.

How is this change in whole-muscle force achieved in vivo?

A steady increase in muscle force increases based on the amount of electrical current given. It still goes through threshold voltage and once the voltage goes beyond threshold, a whole muslce force occurs. Maximal voltage still takes place in vivo. tension. Whole-Muscle Force is achieved in Vivo by recruitment of additional motor units that increase the total muscle force produced.

Based on the unique arrangement of myosin and actin in skeletal muscle sarcomeres, explain why active force varies with changes in the muscle's resting length.

Active force data changes as the resting length of the muscle changes. The change in the active force amount is completely caused by the amount of myosis bound to actin. The shorter the muscle's resting length is, the more myosis filaments bind to actin filaments.

Describe how increasing the stimulus frequency affected the force developed by the isolated whole skeletal muscle in this activity.

Increasing the stimulus frequency lead to an increase in active force generated by the whole skeletal muscle. Active force began to pleatu and maximal tetanic tension occurred.

What is the role of acetylcholine in a skeletal muscle contraction?

It binds to receptors and initiates a change in ion permeability that results in the contraction of the muscle cell.

Explain why it would take you longer to perform 10 repetitions lifting a 10-kg weight than it would to perform the same number of repetitions with a 5-kg weight.

It takes longer to perform 10 reps lifting 10-kg than 5-kg, because with 5-kg, maximal shortening velocity is attained much faster. The heavier, the load, the slower the muscle twitch and the lighter the load, the faster the muscle twitch.

What skeletal muscle lengths generated passive force? (Provide a range.)

Muscle lengths of 80mm-100mm generated passive force.

At the threshold stimulus, do sodium ions start to move into or out of the cell to bring about the membrane depolarization?

Sodium ions move into the cell to bring about the membrane depolarization.

In this experiment you observed the effect of stimulating the isolated skeletal muscle multiple times in a short period with complete relaxation between the stimuli. Describe the force of contraction with each subsequent stimulus. Are these results called treppe or wave summation?

Stimulating the isolated skeletal muslce multiple times in a short period with complete relaxation resulted in an increase of contraction force. This result is called treppe.

What is the difference between stimulus intensity and stimulus frequency?

Stimulus intensity describes the amount of force generated to administer the stimulus while stimulus frequency refers to the rate of delivered stimulus to the muscle.

What is the key variable in an isometric contraction of a skeletal muscle?

The fixed length of the skeletal muscle.

What happened in the isolated skeletal muscle when the maximal voltage was applied?

The isolated skeletal muscle became depolarized and all fibers became involved in active force when maximal voltage was reached.

Explain why the latent period became longer as the load became heavier in the experiment.

The latent period became longer because of the decrease of muscle twitch duration and velocity. In other words, the muscle length doesn't shorten as much with the heavier loads.

Describe the effect of increasing stimulus voltage on isolated skeletal muscle. Specifically, what happened to the muscle force generated with stronger electrical stimulations and why did this change occur?

The muscle force increased as the voltage increased but once it receached the maximal voltage, the force of contraction stopped increasing and stayed the same even though you keep increasing voltage.

Beyond what stimulus frequency is there no further increase in the peak force? What is the muscle tension called at this frequency?

There was not further increase in peak force wiht stimulus frequency of 140+ Maximal Tetanic Tension

Describe what would happen in the following experiment: A 2.5-g weight is attached to the end of the isolated whole skeletal muscle used in these experiments. Simultaneously, the muscle is maximally stimulated by 8.5 volts and the platform supporting the weight is removed. Will the muscle generate force? Will the muscle change length? What is the name for this type of contraction?

This is an isometric contraction. The muscle would generate passive force when given an electrical stimulus but with the weight pullin down on the muscle, the muscle would not visibly move. Since the weight is puling down on the muscle, the muscle is going to lengthen but not because of a contraction, but because of the weight just pulling down on it.

Describe the process of excitation-contraction coupling in skeletal muscle fibers.

This is th process of neuromuscular junction which then leads to the end-plate potential. The motor neuron then releases acetylcholine when the action potential is reached which causes a diffusion in the muscle fibers and from there binds to receptors which change ion permeabilty resulting in the contraction of the muscle cell.

To achieve an active force of 5.2 g, did you have to increase the stimulus voltage above 8.5 volts? If not, how did you achieve an active force of 5.2 g?

To achieve active force of 5.2g, you did not have to increase stimulus voltage above 8.5. To achieve active force of this amount, you had to increase stimulus frequency.

Compare and contrast frequency-dependent wave summation with motor unit recruitment (previously observed by increasing the stimulus voltage). How are they similar? How was each achieved in the experiment? Explain how each is achieved in vivo.

Wave summation releases more calcium and increases the force of contraction by increasing the firing rate of motor neurons using one muscle fiber.Recruitment use multiple motor units, in order to increase the force of contraction. There is no added calcium ions as in wave summation. Summation was achieved by firing stimuli over and over before relaxtion of the muscle causing more force recruitment was achieved by rapid firing of stimuli to get max sooner.

If you were using your bicep muscles to curl a 7-kg dumbbell, when would your muscles be contracting isotonically?

When ligting the dumbell toward your shoulder.

If you were curling a 7-kg dumbbell, when would your bicep muscles be contracting isometrically?

When the bicep muscle remains at a fixed length.

Turning the stimulator off allows a small measure of muscle recovery. Thus, the muscle will produce more force for a longer time period if the stimulator is briefly turned off than if the stimuli were allowed to continue without interruption. Explain why this might occur.

When the stimulator is off,there is a period of rest. This allows concentrations of Lactic acid,ADP, and Pi to decreaase. With these concentrations being at a decreased level, the length of time that the muscle is able to maintain maximum tension increases. If the stimulator was not turned off for a short time, the muscle would not be allowed to reach a rest period and further fatigue would continue.

Explain why the shortening velocity became slower as the load became heavier in this experiment.

When the weight is heavy, the speed in which the muscle lifts the weight decreases in speed at a slower velocity.

Describe how the shortening distance changed as the load became heavier in this experiment.

With an increase in weight, the shortening distance became shorter.

Indicate what type of force was developed by the isolated skeletal muscle in this activity at the following stimulus frequencies: at 50 stimuli/sec, at 140 stimuli/sec, and above 146 stimuli/sec.

Your answer: 50- Unfused Tetanus 140-Fused Tetanus 146+ Maximal Tetanic Tension

motor unit

consists of a motor neuron and all of the muscle fibers it innervates

skeletal muscle fiber

individual skeletal cells

electrical stimulus

the elicitation of muscle contraction using electric impulses.

skeletal muscle twitch

the mechanical response to a single action potential

latent period

the period of time that elapses between the generation of an action potential in a muscle cell and the start of a muscle contraction