Week 6: Skeletal Muscle Physiology Lab

Why does the active force of skeletal muscle change with the muscle's resting length?

The number of cross-bridges between actin and myosin varies.

Proper muscle contraction requires the concerted interaction of various proteins and cofactors to shorten the sarcomere. Match the words in the left column to the appropriate blanks in the sentences on the right. Words may be used more than once.

The protein Troponin binds to Ca2+ and undergoes a conformational change to initiate contraction. Ca2+ is released from the sarcoplasmic reticulum when the sarcolemma is stimulated by an action potential. Tropomyosin blocks the active site for contractile protein attachment at rest but moves based on the binding state of Troponin. K+/Mg2+ is required to hydrolyze ATP to ADP and Pi.

Which of the following produced an increase in stimulus intensity?

increasing the voltage applied

Increasing the applied voltage in the simulation corresponds to which in vivo event?

motor unit recruitment

Which of the following is NOT a phase of a muscle twitch?

shortening phase

The speed of muscle contraction is called the _______.

shortening velocity

When wave summation occurs, _______.

the muscle force generated increases

Which of the following is proportional to the amount of tension produced by a skeletal muscle?

the number of motor units activated

Which of the following molecules is NOT thought to accumulate during muscle fatigue? -ATP -inorganic phosphate -ADP -lactic acid

ATP

Which of the following describes how increasing the duration of the rest period affected muscle tension?

Increasing the duration of the rest period increased the duration of the subsequent maximal tension.

What might be occurring on a molecular level during the rest periods?

Intracellular ADP and inorganic phosphate are decreasing.

Which of the following occurs if the load attempted is equal to or greater than the force generated by a muscle?

Isometric muscle contraction occurs. Submit

Which of the following occurs during the latent period of isotonic concentric contraction?

Muscle tension is produced, and the weight will not move.

Which of the following is an example of an isometric contraction?

Muscles contracting to support body weight and maintain posture

Which of the following is true of the maximum stimulus frequency?

No greater muscle force can be generated and the muscle has reached maximal tetanic tension.

At which muscle length was the passive force the greatest? -90 mm -100 mm -80 mm -70 mm

100 mm

In the lab, a researcher finds that the threshold stimulus to induce an action potential in a muscle fiber's sarcolemma was 3.0 volts. Which of the following would result in muscle tension?

3.0 volts and 4.0 volts

Which of the following occurs during the contraction phase?

Cross-bridge cycling is taking place.

What is the function of glycerin in this experiment?

It denatures troponin and tropomyosin, so calcium is not needed.

Which of the following describes the relaxation phase?

The sarcomeres are increasing in length, and the force generated decreases.

NO force is generated during which of the following?

the latent period

Which starting length of the muscle provided the maximum total force?

the longest starting length

Which of the following describes the relationship between stimulus frequency and muscle tension?

When stimulus frequency increases, muscle tension increases to a maximum value.

Which of the following is generated when cross-bridges form between actin and myosin?

active force

Muscle twitches overlap with _______.

both fused and unfused tetanus

Which of the following is matched correctly?

complete tetanus - fused tetanus

During muscle fatigue, the ____________ decreases.

force of contraction

Which of the following terms are NOT used interchangeably? in vivo - in the body/ the living motor unit - motor neuron muscle cell - muscle fiber muscle tension - muscle force

motor unit - motor neuron

What is the minimum voltage needed to generate active force in the skeletal muscle?

threshold voltage

When the frequency of stimulation of a muscle is great enough, _______.

wave summation results and muscle twitches overlap.

In this activity, why did the muscle force decrease over time?

Muscle fatigue developed.

Why does wave summation occur?

Muscle fibers are partially contracted when the next stimulus arrives.

Which of the following does NOT describe treppe? -A period of relaxation can be seen on the muscle twitch tracing. -An increase in stimulus intensity is required to see the effect. -An incremental increase in force occurs. -It is also referred to as the "staircase" effect.

An increase in stimulus intensity is required to see the effect.

For a weight to be lifted, which of the following must occur?

An isotonic muscle contraction with a force greater than the load.

Which of the following is NOT a cause of muscle fatigue? -Decreased cellular energy and oxygen -An accumulation of waste products -A build-up of lactic acid -An overproduction of oxygen

An overproduction of oxygen

You are carrying a case of 24 bottles of water up the stairs to your third-story apartment. What type of contraction are the muscles in your arms experiencing?

Passive

When acetylcholine binds to its receptors, it results in __________.

the end plate potential, a graded depolarization, and a change in ion permeability

Which of the following describes the relationship between length and tension?

The active force can increase or decrease, depending on the starting resting length of the muscle.

Match each term listed with the correct description.

Time prior to tension: Latent period Activating more motor units: Recruitment Contraction with rapid relaxation cycles: Incomplete tetanus Response to a single stimulus: Twitch Fusion of twitches: Wave summation Shift in transmembrane potential toward 0 mV: Depolarization

Which of the following occurs during isotonic concentric contraction?

The length of the muscle decreases with contraction.

As the stimulus voltage was increased in this activity, which of the following occurred?

The muscle force generated increased.

Which of the following does NOT describe tetanus? -It can be fused. -The maximum force produced has reached a plateau. -The muscle relaxes fully between contractions. -It can be unfused.

The muscle relaxes fully between contractions.

Treppe is the phenomenon that results in _______.

a progressive increase in the force generated with repetitive stimulation

As the stimulus voltage increased, the resulting muscle tension _______.

increased to a point until it reached a plateau

Which of the following would result in fused or unfused tetanus compared to a single muscle twitch?

increasing the stimulus frequency

Which of the following occurs during the latent period of muscle contraction?

Calcium is released from the sarcoplasmic reticulum.

Which of the following situations delay the development of muscle fatigue the longest? -Consistent interruptions of muscle stimulation -Prolonged muscle contraction -Repetitive stimulation of a muscle -Alternating sprints with up-hill jogging -High intensity exercise

Consistent interruptions of muscle stimulation

Which of the following produced an increase in stimulus frequency?

clicking the mouse in rapid succession

To transition from unfused tetanus to fused tetanus, _______.

stimulus frequency increased

At what stimulus frequency was maximal tetanic tension developed?

146 stimuli/sec

A drug was developed and approved for the treatment of numerous disorders of muscle stiffness and muscle spasms. The cosmetic use of this drug is to temporarily reduce forehead frown lines. This new drug works by blocking the release of the neurotransmitter at the neuromuscular junction. Which neurotransmitter is blocked?

Acetylcholine

As you saw in the video, actin and myosin are the primary contractile proteins involved in shortening the sarcomere. Each protein has special characteristics that allow it to participate in the sliding filament mechanism of muscle contraction. Drag the appropriate items to their respective bins.

Actin: thin filament, composed of monomeric subunits with myosin-binding sites, thin filament, regulated by troponin and tropomyosin Myosin: thick filament, composed of molecules with heads that pivot and bend, hydrolyzes ATP to ADP and Pi to form a crossbridge

Match the type of articulation with the best description of either its functionality or arrangement of tissue.

Also known as an 1Cimpulse, 1D a(n) Action potential is an electrical signal that is produced on excitable membrane such as muscle and nerve tissue. Neurotransmitters are chemicals released at the synaptic terminal of a neuron that can transmit an impulse to a muscle fiber. A muscle fiber is either contracted or it's not. This is the All-or-none principle. A runner competing in the 50-yard dash has muscles in the legs that are undergoing Complete tetanus. A Motor unit is described as all the muscle fibers controlled by the same motor neuron. Recruitment is the process by which a muscle produces more force to pick up a brick verses a feather.

Match each term listed with the correct description.

Reduction in contraction and performance: Fatigue Neurotransmitter: Acetylcholine Tension changes more than length: Isometric contraction Length changes more than tension: Isotonic contraction Return of membrane to resting potential: Repolarization Contraction with no relaxation cycles: Complete tetanus

The resting length of the muscle _______.

occurs when the muscle is relaxed

Where does the acetylcholine that stimulates muscle contraction bind?

receptors in the motor end plate

Which of the following can trigger a muscle twitch?

release of acetylcholine or electrical stimulation

A motor unit is defined as _______.

the axon terminals of a single motor neuron and all of the muscle fibers that it stimulates

The graph of the length-tension relationship illustrates _______.

the optimal sarcomere length for muscle contraction and the amount of overlap between the thick and thin filaments in the resting muscle