lab midterm #5

Question 1

1. What is the relationship between the Stimulus Strength and the Twitch Peak Force according to your data in the twitch response and recruitment exercise?

Answer 1

• Initial Phase: As stimulus strength increases, more motor units are recruited, and twitch peak force increases.
• Plateau Phase: Once all motor units are recruited, the twitch peak force reaches a maximum and no longer increases despite stronger stimuli

Question 2

2. What is the physiological basis of this relationship for in the twitch response and recruitment exercise? (What is happening in the body to cause the response, and why is the response changing as the stimulus strength changes)?

Answer 2

Motor Unit Recruitment (Principle of Recruitment)
* Motor units are the basic functional units of muscle contraction, each consisting of a motor neuron and the muscle fibers it innervates.
. All-or-Nothing Principle
* Action potentials in motor neurons follow the all-or-nothing principle, meaning that if the stimulus reaches the motor neuron’s threshold, it will fire an action potential, and all muscle fibers within that motor unit will contract.
Twitch Contraction and Force Production
* Twitch contraction is the response of a single motor unit when stimulated
Physiological Basis for the Change in Response
* Stimulus strength determines how many motor units are recruited. At low stimulus strength, only a small number of units are activated, producing a small force.

Question 3

3. During data collection, at the lower stimulus strengths, did you have any occurrences where you applied a stimulus, but no response was observed? What is the physiological reason for this

Answer 3

This phenomenon occurs because the stimulus strength was not sufficient to reach the threshold required to activate the motor neurons and elicit a muscle response

Question 4

4. During data collection, at the higher stimulus strengths, did you have any occurrences where multiple stimuli of varying strength elicited roughly the same response? What is the physiological reason for this?

Answer 4

• Higher stimulus strengths lead to saturation of motor unit recruitment, where all available motor units are recruited and contributing to the response.
• After this point, increasing the stimulus strength does not increase the force of contraction because no additional motor units can be recruited.
• This results in roughly the same response across multiple stimuli once the maximum motor unit recruitment has been achieved.

Question 5

5. According to the Summation Exercise, why does the peak force of the 2nd force response increase as the time between stimulation pulses decreases? Specifically, what happens within the muscle fiber to make the second and third responses bigger than the first response?

Answer 5

• When two or more stimuli are delivered in rapid succession (with a short time interval between them), the second stimulus arrives before the muscle fiber has completely relaxed from the first contraction.
• This leads to summation, where the second contraction adds to the first, resulting in a larger overall force.