Lab 05 Assignment

Name: Nathan Pereira ID 169029922 Lab Day and Time: Tuesday 4:30 Lab #5 Muscle Physiology Assignment Data Submission: As a group , using your data from Exercise Twitch Response and Recruitment, graph the Stimulus Intensity versus the Twitch Peak Force output. (Submitted via Dropbox, as a group, due at 11:59pm) (4 marks) Both individuals on the same graph In Lab Assignment: 1. What is the relationship between the Stimulus Strength and the Twitch Peak Force according to your data? (1 mark) - There is a positive relationship between the strength of the stimulus and the twitch peak force - As the strength of the stimulus increases the peak force created was also higher. 2. What is the physiological basis of this relationship? (What is happening in the body to cause the response, and why is the response changing as the stimulus strength changes)? (2 marks) - The recruitment of additional motor units leads to an increased number of muscle fibers contracting simultaneously, contributing to a higher peak force. - The force of muscle contraction is highly dependent on the availability of calcium ions. - A stronger stimulus leads to increased calcium ion release from the sarcoplasmic reticulum, promoting the interaction between actin and myosin and thereby increasing force production. 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? (1 mark) - Yes we did notice this... - The stimulus did not meet the threshold to cause an action potential, so this is why no response was observed. 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? (1 mark) - Yes, when the stimulus strength reached 17 all reached around the same level of peak - This is because the motor units in the ulnar nerve are all recruited to produce the force that we see and were using all the motor units that are currently available at the time. 1

- This would mean that when a high enough amplitude has been reached all the motor units are used and the stimuli’s can’t get any more intense, or elicit any more of a response. 5. List your recorded values below (2 marks) Participant A Participant B Stimulus Amplitude (mA) Twitch Peak Force (mV) 5 0 6 0 7 0 8 0 9 0 10 0 11 0 12 0 13 11.09 14 31.45 15 38.29 16 77.53 17 95.32 18 114.25 19 98.56 20 104.29 Stimulus Amplitude (mA) Twitch Peak Force (mV) 5 0 6 0 7 0 8 0 9 0 10 0 11 0 12 0 13 5.63 14 6.54 15 6.93 16 8.85 17 11.83 18 21.13 19 35.26 20 50.48 6. 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? (4 marks) - The stimulus that comes first is still lingering when the second stimulus happens in short succession the two stimuli get added. The closer in time that the stimuli happen the more stimulus gets added to the second - Because of this the second force has a higher peak because it is the addition between whets left of the force of stimuli one and stimuli two. - In rapid succession of stimuli, the concentration of calcium ions in the muscle cytoplasm can accumulate since there is less time for them to be pumped back into the sarcoplasmic reticulum - The elevated levels of calcium ions facilitate more cross-bridge formations between actin and myosin filaments. 2