Muscle Twitch Response and Recruitment, Summation and Tetanus.

Experiment 1: Muscle twitch response and recruitment, summation and tetanus.

Exercise 1: The effects of nerve stimulation

A. Describe briefly what you have done for this section.

The objective for this part of experiment is to investigate the motor and sensory effects of electrical stimuli on a volunteer by using the nerves of the forearm. In this exercise, the stimulator has been set according to a specific frequency (1 Hz), pulse duration (200 µs) and pulse current (10 mA). Later, the bar stimulus electrode is placed over volunteer’s ulnar nerve at the wrist along the axis of the arm. When the largest twitch contraction affecting the thumb and fingers has been observed, the electrode will be placed there and ready for the next exercise of the experiment.

B. What are the observations that you have made?

Exercise 2: Twitch response and recruitment

A. Describe briefly what you have done for this section.

B. What are the observations that you have made?

C. Please provide answers to the following questions.

1. Did you get a measurable twitch with stimulus of 0 mA?

No, since there was no response observed at stimulus of 0 mA (no twitching).

2. What was the smallest current required to produce a contraction (the threshold current)?

5.5 mA

3. What was the smallest current required to produce the maximum (largest) contraction?

8.0 mA

4. What happened to the number of fibers contracting as the current was raised from threshold to that required to produce a maximal contraction?

5. Why does varying the stimulus strength affect the twitch force?

D. Please fill-in the following Table.

Table 1: The effects of varying stimulus strength on twitch force.

|Stimulus (mA) |Response (mV) |Stimulus (mA) |Response (mV) |

|0.0 |0.00...