Title: Muscle twitch response and recruitment, summation and tetanus Exercise 1: The effects of nerve stimulation Objectives: 1. To explore the motor and sensory effects of electrical stimuli on a student volunteer, using the nerves of the forearm. 2. To examine the position where a largest muscular twich response with the lowest pulse current can be generated. This position is kept constant to determine results in exercises 2 and 3. Procedure: Refer to Human Biology Practical Manual Results: The position giving the largest muscular twitch response with the lowest pulse current can be generated.
Questions: A. Describe briefly what you have done for this section. (maximum 100 words) Powerlab unit is used as a stimulator. Instead of recording, muscular responses are observed by watching hand of volunteer. Stimulus Isolator command is chosen and the settings are set in effect. The stimulator is switched off to disconnect the Isolated Stimulator terminals. The Start button in the Chart View is then clicked. The bar stimulus electrode is placed correctly over the volunteer’s ulnar nerve at the wrist. The Stimulator is switched on.
Twitch contractions affecting thumb and fingers are observed. Small adjustments to placing of electrodes are done and position giving the largest twitches is kept constant throughout the experiment. B. What are the observations that you have made? (maximum 150 words) The bar stimulus electrode is applied with adequate amount of cream before the chart view started. The bar stimulus electrode was placed over the ulnar nerve at the wrist of the volunteer. The chart had been set up to monitor and the stimulator was activated.
The bar stimulus electrode was moved over different positions at the wrist of the volunteer. The thumb of the volunteer twitch at different strength. The twitch of the thumb of the volunteer is involuntary. The largest twitch obtained which response to the volunteer’s thumb is the position of the wrist near the thumb. Exercise 2: Twitch response and recruitment Objectives: 1. To measure the muscular twitch response to nerve stimulation, and to show recruitment in the twitch response as the stimulus strength increases. Procedure: Refer to Human Biology Practical Manual
Questions: A. Describe briefly what you have done for this section. (maximum 100 words) To set up recording, another setting file was opened. The volunteer placed his hand correctly on the surface of transducer. The settings were set in effect. Bar stimulus electrode was holded firmly in place. The stimulus pulse current is set to 0 mA. Start button in Chart View is clicked and a fixed duration of 0. 5 second was set up, then stopped automatically. The pulse current was increased to 1. 0 mA and Start button is clicked until a response is recorded.
The pulse current is reduced by 1 mA and then it was increased in 0. 5 mA steps. A comment is added each time. The steps were continued until response no longer increased. B. What are the observations that you have made? (maximum 150 words) When different stimulus pulses of current applied to the stimulator, different readings of responses were observed. When the stimulus pulse was set to 0. 00 mA, no response was observed. The response remained unchanged at 0. 00 mV. 0. 00 mV of responses were obtained until the stimulus pulse current was set to 7. 0 mA. At the stimulus pulse current of 7. 00 mA, the minimum voltage which causes the first response was observed. The minimum voltage observed was 0. 53 mV. The stimulus pulse current was increased every 0. 5 mA each until 13. 00 mA. The maximum current which cause no further increase in the readings of response were obtained at the stimulus pulse current of 11. 50 mA. The maximum voltage obtained was 31. 20 mV. The readings of the response increased with the stimulus pulse current until maximum voltage was obtained. Exercise 3: Summation and tetanus Objectives:
To demonstrate the effects of changing the interval between paired stimulus pulses, and to observe a short tetanic contraction. Procedure: Refer to Human Biology Practical Manual. Questions: A. Describe briefly what you have done for this section. (maximum 100 words) The settings in the Stimulus Isolator command from Chart’s Setup menu were changed. The box of “set number of pulses”was ticked and the number of pulses was set to “2”. The amplitude was adjusted to the maximum current which causes no increases in the readings of the response which was at 11. 0 mA. The frequency 1 Hz, 2 Hz, 5 Hz, 10 Hz and 20 Hz were manipulated. “Start” button is clicked followed by “stimulate” button to stimulate the electrode to trigger for the response. B. What are the observations that you have made? (maximum 150 words) The frequency was manipulated to 1 Hz, 2 Hz, 5 Hz, 10 Hz and 20 Hz each at different time. “Start” button was pressed followed by “stimulate” button to stimulate electrode to trigger for response. Two peaks of response were observed at the frequency of 1 Hz, 2 Hz and 5 Hz.
The thumb had been twitched for two times in a short duration of time. The contraction of the two pulses on the thumb is fast. The second peak of the respond was higher than the first peak of the response. Whereas for frequency of 10 Hz and 20 Hz, one peak of response was obtained. The thumb had been twitched for two times in an extremely short duration of time. The contraction of two pulses on the thumb is too fast which caused the contraction of thumb of the volunteer only able to response once.