lab midterm #3

Question 1

What was the relationship between stimulus amplitude and response amplitude in the Evoked EMG activity?

Answer 1

The relationship between stimulus amplitude and response amplitude in evoked EMG activity is positive—as stimulus amplitude increases, response amplitude also increases.

However, this relationship is nonlinear:
* At low stimulus amplitudes, the response is small or absent.
* As stimulus amplitude increases, the response grows as more motor units are recruited.
* At high stimulus amplitudes, the response amplitude reaches a plateau because all available motor units have been activated.

Question 2

What is the physiological basis of the above relationship? (What is actually happening in the body to cause the response, and why is the response changing as the stimulus strength changes)?

Answer 2

• Threshold Phase (Low Stimulus Amplitude) – At very low stimulus amplitudes, there is little or no response, as the stimulus is not strong enough to activate motor neurons or muscle fibers.
• Recruitment Phase (Increasing Stimulus Amplitude) – As the stimulus amplitude increases, more motor units are recruited, leading to a gradual increase in response amplitude. This phase is often nonlinear due to factors like recruitment order (smaller motor units are activated first, followed by larger ones).
• Saturation Phase (High Stimulus Amplitude) – Eventually, the response amplitude reaches a plateau, as all available motor units have been recruited. Increasing the stimulus amplitude beyond this point does not result in a further increase in EMG response.

Question 3

In the Evoked EMG activity, what would the physiological explanation be for a stimulus that elicited no response?

Answer 3

In evoked EMG activity, a stimulus that elicited no response is due to insufficient depolarization of motor neurons or muscle fibers. The physiological explanations for this include:
1. Subthreshold stimulus
2. Ineffective nerve or muscle activation
3. Nerve conduction block or fatigue
4. Excessive resistance or poor conductivity
5. Absolute refractory period

Question 4

In the Evoked EMG activity, what would the physiological explanation be for multiple stimuli of varying strength eliciting roughly the same strength of response to each stimulus?

Answer 4

If multiple stimuli of varying strength elicit roughly the same strength of response in an evoked EMG activity, the likely physiological explanation is that the response has reached a saturation point, meaning that all available motor units have already been recruited