Introduction (including aims)
•provide a relevant and concise referenced background to the EMG and reflex experiments
•400 – 500 words
Part A – EMG
•group data for exercise 1 and 2
•class data for CV
Part B – Reflexes
•briefly describe your observations from the reflex experiments conducted
Part C – Equilibrium
•briefly describe the nystagmus and sensations reported
Questions (no formal discussion section required)
Part A – EMG
Q1. Unlike the discrete waveform from an electrocardiogram, the electromyogram waveform is irregular. Why do you suppose this is?
Unlike, the heart , skeletal muscle does not contract in all or none fashion . instead , an EMG is recording the electrical activity of many muscle fibers .
Q2. Based on the data you collected what can you infer is happening to the muscles as weight is added?
Q3. what is co-activation? What is an explanation for this phenomenon?
Co-activation as a small increase in activity in a non-active muscle is in opposition to a muscle that is contracting forcefully.
The reasons for Co- activation are unclear, but it is possible it is aids in joint stabilization.
Q4. List the physiological events that occur between delivery of the electrical stimulus and the start of the recorded response; that is, during the latent period.
Initiation of action potential in nerve fibers; conduction of impulse;
Release of acetylcholine from the nerve terminals. Binding of acetylcholine to receptors of the motor end plate;
Depolarization of the end plate ;
Initiation of action potential in muscle fibers ;
Muscle contraction .
Q5. Which of these depends on the position of the stimulating electrode?
Q6. Based on your results and calculations for nerve conduction velocity, how long would it take for a nerve impulse to travel from the spinal cord to the big toe (assume that the distance travelled is 1.2 metres) ?
Conduction velocity varies among nerves , but can be as high as 100 m/sec. at the rate , it would take 10 milliseconds(0.01) sec 0 for a nerve impulse to travel one meter.
Part B – Reflexes
Q7. What effect did conscious inhibition and the Jendrassik manoeuvre have on patellar reflex amplitude? Why did this occur?
It increases the reflex, as the subject is distracted by performing the manoeuvre and is said to prevent conscious anticipation of the reflex. Generally it should cause an increase in the duration and the magnitude of the reflex.
Q8. What is the receptor for this reflex response? Draw a diagram the reflex pathway involved.
Q9. Why is the stretch reflex you have demonstrated an example of a phasic reflex response, and an example of a negative feedback system?
Q10. What is the receptor for the TVR reflex and what sensory information is being provided to the CNS?
Q11. In a patient whose spinal cord has been transected at the level of L2 a knee jerk response should be elicited, but not a tonic vibration reflex (TVR). In what way must the reflex arc which produces the TVR differ from that for the knee jerk response?
Q12. What is the neurophysiological mechanism that could account for changes observed in the biceps and triceps vibration experiments?
Q13. What is the purpose of crossed extensor reflexes?
Q14. What were your observations regarding pupillary reflexes. Why do they occur?
Q15. Define nystagmus.
Q16. Why did the subject still report a sense of rotation after the rotation had stopped?
Human Anatomy & Physiology – Elaine Marieb & Katja Hoehn – 8th ed
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