PS-145Study questionsDr. S.H. Chandler #6

1. What does it mean to “load compensate”. Why is load compensation during mastication important? If you were to foolishly try to crush a jaw breaker, you typically don’t crack your lower jaw teeth on the upper jaw, why?

2. What is the role of gamma MNs in the CNS ? What is the difference in how the brain presets gamma motoneurons for the agonist and antagonist muscles prior to a voluntary movement? Why is this important? How does the brain encode for jaw joint angle?

3. When the doctor takes a reflex hammer and briskly taps your patellar tendon, you typical extend the leg? Why? Suppose you were very tense when she did that, how might the response differ?

4. Without looking at your notes--Draw a steady state Frequency-I plot obtained from pulse current stimuli for a spinal and jaw extensor motoneuron. Why might they differ? How would you determine if a persistent Na current is active just prior to spike threshold?

5. Why might we use the ramp stimulus method to generate a F-I plot? Without looking at your notes, if you gave a ramp stimulus and made a subsequent F-I plot that was linear in both directions with same threshold, what would you reasonably conclude about its discharge pattern in response to a series of Suprathreshold step pulses? Suppose that you observe no hysteresis and found that the curve was linear but the down ramp frequency threshold was lower than the up ramp frequency. What do you hypothesize about the underlying currents? Any different from the first scenario?

6. What are Mes V neurons so unique? What might be the functional consequence for this? Compare and contrast them to Ia afferent cells in DRG.

7. How would you show using only electrical stimulation that there is a stretch reflex in jaw closer MNs? How would you test for one in jaw openers? Explain specifically the methods as well.

8. Propose a 1) physiological, and 2) anatomical experiment to demonstrate electrical coupling between neurons A and B. Why is the recorded voltage response so much smaller in the non-stimulated neuron? Does this type of communication occur in the trigeminal system and why might this be important?

9. Some scientists believe that electrical coupling between neurons is important for production of rhythmical activity in a CPG circuit. What evidence is there for this idea? Be specific.

10. What is the purpose of reciprocal inhibition mediated by Ia afferents for limb movements? How does this differ during jaw movement? If there is a difference, why and be specific?

11. Outline the anatomical pathways from intra-oral receptor to the region of the sensory cortex for perception of touch of the lips.

12. (review)What is the role for low threshold IA current with respect to a) spike frequency control and b) frequency of bursting during locomotion?

Have a nice weekend!