Nervus System Tutorial

Question 1

Does increasing voltage increase action potential?

Answer 1

With higher stimulation voltages there is no change in the size of the action potential (demonstrating the all-or-none law)

Question 2

What is TETRODOTOXIN (ttx)AND LIDOCAINE ?

Answer 2

The results suggest that TTX acts quicker than lidocaine (since in the TTX condition the response has dropped to zero by 6 s while in the lidocaine condition the response doesn’t drop to zero until 8 s. Tetrodotoxin is a neurotoxin derived from pufferfish; lidocaine is a local anaesthetic. Both work by blocking sodium channels, hence preventing transmission of the action potential through the area where the substance was applied.

Question 3

What does Lower Ca ions being released during exocytosis mean ?

Answer 3

Less release of neurotransmitters

Question 4

What does adding Mg ions being released during exocytosis mean ?

Answer 4

Although calcium levels are normal in the extracellular fluid, neurotransmitter release is lower than normal because the magnesium ions have blocked some of the calcium ion channels in the membrane of the terminal button.

Question 5

Does the latent period change with different stimulus voltages.

Answer 5

The latent period doesn’t change with different stimulus voltages. This is because the latent period is the very short period of time between the muscle cell action potential (in this case, triggered by the direct electrical stimulation) and the beginning of the muscle contraction. During this time, various intracellular changes are occurring including calcium ion release from the sarcoplasmic reticulum.

Question 6

Does increases in stimulus voltage result in an increase in the force generated by the muscle ?

Answer 6

Above a certain (threshold) voltage, increases in stimulus voltage result in an increase in the force generated by the muscle. This is because progressively increasing the stimulus voltage activates more and more muscle cells. Above a certain voltage (1.82V in the current experiment), further increases in voltage cause no further increases in muscle contraction force (as all the muscle cells have already been recruited).