[PhysioEX Chapter 3 exercise 8] PEX-03-08

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Exercise 3: Neurophysiology of Nerve Impulses: Activity 8: Chemical Synaptic Transmission and Neurotransmitter Release
Lab Report
Pre-lab Quiz Results
You scored 100% by answering 5 out of 5 questions correctly.

1. The end of the axon where it contacts a target is called the
   You correctly answered: c. axon terminal.
2. Neurotransmitter is released into the synaptic gap by
   You correctly answered: a. exocytosis.
3. Exocytosis of neurotransmitter from the axon terminal is triggered by an increase in the intracellular concentration of
   You correctly answered: c. Ca2+ .
4. Neurotransmitter released into the synaptic gap reaches the target cell by
   You correctly answered: b. diffusion.
5. At the target, neurotransmitter
   You correctly answered: d. does all of the above.

Experiment Results
Predict Question:
Predict Question 1: You have just observed that each action potential in a burst can trigger additional neurotransmitter
release. If calcium ions are removed from the extracellular solution, what will happen to neurotransmitter release at the axon
terminal?
Your answer : c. There will be less neurotransmitter release.
Predict Question 2: What will happen to neurotransmitter release when low amounts of calcium are added back to the
extracellular solution?
Your answer : b. Neurotransmitter release will increase a small amount.
Predict Question 3: What will happen to neurotransmitter release when magnesium is added to the extracellular solution?
Your answer : a. There will be no neurotransmitter release.
Stop & Think Questions:
Why does the stimulus intensity affect the amount of neurotransmitter release at the axon terminal?
You correctly answered: d. Both a and b are correct.
Why is there no neurotransmitter release from the axon terminal when there are no calcium ions in the extracellular
solution?
You correctly answered: c. Exocytosis of the synaptic vesicles is calcium dependent.
Why did the high intensity stimulation fail to trigger the same amount of neurotransmitter release in the presence of
extracellular Mg2+ as in the control extracellular solution?
You correctly answered: a. Mg2+ blocks the calcium channels in the axon terminal.
Experiment Data:

Post-lab Quiz Results
You scored 100% by answering 4 out of 4 questions correctly.

1. How is the neurotransmitter stored in the axon terminal before it is released?
   You correctly answered: c. contained in synaptic vessicles
2. Are neurotransmitter molecules released one at a time or in packets?
   You correctly answered: b. in packets
3. With the normal extracellular calcium concentration, [Ca2+ ], when the action potential reaches the axon terminal it
   triggers
   You correctly answered: b. release of neurotransmitter by exocytosis.
4. Comparing the low intensity stimulus to the high intensity stimulus, the high intensity stimulus causes
   You correctly answered: b. more synaptic vesicles to undergo exocytosis

Review Sheet Results

1. When the stimulus intensity is increased, what changes: the number of synaptic vesicles released or the amount of
   neurotransmitter per vesicle?
   Your answer:
   Increasing stimulus intensity makes more number of synaptic vesicles be released.
2. What happened to the amount of neurotransmitter release when you switched from the control extracellular fluid to the
   extracellular fluid with no Ca2+ ? How well did the results compare with your prediction?
   Your answer:
   decresed, as predicted
3. What happened to the amount of neurotransmitter release when you switched from the extracellular fluid with no Ca2+
   to the extracellular fluid with low Ca2+ ? How well did the results compare with your prediction?
   Your answer:
   increase a small amount, as predicted.
4. How did neurotransmitter release in the Mg2+ extracellular fluid compare to that in the control extracellular fluid? How
   well did the result compare with your prediction?
   Your answer:
   neurotransmitter relesade, contradicting with my prediction
5. How does Mg2+ block the effect of extracellular calcium on neurotransmitter release?
   Your answer:
   it blocks the calcium channels and inhibits the release of neurotransmitter.