Neurophysiology of Nerve Impulses Report

Lab Report Neurophysiology of Nerve Impulses 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: axon terminal. 2 Neurotransmitter is released into the synaptic gap by You correctly answered: exocytosis. 3 Exocytosis of neurotransmitter from the axon terminal is triggered by an increase in the intracellular concentration of You correctly answered: Ca . 2+ 4 Neurotransmitter released into the synaptic gap reaches the target cell by You correctly answered: diffusion. 5 At the target, neurotransmitter You correctly answered: does all of the above. Experiment Results Predict Questions 1 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: There will be no neurotransmitter release. 2 Predict Question 2: What will happen to neurotransmitter release when low amounts of calcium are added back to the extracellular solution? Your answer: Neurotransmitter release will increase a small amount. 3 Predict Question 3: What will happen to neurotransmitter release when magnesium is added to the extracellular solution? Your answer: There will be no neurotransmitter release. Stop & Think Questions 1 Why does the stimulus intensity affect the amount of neurotransmitter release at the axon terminal? You correctly answered: Both "The stimulus intensity directly affects the amount of calcium entering the axon terminal." and "The stimulus intensity proportionally affects the number of synaptic vesicles that discharge their contents into the synaptic cleft." are correct. 2 Why is there no neurotransmitter release from the axon terminal when there are no calcium ions in the extracellular solution? You correctly answered: Exocytosis of the synaptic vesicles is calcium dependent. 3 Why did the high intensity stimulation fail to trigger the same amount of neurotransmitter release in the presence of extracellular Mg You correctly answered: Mg as in2+the control extracellular solution? 2+ blocks the calcium channels in the axon terminal. 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: contained in synaptic vessicles. 2 Are neurotransmitter molecules released one at a time or in packets? You correctly answered: in packets. 3 With the normal extracellular calcium concentration, [Ca ], when2+the action potential reaches the axon terminal it triggers You correctly answered: release of neurotransmitter by exocytosis. 4 Comparing the low intensity stimulus to the high intensity stimulus, the high intensity stimulus causes You correctly answered: 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: When the stimulus intensity is increased, the number of synaptic vesicles released increases as well. In the experiment, we filled the petri dish with extracellular solutions such as control Ca2+, no Ca2+, low Ca2+, and Mg2+. These four solutions were filled into the petri dish (with a neuron inside) separately by themselves each time to then observe the neurotransmitter release from the axon terminal. In the Ca2+, low Ca2+, and Mg2+ solutions, stimulating the neuron in low intensity only promoted little release of neurotransmitter. However, more were released when the intensity was turned on to high. As for the no Ca2+ solution, nothing happened because there were no Ca2+ present to stimulate the release of neurotransmitter. 2 What happened to the amount of neurotransmitter release when you switched from the control extracellular fluid to the extracellular fluid with no Ca ? How 2+ well did the results compare with your prediction? Your answer: No neurotransmitter was released when I switched from the control extracellular fluid to the extracellular fluid with no Ca2+. My prediction was correct because calcium needs to be present in order for the exocytosis of the synaptic vesicles to work. The exocytosis of the synaptic vesicles is dependent upon calcium. 3 What happened to the amount of neurotransmitter release when you switched from the extracellular fluid with no Ca to2+the extracellular fluid with low Ca ? How 2+ well did the results compare with your prediction? Your answer: The amount of neurotransmitter release increased by a little when I switched from the extracellular fluid with no Ca2+ to the extracellular fluid with low Ca2+. My prediction was correct because instead of having 0 neurotransmitter released like in the no Ca2+ solution, 1 synaptic vesicle was released in the low Ca2+ solution during the low intensity stimulation. Therefore, small amount of synaptic vesicles will be released when small amount of calcium are added back into the solution. 4 How did neurotransmitter release in the Mg 2+ extracellular fluid compare to that in the control extracellular fluid? How well did the result compare with your prediction? Your answer: Generally, less neurotransmitter was released in the Mg2+ extracellular fluid in comparison to the control Ca2+ extracellular fluid. My prediction was incorrect because I answered that there will be no neurotransmitter released at all when magnesium is added to the extracellular solution. However during the experiment, at a low intensity stimulation, 1 synaptic vesicle was released in the magnesium solution unlike how 2 vesicles were released in the control Ca2+ fluid. Then at high stimulation, 3 synaptic vesicles were released in the Mg2+ fluid in comparison to how 6 vesicles were released in the control fluid. Therefore, there are some neurotransmitter release in the Mg2+ fluid but the number is lesser than the control extracellular fluid. 5 How does Mg 2+ block the effect of extracellular calcium on neurotransmitter release? Your answer: Extracellular magnesium ions block the effect of extracellular calcium on neurotransmitter release by blocking the calcium channels in the axon terminal, thus inhibiting the exocytosis of neurotransmitter vesicles.