Hayley - WEEK 4 key - TA Hayley Cliatt [email protected]

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TA: Hayley Cliatt Section: Wed 1-1:50 pm @ HSS 2150 [email protected] OH: Fri 3-4 pm @ PC Theatre Lobby BIPN100 WEEK 4 WORKSHEET TOPICS COVERED: - Voltage clamp experiment - Conduction of Action Potentials - Synaptic Transmission - Ionotropic + Metabotropic Receptors - Postsynaptic Potentials: EPSPs + IPSPs - Long Term Potentiation 1. VOLTAGE CLAMP EXPERIMENT The voltage clamp experiments conducted in the squid axon were utilized to understand what ions flowed and in which directions they flowed throughout the action potential. (a) Below, draw on a current vs time graph what the researchers saw when the depolarized the axon to 0 mV. Be sure to label which ion is flowing at each point in your graph. (b) Draw how the currents would look if the squid axon was treated with TEA before it was depolarized to 0 mV. Explain why your graph differs from the one in part (a). TEA is toxin that blocks K + channels such that there will only be the initial Na + current inwards, the outwards current would be missing, because K + would not longer be allowed to flow.
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TA: Hayley Cliatt Section: Wed 1-1:50 pm @ HSS 2150 [email protected] OH: Fri 3-4 pm @ PC Theatre Lobby (c) Draw how the currents would look if the squid axon was treated with a TTX before it was depolarized to 0 mV. Explain why your graph appears this way. TTX is a toxin that blocks Na + channels, so Na + will no longer be allowed to flow, thus you will lose the initial inwards current, and only the outward K + current will remain. 2. CONDUCTION OF ACTION POTENTIALS (a) Action potentials, unlike graded potentials do not _ decay _ with distance. This is because the action potential occurring at one point along the axon acts as a(n) _ above threshold stimulus __ to adjacent portions of the axon. The main advantage of this mechanism is that it _ regenerates __ the action potential at each portion along the axon allowing for them to be conducted without __ loss __. (b) What prevents the backwards conduction of action potentials? The refractory period ultimately prevents the backwards conduction of action potentials. Because the previous portion that just underwent an action potential will be in its refractory period when the adjacent portion undergoes its own action potential, the newly generated AP cannot induce an AP in the previous segment. BONUS: Think about what would happen if you stimulate an axon in the middle… (c) Name two ways in which the conduction velocity of axons can be increased and explain the mechanism by which they do so. Conduction velocity can be increased via… (1) Increasing diameter of the axon à from Poiseuille's Law we know that increase the diameter (aka increasing the radius) will drop the resistance which will increase the flow (of the AP) in this case, thereby increasing conduction velocity as well!
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TA: Hayley Cliatt Section: Wed 1-1:50 pm @ HSS 2150 [email protected] OH: Fri 3-4 pm @ PC Theatre Lobby (2) Increasing myelination à
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