# week 3-4 - Question from Practice Midterm What`s a way for...

• Test Prep
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Question from Practice Midterm

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What`s a way for calculating the driving force? Ohm`s Law What`s a way for converting the electrical driving force to chemical driving force? Nernst Equation
Question What if it transports 1 Ca++ and 2Na+ instead of 1 Na+ and 1 H+? What would be the chemical gradient established for Ca++

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Voltage Clamp Continued

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Drugs Tetrodotoxin (TTX) Blocks Na+ channels Reduce inward currents Tetraethylammonium (TEA) Blocks K+ channels Reduce outward currents
Why would we want to add drugs to the solution while doing the voltage clamp experiment? The currents that we observe after voltage-clamping the squid axon are a combination of Na+ and K+ currents. Applying those drugs can help us to observe these two types of currents separately. After applying TTX---only K+ current would be observed After applying TEA---only Na+ current would be observed

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Voltage clamp after applying TTX The current observed is an outward potassium current. Which channels contribute to the potassium currents observed?
Voltage clamp after applying TEA The current observed is an inward sodium current. Which channels contribute to the sodium currents observed? Adding the Na+ and K+ current together one can get the total current.

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Question What would happen to the K+ current during voltage clamp observed if one increases the extracellular K+ concentration?
Answer Less outward K+ current + decreased amplitude Think of Ohm`s Law Magnitude of current is proportional to the driving force and conductance

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Question from practice midterm.
What happens before an action potential is transmitted? Stimulants binding to receptors changes membrane permeability to certain ion species, resulting in changes in membrane potentials of afferent neurons.

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Signals integrate at trigger zone (axon hillock) What tells the difference between a strong stimulus and a weak stimulus?
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• Fall '07
• French
• NMDA, frequency stimulus, Low frequency stimulus, high frequency stimulus

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