Flavia’s quiz on neurons

QUESTIONS:

· what is the membrane for?

à separating charge, so that during depolarization, an action potential can be generated

· Why is the action potential useful in signaling?

à (long-distance communication)

· what is the sodium potassium pump?

à it is a protein that moves 3 Na+ ions out of the cell and moves in 2 K+ ions – i.e. against their concentration gradient

· what happens to the membrane/input resistance of a neuron if you increase the size of a neuron?

à you are decreasing the input resistance, because there are more resting channels to conduct ions, i.e. current can flow into the neuron more easily

· What is the reversal/Nernst potential? What is the Nernst potential for K+, Na+, Cl-?

= the potential at which the electrical forces acting on an ion exactly balance the chemical (diffusional) forces acting on it

- E _K+ = -75 mV; E _Na+ = +55 mV, E _Cl- = -60 mV

· What happens to the capacitance of a neuron if you increase its surface area? (bigger neuron)?

à capacitance goes up

· How does an increase/decrease in capacitance affect the speed of current conduction?

à increase in capacitance slows down current conduction.

· what is capacitance good for in the context of electrical signaling in neurons?

à it leads to temporal summation of EPSPs

· For purposes of fast signal conduction, what sort of axons are the most useful?

à large, myelinated ones

· how does myelin affect the conduction of electrical signals (current)?

à i) it decreases the capacitance, thereby speeds up conduction

à ii) it creates greater membrane resistance, thereby leading to less leaking of current, and thereby increasing the current’s length constant (1/e)

· how does a larger axon/dendrite diameter affect current flow?

à the larger the diameter of the cytoplasmic core, the lower the resistance in any given length, because the number of charge carriers (ions) increases with the diameter of the dendrite core

· Is the resistance of the extracellular fluid (outside the cell) large or small?

à negligible, because of its large volume

· Which parts of the neuron have resistance (i.e. what are the types of resistance current flow encounters in a neuron?)

à Resistance: 1) axial 2) membrane

· What happens if we put a bunch of potassium outside a cell when the cell is at a resting potential?

à it should lead to an influx of potassium into the cell, because the electrostatic positive force outside the cell will surpass the electrochemical force trying to push K+ out of the cell

· What do the resistors correspond to in a membrane?

à channels – mainly; although note that there is resistive current flow through the membrane even if the channels are closed; the membrane is leaky

· What does the capacitor correspond to in a membrane?

à a patch of the lipid bilayer (i.e. a patch of the membrane) without holes/channels

Might need to know the Nernst equation to calculate stuff on tests