Ch.3 Voltage Dependent Membrane Permeability

the action potential (the membrane)

• reflects changes in membrane permeability to specific ions

• increase in Na+ initiates the action potential

the voltage clamp method (what it is)

• clamps the membrane potential to a given voltage level

• shows how the membrane potential can influence ionic current flow across the membrane

the voltage clamp method (steps)

1) recording electrode measures the cell’s current electrical charge

2) a command voltage is set (the target value)

3) the voltage clamp amplifier compares the membrane potential to the command voltage

4) the voltage clamp amplifier will pump electrical current into and out of the cell if the cell does not match the command voltage

• forces the machine to stay at a fixed charge

• these changes in voltage can determine the electrical activity of the ion channels

inward charge means? (squid axon membrane)

positive charge entering the cell, deflects down on graph

outward charge means (squid axon membrane)

negative charge entering the cell, deflects up on graph

what is capacitative current?

the movement of ions based on the charge injected

what is reversal potential?

flow of ions through a channel changes direction

once a neuron is depolarized, Na+ channels are the first to open and rush into the cell (true or false)?

true

Na+ cannot change direction based on how high the voltage is (true or false)

false

a slower K+ can become stronger when the cell is more depolarized (true or false)

true

when Na+ is not present in the cell, the cell expels other materials outward, not inward (true or false)?

true

what is tetrodoxin (TTX)?

• blocks Na+ channels

• forces the cell to not move Na+ ions into the cell

what is tetraethylammonium (TEA)?

• K+ channel blocker

• forces the cell to keep K+ inside the membrane

Na+ opens slowly at high voltage and closes slowly at high voltage (true or false)?

False

K+ generally opens slowly at high voltage and closes slowly at low voltage (true or false)?

true

when Na+ enters the cell, voltage increases and vice versa? (true or false)

true

the membrane is not perfect, charge can flow in both directions (true or false)

true

increasing the diameter of an axon, decreases resistance to passive current and increases AP (true or false)?

true

what is saltatory conduction?

voltage travelled by myelinated axons

what are the pros of saltatory conduction?

• myelination increases the speed of an AP

• localizes axons to be close to nodes of ranvier

• higher firing frequency

• saves metabolic energy because the Na+/K+ pumps are on the nodes of ranvier

what are the cons of saltatory conduction?

• myelin sheaths are expensive to make

• myelin degradation risks

• myelinated fibers take up a lot of space on the neuron

unmyelinated vs myelinated axons (how do they compare)?

• myelinated

• -travel faster as the current is injected at one node, passes through myelin, and is driving an AP at each node of ranvier

• unmyelinated

• -travels slower because the current has to be regenerated at every spot of the cell and an AP simultaneously