Voltage Dependent Membrane Permeability Flashcards
Which way does current flow across the membrane during the rising phase of the action potential?
Inward current
Which way does current flow across the membrane during the falling phase?
Outward current
How will the action potential be affected if you remove Na+ from the external medium?
Action potential will gradually get smaller in amplitude as the Na+ in the external environment decreases until the Na+ starts to leave the cell instead of entering which no longer produces an action potential
How will the action potential be affected if you remove external K+?
The amplitude of the action potential will not be affected in anyway. Even if the external K+ is removed, the inside of the cell still has a higher concentration, making the action potential normal
How does the voltage sensitivity of K+ conductance contribute to the action potential?
Voltage sensitivity of the K+ conductance contributes to the falling phase of the action potential to prevent the potential from remaining excited at all times,
Do unmyelinated axons carry action potentials?
YES! but is it extremely slow in comparion to myelinated axons
What is the purpose of myelin?
Myelin is responsible for speeding up the action potential transmission.
Explain how myelin speeds the conduction of the action potential.
Myelin is a fatty sheath that insulates the axons. With these insulators, no current will leave the axons, retaining the current inside the axons to move via passive flow to the nodes of Ranvier where there are exposed membranes with localized ion channels for action potentials.
What prevents action potentials from turning around and going back up the axon?
Refractory period
There is Na+ channel inactivation that prevents the Na+ channels from causing another depolarizing event immediately. There is also a longer K+ activation period, making it difficult for depolarization again.
What is the voltage clamp?
A device that can control the membrane potential to be an any voltage desired by the experimenter.
Regenerative properties of the action potential
Positive feedback loop: Activate voltage gated Na+ channels -> Na+ entry -> depolarization -> activation more more Na+ -> more Na+ entry -> more depolarization
Using the voltage clamp, what happens to the current when the membrane is hyperpolarized?
Nothing special happens
Using the voltage clamp, what happens to the cuurent when the membrane is depolarized?
There is an initial transient inward current and then a delayed outward current.
How do we know that Na+ is resposible for the early current flow?
There is no current flow when the membrane potential is clamped at around +52mV which is around the predicted equilibrium potential of the Na+.
How does tetrodotoxin and tetra-ethylammonium provide evidence for two distinct mechanisms for action potentials?
Tetrodotoxin blocks Na+ current without affecting K+ current. Tetra-ethylammonium block K+ currents without affecting Na+ currents.
The differential sensitivity provides shows that they are two independent pathways.
What is membrane conductance?
Reciprocal of membrane resistance
What is membrane resistance?
The ability of the membrane to allow charges to move in and out of the cell
What is axial resistance?
The ability of charge to travel trhough the cytoplasm
What is membrane capacitance (Cm)
The ability to store charge
What is unique to Na+ conductance that is not in K+ conductance?
Over time, the depolarization also causes Na+ channel inactivation (not closing) but not in K+ channels/conductance
How does the ion channel dependence on time affect action potential?
Na+ conductance activates more rapidly while the K+ has a more dlayed activation which allows the action potential to quickly hit its peak and then the K+ will create the falling phase
How does voltage affect the Ion conductivity?
As the neuron is depolarized, the conductances is increased progressively
How do action potential propagate in long distances?
The passive properties will allow some of the local curretn from an action potential to flow down the axon, depolarizing the membrane in the adjacent region.
If the length constant of a neuron is high, it means
that a charge can travel further down the process without decaying
