Session 5: Action Potentials Flashcards Preview

Sem 1: Pharamacology and Physiology > Session 5: Action Potentials > Flashcards

Flashcards in Session 5: Action Potentials Deck (27):

What is an action potential?

Change in voltage across a membrane


What is conductance?

The number of channels for the ion that are open.


TRUE OR FALSE: If the conductance to any ion is increased the membrane potential will move closer to the equilibrium potential for that ion.



Which ion is responsible for AP depolarisation?



How can it be experimentally proven that sodium is the ion responsible for AP depolarisation?

The peak of the action potential changes in a parallel manner to the changes in the equilibrium potential for a sodium ion.


What is membrane capacitance?

The ability to store charge and determines how quickly the membrane potential can respond to a change in current.


Why are voltage clamps useful?

They allow a membrane current to be measured at a set membrane potential


What is the role of the Na/K pump in an AP?

Helps maintain the cells resting potential. (Not involved in the repolarisation!!!!!)


Define absolute refractory period.

Regardless of how strong a stimulus is no AP can be achieved.


Define relative refractory period.

A very strong stimulus has to potential to initiate a new AP


What is meant by inactivated sodium channels?

The are blocked by an inactivation particle so ions can now longer flow through the channel. They will only recover once the cell has become hyperpolarised (more negative). Hence, until this happens no new AP can fire.


Describe the molecular chemistry of a sodium channel.

- 1 subunit (single polypeptide)
- S4 voltage sensor (abundant positive charge)
- 4 alpha helical regions
- Pore


What does the abundant positive charge on the S4 voltage sensor allow to happen?

Creates a voltage field across the membrane therefore causing a conformational change, hence opening the pore to allow ions through.


Describe the molecular chemistry of a potassium channel.

- 4 subunits
- S4 voltage sensor (abundant positive charge)
- pore


Describe local current theory.

Sodium moves into the cell causing positive charges to repel one another and negative changes to be attracted to the positive charge.

This causes depolarisation of adjacent areas.

The impact is smaller the further from the initial area of depolarisation.


What is meant by the length constant?

The distance it takes for the potential to fall to 37% of its original value.


What is the membrane resistance dependant on?

The number of ion channels open.


What is the capacitance dependant on?

The property of the lipid bilayer.


What is the result of a cell with a high capacitance?

Voltage changes more slowly in response to a current injection.


What is the result of a cell with a high resistance?

change in voltage spreads further along the axon.


Which cells are involved in myelination?

Schwann cells (peripheral nervous system)
Oligodenrocytes (CNS)


What is saltatory conduction?

When the action potential jumps from node to node


What property of myelin sheath makes it good for saltatory conduction?

Good insulator


Name a demyelinating disease.

Multiple Sclerosis


Describe a positive feedback loop associated with AP.

The opening of many voltage-gated sodium channels causes the cell to become less negative, causing yet further sodium voltage-gated channels to open.


What causes the rapid upstroke of the AP?

The rapid influx of sodium ions


What 2 things does depolarisation cause?

1. Inactivation of sodium channels
2 Opening of voltage-gated potassium channels