Flashcards in Nervous System Physiology Deck (19):
What are Resting Membrane Potentials?
Measured when neuron is inactive, about -70mV due to the unequal distribution of ions across the membrane.
What concentration of Na+ and K+ does extracellular fluid always have?
High concentration levels of sodium, low concentration levels of potassium.
What concentration of Na+ and K+ does intracellular fluid have?
High concentration levels of potassium, low concentration levels of sodium.
What is the Sodium Potassium Pump?
An ATP-fueled channel that works against the concentration gradient to move 3 sodium ions out of the cell and 2 potassium in.
When is the Potassium leak channel open?
At rest, potassium leaks out of the cell. 50x more potassium leak channels than sodium leak channels.
When is the voltage-gated sodium channel closed?
At rest and during repolarization.
When is the voltage-gated potassium channel closed?
When is the Sodium leak channel open?
At rest, sodium leaks into the cell.
Where does the -70mV come from?
-10mV comes from the Electrogenic pump and -5mV comes from anionic proteins. The other -55mV comes from the passive diffusion of K+ through open k+ leak channels.
What does it mean for the cell to be polarized?
It means the cell is negative inside.
What is Depolarization?
When the cell membrane goes from negative to positive.
What is Hyperpolarization?
When the cell membrane gets more negative (drops further from -70mV).
What is the Threshold Potential?
The critical level at which the membrane potential must be depolarized in order to initiate an action potential. Can be reached by one strong stimulus or multiple small ones in fast succession. (-50mV)
What are Action Potentials?
They are initiated at the Axon Hillock, in the Spike Initiation zone, and only found in axons. They carry the signal from the axon hillock to the terminals.
What are the special features of action potentials?
They depolarize the membrane (-70mV to +35mV), "all or nothing", once initiated it cannot be stopped, the size of the spike is always the same. They rely on ion currents through membrane voltage-gate ion channels.
At what point do the sodium voltage-gated channels open?
When the graded potential reaches -50mV (threshold), both the activation and the inactivation gate open - leading to a rush of sodium ions leaving the cell.
What happens when the membrane reaches +35mV?
The inactivation gate of the sodium channel will close and the potassium channel activation gates will open, letting the positive potassium ions leave the cell.
What is the Refractory Period?
The time where sodium channels are inactivated while potassium channels are activated, ensuring that the current/action potential moves only in one direction.