Nervous System Physiology

Question 1

What are Resting Membrane Potentials?

Answer 1

Measured when neuron is inactive, about -70mV due to the unequal distribution of ions across the membrane.

Question 2

What concentration of Na+ and K+ does extracellular fluid always have?

Answer 2

High concentration levels of sodium, low concentration levels of potassium.

Question 3

What concentration of Na+ and K+ does intracellular fluid have?

Answer 3

High concentration levels of potassium, low concentration levels of sodium.

Question 4

What is the Sodium Potassium Pump?

Answer 4

An ATP-fueled channel that works against the concentration gradient to move 3 sodium ions out of the cell and 2 potassium in.

Question 5

When is the Potassium leak channel open?

Answer 5

At rest, potassium leaks out of the cell. 50x more potassium leak channels than sodium leak channels.

Question 6

When is the voltage-gated sodium channel closed?

Answer 6

At rest and during repolarization.

Question 7

When is the voltage-gated potassium channel closed?

Answer 7

At rest.

Question 8

When is the Sodium leak channel open?

Answer 8

At rest, sodium leaks into the cell.

Question 9

Where does the -70mV come from?

Answer 9

-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.

Question 10

What does it mean for the cell to be polarized?

Answer 10

It means the cell is negative inside.

Question 11

What is Depolarization?

Answer 11

When the cell membrane goes from negative to positive.

Question 12

What is Hyperpolarization?

Answer 12

When the cell membrane gets more negative (drops further from -70mV).

Question 13

What is the Threshold Potential?

Answer 13

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)

Question 14

What are Action Potentials?

Answer 14

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.

Question 15

What are the special features of action potentials?

Answer 15

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.

Question 16

At what point do the sodium voltage-gated channels open?

Answer 16

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.

Question 17

What happens when the membrane reaches +35mV?

Answer 17

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.

Question 18

What is the Refractory Period?

Answer 18

The time where sodium channels are inactivated while potassium channels are activated, ensuring that the current/action potential moves only in one direction.

Question 19

The ___ of Action Potentials can change but not the ___ of the Action Potentials.

Answer 19

Frequency, size/magnitude.