Physiology Unit 2 Ion Channels

How is the cytoplasm charged compared to its extracellular environment?

the cytoplasm is negatively charged

What is the charge of the cytoplasm?

-70mV

What organelles (large anions) contribute to the negative charge in the cytoplasm?

DNA, RNA, and proteins

Is the membrane potential the same across the entire membrane?

No, the potential varies across the membrane

What causes the differences in charges across the cell membrane?

changing ion concentrations

Which side of the cell membrane does Na+ start on?

the outside

Which side of the cell membrane does K+ start on?

the inside

What maintains the RMP?

the Na+/K+ pump

What is the exchange of Na+ and K+ ions in the Na+/K+ pump?

3 Na+ ions transported out for every 2 K+ ions transported in

What percent of the energy supply to the brain does the Na+/K+ pump use?

60%-80%

What is excitability?

the ability to produce and conduct changes in membrane potential

Which types of cells is excitability unique to?

muscle cells and neurons

What happens to the cell during depolarization?

the cell becomes more positively charged than the RMP

During depolarization, what is happening with exchange within the membrane?

there is an influx of cations

What does depolarization result in?

activation of a nerve impulse (excitatory)

How does the cell change during hyperpolarization?

the cell becomes more negatively charged than the RMP

What is happening with exchange in the membrane during hyperpolarization?

there is an eflux of cations

What does hyperpolarization result in?

the inhibition of a nerve impulse

What is happening with the RMP during repolarization?

the RMP is returning to normal levels

What mechanism is used to return the RMP to its normal levels

the Na+/K+ pump

What is the electrical way ions flow down the electrochemical gradient?

ions go to other ions with opposite charges

What is the chemical way ions flow down the electrochemical gradient?

ions flow from areas of high concentration to low concentration

Where are ion channels primarily located?

axons

Is a sodium ion channel a voltage gated or ligand gated channel?

voltage gated

What 3 conformations does the sodium ion channel have?

closed, open, and inactive

What causes the sodium ion channel to change from closed to open?

a charge of -55mV

What causes the sodium ion channel to change from open to inactive?

a charge of +30mV

What causes the sodium ion channel to change from inactive to closed?

a charge of -70mV

What must happen in order for a sodium ion channel to be re-opened after it has been deactivated?

it must first close and then be re-opened after it is returned to RMP

When do potassium leakage channels open?

random times

Are potassium ion channels open or closed at RMP

closed

What conformations does the potassium ion channel have?

open and closed

At what charge does a conformational change to open the potassium ion channel occur?

+30mV

At what charge does a potassium ion channel undergo a conformational change to close?

-90mV

At what point does a stimulus depolarize a cell membrane?

when the charge is below -55mV