Exam 2 - Lecture 20 (Membrane Potential 1) Flashcards
What is the RMP? (definition and number)
Potential difference across the membrane; net charge on the inside of the plasma membrane compared to the outside.
-65 mV
What does the Goldman equation calculate?
The membrane potential
Which side of the cell is NORMALLY negative?
inside
What does the RMP reflect?
Uneven distribution of ions across the plasma membrane by the electrochemical gradients of the Na/K pump, selective ions, and large intracellular ions that cannot leave the cell.
What is another name for the Na/K pump?
ATPase pump
At what rate does the Na/K pump work?
continuously
What ions are selectively permeable to the membrane?
K, Cl, Na
What type of channels do K and Cl use?
Nongated (leak) channels
How does Na get into the cell?
We are not sure
What is important about the large intracellular ions of the cell?
They are too large to exit and are negatively charged (anions), so contribute to negative charge of the inside of the cell
Which way does K move across the membrane?
In; cannot move out
What happens when electrical force inside of the cell equals the diffusional force outside of the cell?
No ions diffuse into or out of the cell
What is depolarization?
Decrease in potential difference across the plasma membrane, going to more positive, approaching 0 mV.
What is overshoot?
Potential difference > 0mV
What is repolarization?
Return of the membrane to its normal RMP.
What is hyperpolarization?
Increase in potential difference across the PM, going to more negative, away from the RMP
What are the 2 steps by which a sensory receptor transduces a signal (aka converts sensory stimulus to electrical signal)?
- Sensory stimulus generates receptor potential
2. Receptor potential leads to AP
What are the 2 ways by which a sensory stimulus generates receptor potential?
- Opens specific ion channels
2. Opening of channels leads to depolarization and hyperpolarization of receptor membrane
What 3 specific ion channels are opened when a sensory stimulus occurs?
- Mechano-gated Na+ channels
- Heat-gated Na+ channels
- Cold-gated Na+ channels
What is a potential produced by sensory transduction?
A depolarizing event resulting from inward current flow
What is receptor potential?
Depolarizing potential of receptor membrane
What happens to electrical potential across the plasma membrane for a brief period when the receptor potential is generated?
Brief reversal in electrical potential
What happens during the brief reversal in electrical potential once a stimulus occurs?
Inside of the cell is positive, outside of the cell is negative
When is an AP generated?
When the receptor potential goes over the threshold potential
What is the threshold potential?
-55 mV
What 2 things does the generation of an AP require?
- Voltage-gated Na+ channels
2. Voltage-gated K+ channels
Does the sensory receptor itself have any voltage gated channels?
No; it only has mechano-, heat- and cold-gated
What are the 3 cycles that the VG Na+ channel goes through during an AP and what happens during each?
- Resting - channel closed
- Activated - channel open
- Inactivated - channel closed
When does Na+ cross the membrane? (During which VG Na+ channel cycle?)
Only crosses during activated state (channels open)
What must happen to inactivated Na+ channels before they can open again?
They must be de-inactivated to the resting state
What channels open when the receptor potential goes over threshold and at what rates?
ALL VG Na+ (rapid) and K+ channels (slowly)
What happens when Na+ channels rapidly open?
Na+ influx, then stop
What happens when K+ channels slowly open?
K+ outflux, then stop
What happens to Cl influx vs. outflux during an AP?
Does not really move in or out
