Lecture 4: Graded Potentials & Action Potentials Flashcards
1. Describe a graded potential 2. State how stimulus polarity and magnitude affect a graded potential. 3. Define spatial and temporal summation of graded potentials. 4. List the sequence of membrane permeability changes responsible for an action potential. 5. Define absolute and relative refractory periods. 6. Describe how some anesthetics can block nerve activity.
What is a graded potential?
A graded potential is a + or - change from the resting membrane potential. It is DEPENDENT on the initial stimulus magnitude (smaller stimulus means smaller depolarization). This stimulus decrements over time and distance. A graded potential can summate with other stimuli in time and space.
When a graded potential exceeds over the threshold it produces a(n) ______________?
Action potential
what makes a graded potential travel?
the opposite charges from the depolarizatizing stimulus travels along the membrane until the charge dissapates to electroneutrality
When the threshold for an action potential is reached how are the voltage-gated sodium channels affected?
At resting membrane potentials, the Na channel is usually closed (keeping Na+ out). As the threshold is reached and an action potential produced, some of the Na channels open, allowing Na to flow in further depolarizing the membrane. More depolarizing means more channels opening until all or most of them are open (regeneration). At this point the membrane potential reaches near the Na equilibrium potential bc of the high membrane permeability relative to K
How does the membrane recover from an action potential in a Na/K channel?
The action potential is reached when the membrane potential meets the threshold. At the threshold enough Na channels are open to cause a great influx in Na further depolarizing the system and opening all Na channels. To return to normalcy, the protein blocking the K+ channel moves in response to the vast positive charge and inactivates the Na+ channels at the same time, thus decreasing Na+ permeability and allowing K+ to exit the cell. thus allowing the membrane potential to return to rest or a hyperpolarized state.
T/F. A second stimulus can occur during or right after an action potential.
FALSOOO!! No action potential can be reached when the sodium channels are inactivated. The time right after an action potential is called the ABSOLUTE REFRACTORY PERIOD! it can take several times longer for membrane potential to reset than it did for the action potential to occur.
it takes a lot of time to recover from being drunk than it takes TO get drunk.. let that marinate for a second.
How does a relative refractory period differ from an absolute refractory period?
During an absolute refractory period, no action potential can occur.. the sodium channels are out of commission. During a relative refractory period, however, some channels have reset so an action potential can occur BUT the threshold stimulus needed is greater. (it’ll take a lot more effort to get me to come out the night after i was obliterated but if you wait long enough me and the membrane potential will return to normal threshold levels)
What kinds of stimuli can cause threshold depolarization?
- voltage-gated changes in membrane permeability
- ligand-gated changes in membrane permeability
- inhibited by hyperpolarizing changes in membrane permeabiliy
How do anesthetics affect membrane potentials?
Anesthetics block the opening of Na channels preventing a flux of Na it enter the cell thereby inhibiting a threshold stimulus for an action potential to be reached.
