Week 3 Review Flashcards
define excitability as it relates to cells
-having ability to go from RMP (-70mV), have a sudden change, then back to RMP
how does excitability relate to nervous tissue
- excitability = cell’s ability to generate a signal -pain, retinas, sense of smell/taste
- losing your sense of smell/taste is an example of a loss of excitability
Explain the difference between the resting membrane potential and the equilibrium potential of K+ in a nerve cell
-Equilibrium potential of K is established b/w conc gradient (inward) and electrical gradient (outward) and with it an electrical potential -maintain equilibrium inside and outside cell -K channels leaking so inside stays more negative than outside (-90 mV) -RMP = membrane potential of a cell that is stable; no net flux of movement (-70 mV)
Explain how the electrochemical gradient defines the equilibrium potential of K+
-K equilibrium potential is established when inward K movement = outward K movement, so net flux = 0. -This potential represents balance b/w the effects of conc gradients and electrical gradients, resulting in an electrochemical gradient
If the concentration of a positive ion is 10 fold greater inside than outside a cell, and the membrane is slightly permeable to that ion, will the resulting RMP become more positive or more negative over time?
-more negative -the positive ion will want to move down its conc gradient, so it will go outside the cell, resulting in a more negatively charged intracellular space at RMP
If the concentration of a negative ion is 10 fold greater inside than outside a cell, and the membrane is slightly permeable to that negative ion, is the resulting RMP more positive or negative?
-more positive -the negative ion will want to move down its conc gradient, so it will go outside the cell, resulting in a more positively charged intracellular space at RMP
Briefly explain what the Nernst equation allows us to calculate
-electrochemical equilibrium in the cell -helps us determine RMP
define resting membrane potential (RMP)
the membrane potential of a cell that is stable (not producing an impulse)
factors that influence RMP
-ratio of the conc of ions on either side of the membrane -specific permeability of the membrane to each ion -resulting electrical properties inside and outside of the cell
define threshold potential
-baseline needed in order to initiate an action potential -“all or nothing” -has to become less negative/more positive
define depolarization
-occurs when Na channels open up and Na starts entering cell -peak value is when Na equilibrium potential is reached -no further change in amount of Na entering cell
define repolarization
-occurs when Na channels close and K channels open -inside of cell becomes more negative -K moves out of cell, down chemical gradient -goal = return cell to its RMP
define hyperpolarization
-overshoot RMP then rising back to RMP -due to some K+ channels remaining open while the rest of the channels are closing (leakiness) -hyperpolarized cell is more negative and has greater difficulty reaching threshold potential again
Explain the sequence of events that occur over the course of a complete action potential. Explain the sequence in terms of ion movement and open/closed channels.
Explain why nerve depolarization is a positive feedback loop and repolarization of the same cell is a negative feedback loop.
- depolarization = sodium channels open, Na enters cell, more channels open
- repolarization = sodium channels close, potassium channels open
Explain the All-or-None phenomenon as it relates to an action potential occurring in nerves.
- A cell has to reach its threshold potential in order for it to initiate depolarization
- If it does not reach this threshold, it will not activate an action potential
Why does a sushi chef serving you the liver of a pufferfish hold your life in his very hands? Why is lidocaine an effective local anesthetic?
- puffer fish has a toxin that blocks sodium channels that causes your heart to stop
- lidocaine blocks sodium channels as well (locally)
- can be injected in heart to control defective AP
- limits Na channels from opening by blocking the transmission of their signals, so limits pain signals
Why do action potentials not decrease in magnitude with transmission? What would happen if they did?
- the propagation of an AP is an all or none effect
- If there was a decrease in magnitude it would no longer travel down the axon
- AP strength can potentially decline, however, if traveling over a long distance
- myelin sheath is critical in preserving AP integrity
- demyelination results in abnormalities in AP delivery
- ex: patients with MS
- demyelination results in abnormalities in AP delivery
What would happen if the RMP continuously equaled the threshold potential?
- at threshold potential it would make a signal continuously firing
- there would be no refractory period
- could cause the skeletal muscle to continuously contract
- that’s why there is a refractory period
The magnitude of the peak positive component of an AP approximates the ___________ of Na+ (explain)
- equilibrium potential
- this is when the intracellular conc of Na+ is at its highest
- at this point, no more sodium will flow into the cell
What is the sequence of opening and closings of membrane pores/channels during an AP?
- sodium channels open for Na+, inside of cell
- at end of depolarization, Na+ channels will close
- K channels will be open so that they will go outside of the cell
- K channels slow to close, causing hyperpolarization, making the inside of the cell more negative
- repeats the process going down the axon
Explain afterpolarization or hyperpolarization including an explanation of how it happens.
Afterpolarization/Hyperpolarization: Voltage gated K channels remain open after the potential reaches resting level and are slowly closing causing leakiness of K
Describe a graded potential. What are some characteristics of graded potentials?
- Graded potential = changes in a membrane potential that vary in amplitude, depending on the strength of the stimulus
- Typically found in Dendrites (slide 67)
- Do not have to be all or none
- They are local acting
- An example is smell: when you can maybe smell a little or have a strong smell
- a single graded potential is not strong enough to bring about an actional potential
- if enough receptors are stimulated, enough GP will be generated to meet the threshold potential in order to create a depolarization
While APs are usually unidirectional, describe a situation where that is not the case.
- APs that are not unidirectional; can be bidirectional
- An example of this is hitting your funny bone (Ulnar Nerve) because it can travel up or down your arm
