Electrical Signaling Flashcards
Why is the membrane potential close to the Nernst potential of K+?
The membrane is much more permeable to K+ therefore the strong gradient that K+ has is what determines membrane potential. Na+ is not as permeable and is similar to the action potential.
What conditions create the RMP?
- intracellular concentration of K+ is much higher than extracellular.
- K+ ions diffuse freely in both directions due to K+ leak channels
- Na+/K+ pumps are pumping K+ into cytosol and maintaining intracellular K+ at 140 mM
- extracellular K+ is maintained at 5 mM by kidneys
What are VGNCs and what are the three distinct states of being they can be in?
Voltage Gated Sodium Channels.
- closed and ready to open
- open and conducting Na+ ions
- inactivated, similar to open but nonconducting.
What to Voltage sensing S4 segments do?
S4 segments are positively charged parts of the VGNCs and they can change the state of the channel. S4 is positively charged and therefore will be on the negatively charged side of the membrane (which changes during polarization). movement of the S4 toward extracellular space results in opening the channel’s pore and allowing Na in.
How do ion channels select for ions?
Ions are surrounded by spheres of hydration which must be removed to enter the channel. The selectivity loops are precisely spaced charged parts of the channel pore that can substitute exactly for water molecules and allow the ion in. the precise spacing allows for only one type of ion to have water substituted.
What is a technique for recording ion flow through individual ion channels?
inside-out, detached patch recording. This technique pinches a single ion channel and removes it from the membrane for study. voltage is applied to depolarize the channel, channel openings are stochastic so aggregates are used to show average current flow over many trials.
what effect does lowering external Na+ concentration have on action potentials?
it reduces the electrochemical driving force and lowers the Nernst potential. This makes the peak of the AP occur at less positive voltages with lower extracellular [Na+]
What is the probability of an action potential occurring at the threshold potential?
Only 50% probability of an AP being triggered. We want higher probability so that is why cells contain 1000s of channels, not all of them must open to create an AP.
What does Non-decrementing propagation of action potentials mean?
the amplitude of the waveform does not decrease as the AP propagates along the axon. this indicates that the AP is being created as it propgates
How is AP propagation unidirectional?
the fast, spontaneous inactivation of VGNCs prevents the AP from reversing direction. Channels in front of AP are closed and ready to open, channels behind are inactivated and cannot allow sodium passage
How do Local Anesthetics work? give some examples
LA’s block pain by blocking VGNCs in sensory neurons. includes procain, lidocaine, and cocaine.
what does tetrodotoxin do?
Tetrodotoxin blocks voltage gated Na+ channels by plugging the extracellular mouth of the pore. it is found in pufferfish, porcupine, blue-ringed octopus, and rough-skinned newts
what is Saxitoxin?
saxitoxin is similar to tetrodotoxin as it blocks VGNCs. it leads to paralytic shellfish poisoning
What is Brevetoxin?
a toxin that binds to VGNCs and produces a lowering of activation potentials and persistent activation of the channel and the inability to reverse the prolonged open state.
What is myelination and what cells are responsible for it?
myelination increases AP conduction velocity and renders conduction saltatory, reducing energy expenditure. Schwann Cells (glia) form myelin sheaths
