BSI Lecture 54 Basic Electrophysiology 2 Flashcards
In a “resting” neuron the resting membrane potential, (RMP), is determined by _____ and _____ _____ channels, (plus a small hyperpolarizing contribution by the electrogenic Na+-K+-ATP’ase pump): these are the only channels open in the resting state
Na+ ;K+ ; leak
The Na+ equilibrium potential is _____ mV while that for K+ is _____ mV
~ + 60; ~ - 90
The RMP (~-60mV) is principally determined by the relative contributions of the two types of ______ _______
leak channel
There are actually far more ____ leak channels than ____ so the RMP is biased strongly towards the ___ equilibrium potential, (~-90mV), at around -60 mV.
K+ ; Na+; K+
Leak channels can be modulated by various ______ and ________ messengers, chemicals, etc. which can affect the _____.
endogenous; exogenous; RMP
T or F? If the neuron becomes more positive, (closer to “threshold” when voltage-gated channels will open), the neuron will be more “excitable;” if more negative, (away from threshold), the neuron will be less excitable
True
T or F? ALL neurons will stay at the RMP until “stimulated” via synaptic inputs
False, some neurons, (or even specialized cardiomyocytes), are “pacemakers” and need to fire spontaneously/automatically: these cells have an unstable RMP with leak channels whose conductance changes so the Em constantly decreases/depolarizes towards the threshold.
When depolarization occurs and does not reach threshold, does an AP occur?
No
If a neuron is already firing and depolarization occurs, what happens to the AP?
It’s firing rate will increase
T or F? Hyperpolarization will create an AP?
False, hyperpolarization causes a decrease in Em not increase.
Many neurons are rarely/never at “rest” but are always generating APs: will ________ increase the rate of AP generation while will reduce or stop it.
depolarizing/hyperpolarizing
When reaching threshold, which voltage-gated channel opens quicker, Na+ or K+?
Na+
T/F: Voltage-gated, (VG), channels have voltage sensors that open and close the pore:
True
T or F? vgNa+ channels usually have a second, inactivation gate that automatically closes to prevent excessive depolarization that can be harmful to the neuron
True, (positive feedback followed by negative feedback: but some vgK+ channels inactivate also).
T or F? Once threshold is reached vgNa+ channels open very fast causing the Em to rush towards the Na+ equilibrium potential eventually reaching Na+ equilibrium.
False, this rapid depolarization “overshoots” typically to around + 30 mV but never reaches the Na+ equilibrium potential because of the automatic closing of the channels by the inactivation gate.
The opening of vgNa+ channels is a rare example of _____ feedback: the more/faster the neuron depolarizes to and above threshold, the more vgNa+ channels open so increasing the depolarization:
positive; (inactivation stops this process by separate, negative feedback, (separate mechanism: see homeostasis)
What causes the repolarization after the vgNa+ channels have opened?
The opening of the vgK+ channel
The vgK+ channels start to close at threshold but slowly so the Em nearly reaches the K+ equilibrium potential and then slowly returns to the RMP assuming there are no further stimuli: this is the ________
after hyperpolarization
This afterhyperpolarization is essential as this removes the vgNa+ channel inactivation, why must this occur?
Must occur before another AP can be generated: this ensures that each AP is a complete and separate event, (the “neural code” is preserved).
If the depolarizing stimulus, (or even a new one), that caused the neuron to fire initially was strong and prolonged then, following the afterhyperpolarization, where would the Em be at?
The Em will immediately return to threshold, (after the vgK+ channels have closed), and another AP will be generated: stimulus intensity is coded by the number of APs.
What is absolute refractory period?
During the period of repolarization, before the vgNa+ channels inactivation has been removed, the neuron cannot fire another AP.
T or F? APs are “all-or-nothing” events: once threshold is reached you get a whole AP generated.
True
What is the only information that neuron’s carry?
In a particular neuron all APs are very similar, if not identical, in amplitude, (mV), duration, (~ 1 ms), and are propagated at the same rate: therefore the only information they can carry is in the number of APs.
The initial segment is refractory after the generation of the AP so it can only be regenerated _______ from the cell body down the axon: this is normal, orthodromic AP transmission.
away