Ion Channels, Resting & Action Potentials Flashcards
Take Homes of Ion Channels Presentation (5)
- Ion Channels = generate ____ membrane potential and action potential
- Nernst Equation = electrochemical _____ potential for an ion across cell membrane
- ______ Equation = steady-state potential for multiple ions across the cell membrane
- Resting membrane potential = ___mV in many neurons bc neurons are primarily permeable to ___
- Action Potential Propagation: Unmyelinated axons = ____ conduction; myelinated axons = _____ conduction
- Ion Channels = generate resting membrane potential and action potential
- Nernst Equation = electrochemical equilibrium potential for an ion across cell membrane
- Goldman-Hodgkin-Katz Equation = steady-state potential for multiple ions across the cell membrane
- Resting membrane potential = -70mV in many neurons bc neurons are primarily permeable to K+
- Action Potential Propagation: Unmyelinated axons = continuous conduction; myelinated axons = saltatory conduction
What are the 3 Gating mechanisms?
- voltage gated
- ligand gated
- mechanical stress gated
Selective ion permeability of voltage gated channels is it which 3 ions?
selective to K+, Na+ or Ca2+
Selective ion permeability of ligand gated channels is cation selective to ___, ___ and sometimes ___ while anion selective to ___.
cation selective K+, Na+, sometimes Ca2+
anion selective Cl-
Channelopathies are
genetic disorders affecting ion channels
What Na+ channel is strongly expressed in nociceptive DRG neurons?
NaV1.7
NaV1.7 mutations cause _____ of DRG neurons and ______
hyperexcitability; neuropathic pain
Nonsense mutations in NaV1.7 result in
complete inability to sense pain (channels not being expressed at all)
Delayed rectifier K+ channels open with ______ and close with ______
depolarization; repolarization
What generates the falling phase of the action potential?
Delayed rectifier K+ channels
What generates the resting membrane potential?
Leakage K+ channels
Leakage K+ channels ____ at the resting membrane potential
open
What channel inactivation (closing after opening) includes a “ball and chain” protein segment that causes inactivation recovery from inactivation only after neuron repolarizes?
Na+
Na+ channel gate ____ with depolarization
open
What channel generates the rising phase of the action potential?
voltage gated Na+
What are the types of Ca2+ channels? (voltage subsets)
- High Voltage
a) L-type
b) N-type - Low Voltage
c) T-type
T/F: In the Ca2+ channels, inactivation time varies based on type
true
L-type ca2+ channels are sensitive to _______ and are a part of excitation-contraction coupling in _____
dihydropyridines; skeletal muscle
N-type ca2+ channels has a transmitter that releases at the
synapses
High voltage activated Ca2+ channels are at a charge of ____ depolarization
-50mV
Low voltage activated Ca2+ channels are at a charge of ____ depolarization
5-10mV
Which 2 ions flow INTO the cell?
Na+ and Cl-
Which 2 ions flow OUT OF the cell?
K+ and A-
Ion gradients across cell membranes are maintained by what enzyme?
Na+/K+ ATPase
What is the natural charge of the intracellular membrane?
-85mV
The equilibrium potential for K+ is
negative
In equilibrium potential, the membrane is permeable to ____ ion
one
In equilibrium potential, the ion flux is driven in _____ direction by the ________ across membrane
one; chemical gradient
In equilibrium potential, flux results in (2)
- charge difference
2. voltage across membrane
In equilibrium potential, opposite ion flux is driven by
the membrane voltage
Electrochemical equilibirum is achieved at the voltage where the 2 fluxes…
balance each other out
What are the equilibrium potentials for K+ and Na+?
K+: -90mV
Na+: +50mV
What equation tells you what the equilibrium potential is?
Nernst Equation
Which leakage channels are ALWAYS open in neurons?
K+
Why is the resting potential -70mV instead of -90mV?
Because other channels like Na+ and Cl- are open which make the resting membrane potential a little more positive than the K+ equilibrium potential
Generation of the action potential is a
all-or-none event
Resting membrane potential
voltage-independent gK; leakage K+ channels
Rising phase
activation of gNa; voltage gated Na+ channels (2)
Falling phase
inactivation of gNa and activation of gK; inactivation of voltage-gated Na+ channels and delayed rectifier K+ channels (3) and leakage K+ channels
Action potential depolarization in one region spreads ______ to neighboring regions
passively
Passive depolarization initiates
action potential in neighboring region
Myelinated axons include nodes of Ranvier which are separated by
long stretches of myelin
Myelin is formed by which glial cells? (2)
oligodendrocytes & Schwann cells
What is the internodal distance of Nodes of Ranvier?
1-2mm
Saltatory Conduction
action potential depolarization at one node spreads passively to neighboring node 1-2mm distance; rapid propagation velocity
Equilibrium potential equation
Vion (mV) = 58/z x log x {ion}0/{ion}i
log(10) = 1
log(1) = 0
log (1/10) = -1
Na+ equilibrium is ____ if there is a higher concentration of Na+ outside the cell than in
positive
Why is it more difficult to generate a 2nd action potential immediately following the generation of an action potential?
- Na+ channels are inactivated and cannot open to depolarize the neuron
- Delayed rectifier K+ channels remain open, hyperpolarizing the cell
What will happen to an action potential traveling down a myelinated axon when it encounters a demyelinated region of the axon?
block/slowing of action potential
example: Multiple Sclerosis
