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Na+ channels contribute to what part of the action potential?
K+ channels contribute to what part of the action potential?
falling and undershoot
What does the transient inward current show? And the delayed outward current?
Opening of the Na+ channels
Do K+ channels inactivate quickly?
No they do not get inactivated.
What does hyperpolarization of a neuron do?
Hyperpolarizing does not cause an action potential to occur.
What does depolarization of a neuron do?
Depolarization causes an increase in membrane potential and cause an transient inward current.
What is an inward current?
Flow of positive charge into the cell is defined as inward current.
What is an outward current (rectifying current)?
if K+ flows out of the cell taking its positive charge with it
In a voltage clamp experiment, flow of positive charge into cell is shown as? In current clamp?
Downward deflections during a voltage clamp experiment. Upward deflections in a current clamp experiment
As the membrane potential approaches threshold, what happens to the channels?
Sodium channels start to open and there is the rising phase
As you approach the threshold, what happens to the ion channels?
Sodium channels close and the potassium channels remain open. The falling phase of the action potential
In an environment where there is no sodium extracellularly what happens to the sodium current?
Sodium current decreases
Tetrodotoxin blocks which ion channel?
. Tetraethylammonium blocks which ion
fast and activatin
Slow and noninactivating
The firing frequency is dependent on what?
the refractory periods
What do neurons conduct?
Where is the electrical impulse initiated?
The electrical impulse is initiated in dendrites, and travels through the cell body, down the axon to the presynaptic terminal.
What are the electrical impulses (action
potentials) a result of?
Impulses (action potentials), are result of coordinated opening or closing of multiple ion channels in the cell membrane that are permeable to Na+, K+, Ca2+, and Cl-.
What are the three types of potentials and are they graded or all or none?
Receptor potential (Graded), Synaptic (Graded), and Action potential (All or none).
Do action potentials grow in amplitude with a larger stimulus?
No, action potentials do not grow with a larger stimulus. Action potentials increase in frequency with a larger stimulus.
What does electricity depend on?
Electricity depends on the flow of ions (charged particles).
What is charge measured in?
Charge is measured in Coulombs (C), where the charge on a single proton (elementary charge) is 1.6 x 10^-19 C.
What is current?
Current is defined as the movement of charge in a given period of time.
What are the units of current?
The units of current are Amperes (A) where 1 A is the flow of 1 C per second
What are the two components that determine the amplitude of the current?
They are the potential difference between the electrodes and the electrical conductance of the medium between them.
What is an electrical potential?
Electrical Potential is the amount of potential energy per unit of charge at a given location
What is a potential difference
Potential difference is the difference in potential between 2 locations (technically it is defined as the work needed to move a test charge from one point to another).
What are the units of potential difference?
The units of potential difference are volts (V).
What is conductance?
Conductance is the ease of flow of current between two points.
What are the units of conductance
The units of conductance are siemens (S).
What is resistance? What are the units of resistance?
Resistance is the inverse of conductance and is measured in ohms (Ω).
What is Ohm's Law
Ohm's law-- V = IR or I = gV where V is voltage, I is current, R is resistance, and g is conductance
What is a capacitor
A capacitor is 2 conductors (the solution inside and outside the cell) separated by an insulator (the membrane).
What is capacitance
Capacitance is a measure of how much charge (Q) needs to be transferred from 1 conductor to another to set up a given potential difference.
What are the units of capacitance
The units of capacitance are farads (F, and is = Q/V) where a 1F capacitor will be charged to 1V when +1C of charge is on one conductor and -1C of charge is on the other
What is the capacitance of a cell membrane
Cell membranes have a capacitance of approximately 1 µF/cm2 so the capacitance of a cell increases with membrane surface area.
What are the ions involved in neuronal excitability?
Sodium (Na+), Potassium (K+), Chloride (Cl-), Calcium (Ca2+), Magnesium (Mg2+), and Bicarbonate (HCO3-).
What is an ion transporter? What is an ion channel
Ion transporters actively move ions against concentration gradient and they also create ion gradients. Ion channels allow ions to diffuse down concentration gradient and cause selective permeability to certain ions.
What are the Extracellular/Intracellular concentrations in mM of ions in mammalian neurons?
Na+ (145/18), K+ (3/135), Ca2+ (1.2/.0001), Cl- (120/7-50).
What are the two factors that lead to the resting membrane potential
One factor is the separation of ions across the cell membrane- this creates ion gradients and the other factor is the permeability of the membrane to those ions. Ions don't go through the membrane itself as it is a lipid environment so they use specific channels.
What causes ionic separation?
This ionic separation is due to the presence of various pumps such as the Na+/K+ ATPase.
What ion is the cell membrane more permeable to?
At rest, the cell membrane is substantially more permeable to K+ than to Na+ due to more K+ channels being open. As a result, the resting membrane potential is near the K+ equilibrium potential. What is an equilibrium potential? It is the potential at which the net flux of ions into and out of the cell are equal. At the equilibrium potential for a given ion the current for that ion is 0
What is a reversal potential of an ion?
Reversal potential is when there is no net flow of ions. This doesn't mean that there isn't any ions moving; it just means the number of ions going in equals the number of ions going out.
What is the approximate reversal potential of K+? of Na+?
The approximate reversal potential of K+ is -100 mV. Na+'s reversal potential is approximately +50 mV.
What is the Nernst Equation
V = the equilibrium potential, C = the concentration of ion, R = the gas constant (2 cal mol-1 K-1), T = temperature (K), F = Faraday's constant (2.3 X 104 cal V-1 mol-1)
z = the charge of the ion
At 37o C for a monovalent cation the equation reduces to
What is the direction of flux for a positively charged ion if the membrane potential is more positive than the equilibrium potential
The direction of flux is out of the cell.
EX: If the positively charged ion is K+, and the membrane potential is +50 mV, the direction of flux would be out of the cell because K+ wants to go to its equilibrium potential of -100 mV. This makes sense because you're taking away a positive charge (positive charge is going out of the cell) which would decrease the membrane potential.
What is the direction of flux for a positively charged ion if the membrane potential is more negative than the equilibrium potential?
The direction of flux is into the cell.
EX: If the positively charged ion is Na+, and the membrane potential is -70 m, the direction of flux is into the cell because Na+ wants to go to its equilibrium potential of +50 mV. This makes sense because you're adding a positive charge (positive charge is coming into the cell), which would increase the membrane potential.
What is the modification to Ohm's Law for concentration gradient?
V- Veq=IR. This modification is used because if you use V=IR, it won't make sense at an equilibrium potential. For example, if you were at K+'s equilibrium potential of -100 mV and plugged it into the equation V=IR, you would get -100=(0)R which doesn't make sense because you can't have a voltage if the net current(I) is 0. So the modification fixes this problem. So if you're at the K+ equilibrium potential -100 mV and plug it into V- Veq=IR, you would get -100 - (-100)=IR which equals 0=IR. This makes sense because since there is no net current at an equilibrium potential, the Voltage should be zero.
If you change the concentration of an ion on either side of the membrane will it affect the equilibrium potential or the slope?
Changing the concentration of an ion on either side of the membrane will change equilibrium potential but not slope.
The resting membrane potential depends primarily on what ion concentration gradient?
The resting membrane potential primarily depends on the K+ ion concentration gradient because the cell membrane is most permeable to K+ due to a greater amount of leaky potassium channels (K+ can flow passively through these channels).
What is the Goldman-Hodgkin-Katz Equation
The Goldman-Hodgkin-Katz Equation is:
Vm=(RT/F) ln ((PNa[Na+]o + PK[K+]o)/(PNa[Na+]i + PK[K+]i))
P stands for permeability. So resting membrane potential is dominated by the K+ equilibrium potential
Is the resting membrane potential an active or passive process?
It is an active process because cells maintain the gradients using Na+/K+ ATPase, which requires energy to function
Is the resting membrane potential an equilibrium potential?
The resting membrane potential is not an equilibrium potential, as it relies on the constant expenditure of energy (e.g. ATP) by ion pumps for its maintenance. Remember that an equilibrium potential is just when the net ion flow for one ion is zero (it doesn't mean that there are no ions moving just that the total amount of ions going in equals the total amount of ions going out).
How do cells vary the permeability of the membrane?
Cells vary permeability of membrane by opening/closing channels (changes in conductance
An action potential is the result of an increasing a cell's permeability to Na+ and K+?
An action potential is the result of increasing a cell's permeability to Na+ and K+
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