Lecture 3 - Electrical Signals of Nerve Cells (The Resting Membrane Potential) Flashcards
What is the name of this equation?
Nernst Equation
True or False?:
Capacitance is a measure of permeability to ionic flux.
False
Conductance is a measure of permeability to ionic flux.
True or False?:
Ion channels are protein structures.
True
True or False?:
Under normal conditions, the Vm is set solely by ENa.
False
Under normal conditions, the Vm is set by some balance of the EK, ENa, and ECl.
Why can’t ions cross the membrane without channel proteins? What do ion channels do to selectively allow them to cross the membrane?
Ions in solution carry a hydration shell which can not pass through the hydrophobic interior of the lipid bilayer membrane. Ion channels selectively strip ions of this hydration shell so that they can cross.
True or False?:
Just like at rest, changing [Na]O during an action potential has a very little impact on membrane voltage.
False
Unlike at rest, changing [Na]O during an action potential has a large impact on membrane voltage.
True or False?:
Receptor & synaptic potentials are graded. Action potentials are “all-or-nothing” and generative.
True
True or False?:
One way to think about the resting membrane potential is that its a way for the cell to store energy in the form of ion gradients.
True
Explain why there is flux of K+ from 1 to 2 on the left, no flux of K+ in the middle, and flux of K+ from 2 to 1 on the right (membrane is permeable to K+).
On the left, there is no electromotive force to move ions so the only factor is the concentration gradient, which moves K+ from where there is a high concentration (compartment 1) to a low concentration (compartment 2). In the middle, the voltage is set at the equilibrium voltage (given by the Nernst equation), so the movement from compartment 1 to compartment 2 due to the concentration gradient is equal to the movement from compartment 2 to compartment 1 due to the charge imbalance. On the right, the charge imbalance is increased, so there is more movement from compartment 2 to compartment 1 due to that than from compartment 1 to compartment 2 due to the concentration gradient.
What does the Nernst equation do?
The Nernst equation restates the concentration gradient in electrical terms (membrane voltage at which there is no net movement of ions). It finds the most energetically favoured membrane voltage for a given concentration gradient across the membrane.
If you inject negative current into a cell, does it depolarize or hyperpolarize the cell?
Hyperpolarize
Explain what is happening in the following diagram.
A membrane permeable only to K+ (gold spheres) separates compartments 1 and 2, which contain the indicated concentrations of KCl. As K+ ions diffuse and encounter the membrane channels, more will pass from the side where [K+] is higher, simply by chance. Consequently, there is a net movement of K+ ions from the high concentration (compartment 1) to the low concentration (compartment 2) sides. However, this now separates the positive charge of the K+ ions (compartment 2) from the negative charge of the Cl- ions (compartment 1), creating an electrical potential difference between the two sides. This potential difference results in an electrostatic force that drives K+ ions back from compartment 2 to the negative compartment 1 (because opposites attract). At equilibrium, the number of K+ ions diffusing down their concentration gradient into compartment 2 equals the number of K+ ions drawn back into compartment 1 due to the charge inbalance.
Who discovered the squid giant axon’s function?
John Z. Young
The GHK equation calculates a weighted “average” of Nernst potentials for multiple ions, using relative permeabilities as the weighing factor.
True
What ions contribute to the resting membrane potential? Do they all contribute equally?
Sodium, potassium, and chloride contribute to the resting membrane potential. Though, they don’t all contribute equally.
How does the negative resting potential help the neuron?
The normal negative resting membrane potential helps the neuron because it is a way to store the energy used for rapid signaling.
True or False?:
Applying a voltage across the membran will modify its ionic flux.
True
What is the diameter of the squid giant axon? What is the diameter of a mammalian axon?
The squid giant axon has a diameter of approximately 800 µm while a typically mammalian axon is approximately 2 µm in diameter.
Do ion transporters or ion channels create ion concentration gradients?
Ion Transporters
What is the advantage to having a hyperpolarized resting membrane potential?
Cells have a hyperpolarized resting membrane potential so that they can send signals very rapidly without having to consume ATP or do some sort of slow metabolic reaction. They use ATP earlier through the transporters to establish a gradient that gives them access to “instant energy” to move charge across the membrane and propagate signals.
How does varying the membrane permeabilities for Na+ and K+ cause an action potential?
At rest, the membrane is more permeable to potassium than sodium. Since potassium’s equilibrium potential is very low (-84 mV), it results in a negative, hyperpolarized membrane potential. During an action potential, the membrane permeability of sodium increases and becomes greater than that of potassium. Since sodium’s equilibrium potential is very high (+57 mV), it has a very large driving force that causes sodium to rush into the cell to depolarize it to a positive potential closer to that of sodium’s equilibrium potential. After the peak of the action potential, the permeability of sodium decreases back to its resting permeability and the cell goes back to its resting potential.
True or False?:
Chemical diffusion is balanced by electrostatic forces at equilibrium.
True
Glutamate receptors pass both K and Na upon binding glu. Why does this cause depolarization?
This causes the membrane to depolarize towards the average of EK and ENa which is close to 0 mV. This is the basis of the so-called excitatory postsynaptic potential (EPSP).
True or False?:
The GHK equation describes in electrical terms (mV) the force produced by each ion’s gradient. The Nernst equation predicts the resting membrane potential (Vm) at which all 3 ions will be at equilibrium.
False
The Nernst equation describes in electrical terms (mV) the force produced by each ion’s gradient. The GHK equation predicts the resting membrane potential (Vm) at which all 3 ions will be at equilibrium.