Midterm1_F13_W

Question 1

Info:
Ex = -70 mV
Ey = -50 mV
Ez = +65 mV
The threshold for firing action potentials is –25 mV.

What range of membrane potentials, Vm, would be possible for the cell if its
membrane contained only X, Y, and Z selective channels?

Answer 1

-70mV to +65mV

Question 2

Info:
Ex = -70 mV
Ey = -50 mV
Ez = +65 mV
The threshold for firing action potentials is –25 mV.

Ion Z is in higher concentration outside the cell than inside. What is its
charge

Answer 2

Positive

Question 3

Info:
Ex = -70 mV
Ey = -50 mV
Ez = +65 mV
The threshold for firing action potentials is –25 mV.

If Vm = -70 mV, and Y ions are (-), what will be the direction
of Y ion flow through open Y channels?

Answer 3

Out of the cell

Question 4

Info:
Ex = -70 mV
Ey = -50 mV
Ez = +65 mV
The threshold for firing action potentials is –25 mV.

If Vm = -70 mV, what effect would opening more Z-selective channels have
on the membrane potential?

Answer 4

Depolarize the cell

Question 5

Info:
Ex = -70 mV
Ey = -50 mV
Ez = +65 mV
The threshold for firing action potentials is –25 mV.

If Vm = -70 mV, opening which channels would result in a depolarizing,
inhibitory potential?

Answer 5

Y selective channels

Question 6

During an action potential, the membrane’s Na+ channels open and Na+ ions enter the
cell.

What effect does this Na+ influx have on the concentration of Na+ inside the
neuron?

Answer 6

No effect - Only a very small fraction of the ions that are in free solution in the cell move during the AP, so
the is no measurable effect on [Na+]i

Question 7

What is an EPSP?

Answer 7

An Excitatory Postsynaptic Potential - a depolarization of the postsynaptic membrane in
response to neurotransmitter release

Question 8

What do you use to record EPSPs?

Answer 8

current clamp

Question 9

Which technique was the focus of the article you read by Sakmann and
Neher?

Answer 9

patch clamp

Question 10

Why were patch clamps a major breakthrough?

Answer 10

It allowed researchers to measure and study the properties of a single (or a few) channels

Question 11

Which technique would you use if you wanted to record currents from
individual ligand-gated receptors?

Answer 11

outside-out patch

Question 12

What component of a biological membrane gives it the property of
capacitance?

Answer 12

the lipid bilayer

Question 13

What component gives it the property of conductance?

Answer 13

channels

Question 14

For each property, explain why channels confers this property of conductance.

Answer 14

the lipid bilayer does not allow ions to cross - separates charge, acting as a capacitor

the channels allow ions to flow through the lipid bilayer, acting as a conductor

Question 15

You are studying passive spread of electrical currents in two different neuronal types
(A and B) and discover that neuronal type A has a larger length constant than neuronal type B.
What properties of these cells could underlie this difference?

Answer 15

Neuronal type A must either fewer channels open (higher membrane resistance) or larger
diameter neurites (lower internal resistance).

Question 16

How are neurotransmitters removed from the synaptic cleft? Describe 3 different mechanisms and name a neurotransmitter for each mechanism

Answer 16

Diffusion: all NTs OK here
Degradation: Acetylcholinesterase breaks actylcholine down into choline and acetate
Uptake: glutamate (and GABA though we didn’t mention it much) is taken up by surrounding glial cells
through specific glutamate transporters.
Re-uptake: serotonin is taken up by releasing neuron through specific serotonin transporters

Question 17

The intracellular
chloride concentration is 10 mM, the extracellular chloride concentration is 100 mM.
The cell is at room temperature.
What is the chloride equilibrium potential?

Answer 17

-58mV

Question 18

When the brain is deprived of oxygen, mitochondria inside neurons stop
producing ATP. What effect does this have on the resting membrane potential of
neurons?

Answer 18

The membrane potential will rapidly depolarize about 11 mV and then more slowly depolarize
up to zero mV. Without ATP, the Na/K ATPase cannot work. This will initially remove the electrogenic effect
of the pump, depolarizing the membrane potential about 11 mV. It will then over time result in a
breakdown of the sodium and potassium concentration gradients until both ions are found in
equal concentrations on the two sides of the membrane, at which time the membrane potential
will equal 0 mV.

Question 19

You are studying a neuron that is in every way a typical
neuron, except that it does not have any voltage gated potassium channels. In what
ways will this neuron’s action potential differ from a normal neuron’s action potential?
Explain the causes of the differences

Answer 19

1) The peak of the AP will be more positive, because there is no outward current through voltage
gated K channels to bring it down (it still won’t reach the Na+ equilibrium potential because K+
leak channels are open).
2) The repolarization phase of the AP will proceed more slowly, because there is no outward
current through voltage gated potassium channels to repolarize the cell quickly (note that the cell
does still repolarize as voltage gated Na channels inactivate and the K leak current brings the
membrane potential back to the resting membrane potential)
3) There will be no undershoot (after hyperpolarization) because there is no outward current
through voltage gated potassium channels to bring the membrane potential down below resting
membrane potential.
4) There will be a shorter refractory period, because there will be no outward current through
voltage gated potassium channels to make it harder for the cell to reach AP firing threshold