Deck 8: Electrical Signaling in Neurons

Question 1

How does the size of a cell influence its input capacitance and resistance?

A) The larger the cell is, the larger its input capacitance and resistance will be.
B) The larger the cell is, the smaller its input capacitance and resistance will be.
C) The input capacitance increases with cell size, whereas the input resistance decreases with cell size.
D) The input capacitance is inversely proportional to cell size, whereas the input resistance is directly proportional to it.
E) The size of the cell does not influence either the input resistance of capacitance, because both values are exclusively determined by the molecular composition of the cell membrane.

Answer 1

C

Question 2

Is the specific membrane resistance (R_m) expressed in  cm²?

A) Yes, because it varies depending on the phospholipid composition of the membrane bilayer.
B) Yes, because it depends on the number of open channels in a given surface area.
C) No, the specific membrane resistance is measured in .
D) No, the specific membrane resistance is measured in /cm².
E) No, because the specific membrane resistance does not vary with cell size.

Answer 2

B

Question 3

Which formula allows you to calculate the membrane time constant _m?

A) _m = R_m/4r²
B) _m = ir_input
C) _m = C_m V
D) _m = R_m C_m
E) _m = ΔV_max e^(-t/τ)

Answer 3

D

Question 4

What is the membrane conductance of a cell with a specific membrane resistance of 1,000  cm² and 50,000  cm²?

A) The first cell has a specific membrane conductance of 1  10⁹ pS/cm², the second cell has a specific membrane conductance of 2  10⁹ pS/cm². Therefore, the first cell has a larger surface density of open channels.
B) The first cell has a specific membrane conductance of 1  10⁹ pS/cm², the second cell has a specific membrane conductance of 2  10⁷ pS/cm². Therefore, the first cell has a smaller surface density of open channels.
C) The first cell has a specific membrane conductance of 100  10⁷ pS/cm², the second cell has a specific membrane conductance of 2  10⁷ pS/cm². Therefore, the first cell has a larger surface density of open channels.
D) The first cell has a specific membrane conductance of 1  10⁷ pS/cm², the second cell has a specific membrane conductance of 0.5  10⁷ pS/cm². Therefore, the first cell has a smaller surface density of open channels.
E) The first cell has a specific membrane conductance of 1  10⁹ pS/cm², the second cell has a specific membrane conductance of 2  10⁷ pS/cm². These values do not depend on the surface density of open channels.

Question 5

In cortical neurons, you can identify the following five sub-cellular compartments. If you were to apply a sub-threshold current step of fixed amplitude to each one of them, where would you evoke the smallest change in membrane potential?

A) Soma
B) Terminal dendrites
C) Proximal dendrites
D) Axon
E) Axon initial segment

Question 6

Why is the effect of injecting a pulse of correct in a dendrite more complex than the one evoked by injecting a pulse of current in a spherical cell?

A) Because the molecular composition of the dendritic membrane is different from that of a spherical cell, due to the presence of specific types of ion channels.
B) Because it is not possible to study the biophysical properties of small, sub-cellular compartments like dendrites.
C) Because the current injected in a dendrite only flows outward through the cell membrane.
D) Because the cross section of dendrites varies along the length of the dendrite.
E) Because the dendritic compartment cannot be represented by only one RC circuit as the injected current flows along the length of the dendrite and not just across the membrane.

Question 7

What relationship describes how the amplitude of a membrane potential change varies with the distance from a current injection site?

A) ΔV = ΔV₀ e^-t/τ
B) ΔV = ΔV₀ e^-x/λ
C) ΔV = ΔV₀ (1 - e^-t/τ)
D) ΔV = ir_input
E) ΔV = Q/C

Question 8

How does the membrane resistance affect the membrane length constant?

A) The membrane length constant increases as the membrane resistance increases.
B) The membrane length constant increases as the membrane resistance decreases.
C) The membrane length constant does not depend on the membrane resistance.
D) The membrane length constant only changes if the resistance of the cytoplasm changes.
E) The membrane length constant cannot be calculated when the membrane resistance changes.

Question 9

What is the membrane length constant of a cell with membrane resistance r_m = 1  cm and cytoplasmic resistance r_i = 100 /cm?

A) λ = 0.1 mm
B) λ = 1 mm
C) λ = 10 mm
D) λ = 1 cm
E) λ = 10 cm

Question 10

Does the effect of an inhibitory input change depending on whether it targets a dendritic compartment with a small or large cross section?

A) Yes, the change in membrane potential caused by the inhibitory input will be larger in dendrites with larger cross-section because the membrane resistance is directly proportional to dendrite diameter.
B) No, the change in membrane potential caused by the inhibitory input will be the same in dendrites with large and small cross-sections, because it is not influenced by the cross section of these processes.
C) Yes, the change in membrane potential caused by the inhibitory input will be larger in dendrites with smaller cross-section because the membrane resistance is inversely proportional to dendrite diameter.
D) No, the change in membrane potential caused by the inhibitory input will be the same in dendrites with large and small cross-sections, because the membrane and cytoplasmic resistance of these compartments is the same.
E) The effect of the inhibitory input depends only on the local density of voltage-gated sodium and potassium channels.

Question 11

What is the relation between the membrane capacitance (c_m) and the specific membrane capacitance (C_m)?

A) c_m = C_m
B) c_m = C_m(πa²)
C) c_m is calculated at 20C, whereas C_m is calculated at 37C.
D) c_m is independent on fiber size, whereas C_m varies inversely proportionately to it.
E) c_m = C_m(2πa)

Question 12

In mammals, the specific membrane resistance is

A) smaller than in squids, where the intracellular ion concentration is lower.
B) smaller than in frogs, where the intracellular ion concentration is lower.
C) similar to that of other non-mammalian species including squids and frogs.
D) comparable to that of copper.
E) much smaller than copper, making the conduction of electrical signals particularly efficient.

Question 13

What is an electrotonic potential?

A) It is a change in membrane potential analogous to that evoked by an action potential.
B) It is a graded potential that relies on the opening of voltage-gated ion channels.
C) It is the potential change at the point of current injection.
D) It is a graded potential that becomes progressively smaller as it spreads along the cell membrane.
E) It is a spontaneous fluctuation in the resting membrane potential of a cell.

Question 14

What is the distance occupied by an action potential, if you could freeze it in time, assuming it lasts 1 ms and travels at a speed of 10 m/s?

A) 10 mm
B) 20 mm
C) 1 mm
D) 2 mm
E) 0.5 mm

Question 15

What is the main difference between the α, β, and δ sub-types of vertebrate group A myelinated fibers?

A) Size
B) Extent of myelination
C) Action potential conduction velocity
D) Identify of their cellular target
E) Protein composition

Question 16

What is the main contributor to the refractory period following the onset of an action potential?

A) Inactivation of voltage-gated sodium channels
B) Closing of voltage-gated sodium channels
C) Opening of leak potassium channels
D) Sodium influx
E) Potassium efflux

Question 17

Which cells form myelin sheets in the central nervous system?

A) Schwann cells
B) Astrocytes
C) Microglia
D) Neurons
E) Oligodendrocytes

Question 18

How many lamellae of myelin typically wrap large nerve fibers in the vertebrate nervous system?

A) 10-20
B) 20-40
C) 140-160
D) 10-160
E) None

Question 19

What is the name of the periodic interruptions of myelin sheets along nerve fibers?

A) Schwann cells
B) Nodes of Ranvier
C) Synapses
D) Hot spots
E) Nerve knots

Question 20

What is the main function of M-channels at the node of Ranvier?

A) They prevent ectopic action potential discharges.
B) They promote action potential propagation.
C) They depolarize the membrane potential.
D) They prolong the refractory period.
E) They promote myelination.

Question 21

How can you test the hypothesis that demyelination disrupts the confined expression of voltage-gated sodium channels in the node of Ranvier?

A) By analyzing the effect of diphtheria toxin on action potential repolarization
B) By changing the ionic composition of the extracellular solution where the isolated nerve fiber is stored
C) By severing nerve fibers
D) By using pharmacological agents that block KCNQ2-containing M-channels
E) By comparing the sodium channel distribution along myelinated and demyelinated fibers treated with diphtheria toxin

Question 22

What is the functional advantage of having few shorter internodes before an unmyelinated nerve terminal?

A) It ensures that action potentials do not invade nerve terminals.
B) It increases the number of branch points and therefore promotes conduction block.
C) It serves to boost local depolarization of nerve terminals and promote neurotransmitter release.
D) It prevents neurons from reaching the threshold for action potentials, preventing hyperactivity.
E) It simplifies the geometry of the nerve ending.

Question 23

Which ion channels are highly concentrated in the nodes of Ranvier?

A) Delayed rectifier potassium channels
B) Sodium channels
C) Calcium channels
D) Leak channels
E) None of the above

Question 24

How does the passive spread of current ahead of the active region of a nerve fiber contribute to action potential propagation?

A) It provides directionality to the propagation of the action potential.
B) It changes the speed at which the action potential propagates.
C) It causes a new segment of the cell membrane to be depolarized to threshold.
D) It allows the action potential to propagate only along a portion of the nerve fiber.
E) It promotes action potential attenuation.

Question 25

Which ion channels are abundant in the paranodal region?

A) Voltage gated sodium channels
B) Slowly inactivating potassium channels
C) M-channels
D) Delayed rectifier potassium channels
E) Leak channels

Question 26

Which pathological states are known to be associated with genetic mutations that impair the function of the potassium channel subunit KCNQ2?

A) Heart arrhythmia
B) Epileptic seizures and myokymia
C) Coma
D) Cerebellar ataxia
E) Parkinson's disease

Question 27

How do branch points affect action potential propagation?

A) They increase the membrane area that is depolarized by the action potential.
B) They increase the local membrane resistance.
C) They promote action potential propagation through higher order branches.
D) They delay action potential propagation.
E) They increase the local values of membrane resistance and capacitance.

Question 28

In 1955, J.C. Eccles and colleagues made which fundamental experimental observation regarding cell excitability and action potential generation?

A) Dendritic depolarization initiates action potentials near the soma, not in the dendrites.
B) Dendrites are generally unexcitable and only transmit signals passively towards the soma.
C) Action potentials travel along dendrites with a conduction velocity of 3 m/s.
D) Cerebellar Purkinje neurons produce dendritic action potentials.
E) Action potentials are initiated in the axon initial segment, and then propagate along the axon and back into the soma and dendrites.

Question 29

Modest activation of distal synapses produces a local dendritic depolarization that propagates electrotonically towards the soma and can trigger an action potential at the soma. Stronger activation of distal synapses evokes a dendritic calcium action potential that also results in the generation of a somatic action potential. How can you distinguish these two scenarios using dual somatic and dendritic recordings?

A) With modest stimuli, the action potential recorded from the soma precedes the one recorded from the dendrite. With stronger stimuli, the action potential recorded from the soma follows the one recorded from the dendrite. In addition, in this case, the two action potentials display a shorter latency.
B) With modest stimuli, the action potential recorded from the soma is smaller than the one recorded from the dendrite. With stronger stimuli, the action potential recorded from the soma is larger than the one recorded from the dendrite.
C) With modest stimuli, the action potential recorded from the soma is longer than the one recorded from the dendrite. With stronger stimuli, the action potential recorded from the soma is shorter than the one recorded from the dendrite.
D) With modest stimuli, there is typically no action potential recorded from the soma. With stronger stimuli, the action potential recorded from the dendrite shows an after-depolarization, which cannot be detected from the soma.
E) The two recordings are indistinguishable using these experimental configurations.

Question 30

Which factors make propagation of electrical signals in dendrites more complex than in axons?

A) The membrane capacitance of dendrites differs from that of neurons.
B) Dendrites do not express voltage-gated ion channels.
C) Dendrites contain a wide variety of voltage-gated ion channels and different branches have different input resistance, which varies with the activity of excitatory and inhibitory synapses.
D) Dendrites do not receive excitatory and inhibitory synaptic inputs.
E) Dendrites typically have smaller input resistance than axons, which prevents efficient propagation of electrical signals.

Question 31

What type of active signals can you record by delivering supra-threshold current injections to dendrites located away from the soma of cerebella Purkinje neurons?

A) Fast sodium action potentials
B) Fast hyperpolarizing potentials
C) Action potentials propagating passively from the soma
D) Long-duration calcium action potentials
E) None, because no action potential makes it to dendrites away from the axon initial segment

Question 32

Which of the following cells does not exhibit electrical coupling?

A) Cardiac cells
B) Smooth muscle cells
C) Epithelial cells
D) Gland cells
E) Purkinje cells

Question 33

What structures ensure electrical coupling among cells?

A) Synapses
B) Gap junctions
C) Dendrites
D) Axons
E) Neurons

Question 34

What is a connexon?

A) It is the name of each of the six proteins forming the pore of a gap junction.
B) It is the portion of the extracellular space through which currents flow.
C) It is an intracellular structure coupling adjacent organelles.
D) It is an assembly of six proteins forming the pore of a gap junction.
E) It is the name of the non-pore-forming portion of an electrical junction.

Question 35

How many subunits (connexins) does a connexon have?

A) 6
B) 5
C) 4
D) 3
E) 2

Question 36

What is the typical diameter of a connexon?

A) 100 nm
B) 1 nm
C) 10 nm
D) 1 m
E) 10 m

Question 37

A connexon assembled from more than one type of connexins is called

A) homomeric.
B) heteromeric.
C) heterotypic.
D) homotipice.
E) heteroconnexon.

Question 38

Which type of connexons have high permeability to ATP and glutamate?

A) Cx32
B) Cx36
C) Cx40
D) Cx26
E) Cx43

Question 39

What is the size of the largest molecular than can pass through the pore of gap junctions?

A) 1 KDa
B) 100 Da
C) 10 Da
D) 1 Da
E) Gap junctions are only permeable to ions

Question 40

How do even the lowest single-channel conductance gap junctions provide a significant path for current flow between cells?

A) Their single-channel conductance can be modified by neuronal activity.
B) There is a large driving force that favors ion movement across gap junctions.
C) They are typically expressed at a local high density.
D) Ions lose their hydration shell as they pass through the pore of gap junctions.
E) Even the lowest single-channel conductance gap junction forms a very wide pore for the movement of ions across the membrane.

Question 41

Which features does not allow you to identify gap junctions between two neuronal processes in electron microscopy images?

A) There is no synaptic vesicle on either side of the junction.
B) The space between the two membranes is narrower than outside of the gap junction.
C) There is an electron-dense thick region on both sides of the membrane.
D) The connexins of each connexon are readily visible with electron microscopy resolution.
E) The gap junction can be formed between two dendrites.

Question 42

How many transmembrane helices does each connexin have?

A) 3
B) 4
C) 6
D) 7
E) None

Question 43

What are the input resistance and capacitance?

Question 44

What are the specific membrane resistance and capacitance?

Question 45

What is the equivalent electrical circuit of a cell?

Question 46

How do the membrane length and time constant affect the electrotonic propagation of sub-threshold changes in membrane potential?

Question 47

Why do action potentials propagate along a preferred direction?

Question 48

How does the distribution of ion channels vary along the length of myelinated fibers?

Question 49

Which experiments would you perform to test the hypothesis that there is a heterogeneous distribution of ion channels in myelinated fibers?

Question 50

Which structural features of neurons contribute to action potential conduction block?

Question 51

What experimental findings supported the notion that action potentials arise from the axon initial segment?

Question 52

How do action potentials back-propagate along dendrites?

Question 53

How do dendritic excitatory and inhibitory synaptic inputs affect back-propagating action potentials?

Question 54

What are the functional benefits of having electrical coupling among cells?

Question 55

How do different types of connexons differ from one another?

Question 56

How does the single-channel conductance and local density of connexons affect electrical coupling among cells?