CBNS 120 FULL Problem set

The slow AHP (after-hyperpolarization lasting for tens of milleseconds to seconds) results from:

Calcium Activated gK

In the Hodgkin-Huxley squid axon experiments, the late outward current could be isolated by:

B & C Only (treating the axon with TTX (tetrodotoxin) & Stepping the membrane potential to the Na equilibrium potential)

At threshold for the action potential:

The outward leak K current equals the inward Na Current

Hodgkin and Huxley theorized movement of 4 "n" gating particles from position "1-n" to "n" to describe:

K current activation

In Hodgkin-Huxley's mathematical tour de force, the "h" particle corresponds to:

The Na Channel inactivation particle

Steady state inactivation can be decreased by:

Hyperpolarizing conditioning voltage steps

Na current during the rising phase of the action potential decreases due to:

decreased driving force

Given high values of gNa and gK, at membrane potentials positive to ENa:

B & C (Na moved outward and K moved outward)

Spike frequency adaptation can be reduced by:

all of the above:

-Reducing [Ca2+]0

-Persistent gNa+

-Exposure to Cd2+

Gating current correponds to:

Movement of voltage sensors

The "Absolute Refractory Period" results from:

a & b only

-elevated threshold

Na Channel inactivation

The "Relative Refractory Period" results from:

b & c only

-elevated threshold

-k channel activation

Increasing the length of the "chain" in Shaker K channels:

slows inactivation

The structural basis for Na channel inactivation involves:

b & c

-the IFM sequence motif

-the cytoplasmic loop that connects Domain III to Domain IV

Drugs or toxins that slow or block Na channel inactivation would:

b &C

-prolong the duration of the action potential

-diminish the refractory period

Myocardial cells have comparatively long duration action potentials because of:

activation of gCa

Currents in the Hodgkin-Huxley equations include:

all of the above

-I k

-I Na

-I C

During the relative refractory period:

b & c

-action potential initiation can be accomplished by imposing a stronger stimulus

-threshold is elevated

Persistent Na current (INaP):

all of the above

- can cause repetitive action potential

-produces an after depolarization

- can oppose the influence of I K Ca

During the absolute refractory period:

all of the above

-gK is high

-Sodium channels are inactivated

-threshold is essentially infinite

As the number of myelin wraps around an axon increases:

a & c

-r in increases

-r i decreases

-Cin decreases

Which of the following would increase conduction velocity in an unmyelinated axon

A & B only

-increasing axon radius

-decreasing T

Purkinje neurons:

all of the above

-have voltage gated Ca2+ channels in their dendrites

-have somatic Na+ action potentials

-have dendritic action potentials

Gap junctions:

all of the above

operate at electrical synapses

provide for electrical synchrony between cells

provide for biochemical synchrony between cells

Gap junctions are composed of:

-Connexins

-Hemichannels

-12 subunits

Consider a myelinated axon having Em of -80 mV. Threshold to elicit an action potential is -40 mV. An action potential (100 mV amplitude, measured from Em to peak) arrives at the first node of Ranvier. Local current flowing ahead of the spike reaches the second node, the distance being x = 0.25λ. Calculate the magnitude of the depolarization caused by local current reaching the second node using the equation: Vx = Voe-x/λ.

78 mV

Consider a myelinated axon in a patient with a neurodegenerative disease, whereby partial demyelination has occurred. Under this condition, less myelin means more capacitance in the internode, allowing more current to flow across the membrane, decreasing the length constant. In fact, under this scenario, the length constant over distance x from the first node to the second node is x = λ. Calculate the depolarization caused by the local current in advance of the 100 mV spike in this new scenario, assuming Em of -80 mV and threshold is -40 mV as before.

37 mV

Consider the previous question. Does the depolarization at the second node reach threshold? In other words, does the spike continue to propagate past the second node or does it fail?

no

The length constant (λ)

increases as ri decreases

In the Node of Ranvier:

Na channels are more abundant than in the internode & rin is lower than in the internode

The time constant (τ)

increases with increasing cin

increases with increasing rin

The Nernst Equation is used to predict:

The equilibrium potential of a single membrane permeant ion

The Goldman Equation is used to predict:

>The equilibrium potential of a single membrane-permeant ion

>The contribution of multiple permeant ions to Em

Consider the frog muscle study published by Hodgkin and Horowicz (1959) that was presented in Lecture 5. Doubling [K]o from 10 mM to 20 mM would have the following effect on Em:

depolarization

Given what you now know about the squid giant axon and the NCX (Na/Ca Exchanger), what effect(s) would you predict as a consequence of decreasing [Na]o? (check all possible answers)

>Depolarize the cell

>Reduce the amplitude of action potential

>Increase intracellular Ca Concentration

The Steady State Equation is used:

All of the Above ( to predict Em, to predict the contribution of Na/K ATPase to Em, to predict the contribution of multiple membrane-permeant ions to Em)

Predict the resting potential (Em) for a neuron, where [K]i = 95 mM, [K]o = 5 mM, [Na]in= 15 mM, [Na]o= 140 mM, at room temperature (T=298oK), with R=8.3 coul-volts/deg-mol, F = 96,500 coul/mol. Assume that the Na permeability of the cell membrane is 1/50 that of the K permeability, that the neuron is bathed in ouabain, and that chloride ions are in equilibrium and hence do not contribute to Em.

-64 mv

Refer to the previous scenario (Question 6). Predict the value of Em following removal of ouabain from the bathing medium.

-67 mv

In frog muscle cells, reducing [Cl]o from 120 mM to 30 mM would have the following effect on Em:

Depolarization followed by a return to the original value of Em

During the rising phase of the action potential, the following occur (pick the best answer):

gNa increases

During the falling phase of the action potential, the following occur (pick the best answer):

B & C only (gK increases & Na channels inactivate)

The negative after-potential that follows the falling phase of the action potential occurs because:

Total gK exceeds to leak gK

In the squid axon, where EK is more negative than Em because of low, but significant gNa, an increase in leak gK would (choose all that apply):

hyperpolarize the membrane, cause decreased excitation

Consider the early inward current and late outward current recorded by voltage clamp from the squid axon. The late outward current could be isolated by the following procedures (choose all that are correct):

exposure to tetrodotoxin, stepping the membrane voltage to ENa

Consider the early inward current and late outward current recorded by voltage clamp from the squid axon. The early inward current could be isolated by the following procedures (choose all that are correct):

treatment with TEA (tetraethylammonium)

Hodgkin and Huxley theorized that, in response to depolarization, movement of 4 "n" particles in the membrane from a position or state of "1-n" to "n" led to::

activation of I K

Hodgkin and Huxley theorized that, in response to depolarization, movement of 3 "m" particles in the membrane from a position or state of "m-1" to "m" led to:

Activation of I Na

In the Hodgkin and Huxley description of current flow during the action potential, a single "h" particle moving from a state "h" to "1-h" accounted for:

Inactivation of I Na

ATPases (pumps) like the Na/K Pump transfer ions across the membrane at rates of

10^0-10^3

In voltage-gated channels, the S4 transmembrane segment functions as a and the loop between S5 and S6 functions as the .

Voltage Sensor; Pore

Ligands that activate channels from the cytoplasmic side of the membrane include

Cyclic GMP; Calcium

Regions of channel proteins that cross the membrane from one side (e.g., extracellular) to the other (e.g., cytoplasmic) are called:

A & B only (Membrane Spanning & Transmembrane Segments)

Neuronal nicotinic receptors can be formed from:

A & C only (alpha and beta segments & alpha only)

Nicotinic receptor subunits have which number of transmembrane segments?

4

The following are specific blockers of the Na/K Pump: (Choose all that are correct)

ouabain & digoxin

The transporter that sequesters Ca in the endoplasmic reticulum is:

The SERCA pump

The alpha subunit of voltage-gated Na channels has how many transmembrane segments?

24

Injection of Na ions into a neuron would: (check all possible answers)

Hyperpolarize the membrane potential & Activate the Na/K pump

A complete cycle of the Na/K ATPase requires:

all of the above (Na binding, K binding, Phosphorylation, Dephosphorlation)

Match the questions and answers

1. Na/K ATPase

2. Na/Ca Exchanger (NCX)

3. SERCA pump

4. NaKCC1

1. Electrogenic

2. Driven by NA Gradient

3. Ca ATPase

4. Sympoter

Secondary transporters derive their energy from:

B- Ion Gradients

During a cycle of the Na/Ca (NCX) exchanger:

A & C (NA enters the cell and Ca is extruded & An inwardcurrent flows)

Secondary transporters move ions across the membrane at rates of:

10^2-10^4

Decreasing [Na]o would affect the Na/Ca (NCX) exchanger as follows:

Decrease transporter activity

Blocking the Na/K pump could:

All of the Above

The following amino acids are positively charged:

A &C (Lysine and Arginine) (X)

Cajal used the [_________] stain to prove the [___________] Doctrine.

Golgi; Neuron

Conductance is the reciprocal of:

Resistance

Hyperpolarization occurs when the membrane potential becomes more [_____________], while depolarization causes the membrane potential to become more [_______________].

Negative; Positive

Permeability is the ability of the membrane to conduct _________ .

Ions

Permeability indicates the presence of [A], while conductance requires [B] and [C].

Open Channels; Ions, Permeability

Categories of ion channels include [A], [B], and [C].

Voltage Activated, Ligand Activated, Stretch Activated

Conductance can be distinguished from permeability by the requirement for [A].

Charge

The membrane potential at which the diffusional force created by an ion gradient is equal and opposite to the electrical force is called the [________________].

Equilibrium Potential

The difference between the membrane potential (Vm) and the equilibrium potential (Ex) for any given ion is called [_____________].

Driving Force

When the magnitude of current flow across the membrane in one direction exceeds current flow in the opposite direction, it is called ___________.

Rectification

Ion channels flux (transfer) ions across the membrane at rates of

10x8^7

In the figure depicted below, current is plotted as a function of voltage. Two linear I-V relationships are shown. The lines are parallel. The slope of line A is defined as

In the previous question, the conductance of A is __________ the conductance of B.

Equal to

In Question 12, the equilibrium potential of I-V relationship A is [A] and the equilibrium potential for B is [B].

-75, -50

In the figure depicted below, the conductance of A is [A], [B], [C] the conductance of B.

Greater than

Driving Force is:

all of the above

Ion channel activity is:

all of the above

The graph below displays:

Outward flow

Sympathetic input to the heart releases _______, which activates the ________, resulting in dissociation of _______ and increased activity of _______.

A,B,C,D - (norepinephrine, beta-adrenergic receptor, Gs, adenylyl cyclase)

The _____ nicotinic receptor increases _______ conductance directly, whereas the ________ muscarinic receptor increases ________ conductance indirectly.

A,B,C,D- (ionotropic, sodium, metabotropic, GIRK channel)

G protein inhibition of N-type Ca channels in sympathetic neurons occurs through direct binding of ______ to the channel:

C- the By(beta gamma) subunit

The following are endocannabinoids:

E- A & C only (anandamide & 2-AG)

Cardio acceleration by norepinephrine involves synthesis of _______, which binds to the _______. leading to a shift in its _______ to more _________ potentials.

A,B,C,D- (cAMP, HCN channel, voltage-dependent activation, positive)

Activation of Gs leads to elevated levels of _____, while activation of Gi shifts voltage-dependent activation of the _____ in the negative direction. Gq activation causes activation of ______, while activation of Go places voltage-dependent calcium channels in a ______.

A,B,C,D- (cAMP, HCN channel, phospholipase C(PLC), reluctant state)

The minutes-long slow EPSP observed in sympathetic ganglion neurons results from

D- all of the above (reduced probability of M-channel opening, reduced membrane conductance, dissociation of PIP2 from the M-channel)

Which of the following shift the voltage-dependent activation curve of HCN in cardiac pacemaker cells from blue to green?

C- acetylcholine

Acetylcholine action on endothelial cells activates the _____ leading synthesis of _________ and activation of ______ in the adjacent smooth muscle cell, leading to ___________.

A,B,C,D- (mAChR, No, guanylyl cyclase, vasodilation)

Which of the following shift the voltage-dependent activation curve of HCN from blue to orange?

A- cAMP

Vagal nerve mediated parasympathetic input to the heart causes:

E- B & C only (slowing of heartbeat, reduction of cAMP)

Which of the following contribute to elevation of cytoplasmic calcium levels?

E- A & B only (Gs & Gq)

The following put calcium channels into a "reluctant" state:

D- all of the above (alpha 2 adrenergic receptor, CB1R, By subunit)

Which of the following shift the voltage-dependent activation curve of HCN from blue to orange?

A- norepinephrine

GPCR activation leads to a multi-step signaling cascade. Which of following are amplification steps?

E- A & C only (receptor induced G-protein activation & cyclic AMP synthesis by adenylyl cyclase)

The following promote(s) gaseous transmission in vascular tissue:

D- all of the above (NOS (nitric oxide synthase), sildenafil (Viagra), PKG)