BBB 109 midterm 1 recitation

List 2 ways neurotransmitters in the synaptic cleft can be cleared and the mechanisms involved in each.

1) Degradation: enzymes in synaptic cleft or presynaptic terminal 2) re-uptake: transporters in presynaptic terminal or in neighboring astrocyte

Neuropharmacology offers us a powerful tool kit to directly and specifically manipulate the nervous system. Predict the effects of the following drugs on synaptic transmission. Be sure to 1) name the neurotransmitter(s) affected and 2) how the drug would affect the postsynaptic response (e.g. increase, decrease). c)Donepezil (inhibitor of acetylcholinesterase):

Acetylcholine would be specifically affected; increase PSP for same reason as previous

Which of the following ions would have the greatest driving force? K+ Na+ Cl- Ca2+

Ca2+

Indicate how each of the following would likely change the amplitude of an isolated EPSP from a glutamatergic synapse, which has both AMPA and NMDA receptors. Treat with botox, which cleaves the SNARE proteins

Decrease

Name of Phase 2. gNa or gK higher? V-gated Na+ channel state V-gated K+ channel state

Depol/synaptic input gNa Opening Closed

If a channel's conductance to Na+ is equal to its conductance to K+, would that channel hyperpolarize or depolarize our hypothetical cell? Why?

Depolarize because the DF of Na is greater than the DF of K (1pt depol, 1 pt DF)OR Erev is right in between ENa and EK, so that it would be depol (1pt depol, 1 pt Erev)

How does the mutation affect the resting membrane potential, relative to the normal resting membrane potential? (circle one) Hyperpolarizes Repolarizes Underpolarizes Depolarizes No change

Depolarizes

Given the equilibrium potentials below, if we have a neurotransmitter receptor that is selective for X+ and Y+ and conducts them both equally well, what type of PSP would we see if the membrane potential is -75mV? (Ex = 30mV, Ey=-75mV, and Ez=-10mV)

EPSP

Which of the following describe differences between EPSPs and action potentials (APs)?

EPSPs decay as they travel, whereas APs do not

Which equation would you use to calculate the resting membrane potential? (circle one) Goldman equation Nernst equation Ohm's Law

Goldman equation

If you want to calculate the resting membrane potential of a neuron, which equation would you use and what information would you need to know?

Goldman's equation; you would need to know the ion concentrations in and out of the cell and the relative membrane permeabilities.

Give a hypothesis that would explain how this mutation in the leak potassium channel changes the resting membrane potential. Explain why this would change the resting membrane potential. (2 sentences max)

If the permeability ratio of Na+:K+ increases, then the resting membrane potential will move towards the Na equilibrium potential, thus depolarizing the cell. The more permeable the neuron becomes to Na, the more it will depolarize toward ENa, according the Goldman equation.

Serotonin Selective Reuptake Inhibitors (SSRIs) are a class of drugs used to treat depression. They work by blocking serotonin reuptake transporters. What effect does this have on serotonergic synapses?

Increases the amount of serotonin in the synaptic cleft, thus prolonging the postsynaptic signal

Explain your answer (1 sentence max).

Itotal = INa + IClBecause magnitude of DFCl > magnitude of DFNa, then magnitude of ICl > magnitude of INaPositive DF means positive ions LEAVE cell or NEGATIVE ions ENTER cell.The large (and positive) DF for Cl means Cl ions go INTO the cell, hyperpolarizing it.

e. If receptor permeability to Na+ is enhanced, the synapse would result in a EPSP

NMI)- likely, but would need to know the relative permeability to say for sure

AMPA Receptors Permeable to: Gating: Ligand:

Na+ K + ligand gated glutamate

NMDA Receptors Permeable to: Gating: Ligand:

Na+ K + Ca+2 ligand gated voltage gated glutamate

Given what you know about how this mutation affects the resting membrane potential, will neurons with this mutation be more or less likely to fire an action potential? Explain your answer. (2 sentences max)

Neurons with this mutation will be more likely to fire an action potential (1.5pts) because the neurons will be closer to threshold at rest (1.5pts).

C. Threshold of voltage-gated Na+ channels is higher

No AP: original depolarizing current was "just enough"

Which of the following statements about G-protein-coupled receptor signaling is TRUE?

One example of amplification is the ability for a single G-protein to activate many enzyme molecules.

If we did not know what the membrane potential was, what other information would we need in order to calculate it?

Pk and PNa (1 pt each) Or permeability of membrane to all ions

Neuropharmacology offers us a powerful tool kit to directly and specifically manipulate the nervous system. Predict the effects of the following drugs on synaptic transmission. Be sure to 1) name the neurotransmitter(s) affected and 2) how the drug would affect the postsynaptic response (e.g. increase, decrease). b) Sertraline (a selective serotonin reuptake transporter inhibitor):

Serotonin would be specifically affected; increase PSP since NT would be in cleft for longer, activating receptors for longer

Your lab has isolated a chemical that speeds up the opening of the voltage-gated K+channels. Draw on top of the action potential on the right to show how the shape of the action potential would or would not change.

Smaller amplitude (potentially skinnier)

Neuropharmacology offers us a powerful tool kit to directly and specifically manipulate the nervous system. Predict the effects of the following drugs on synaptic transmission. Be sure to 1) name the neurotransmitter(s) affected and 2) how the drug would affect the postsynaptic response (e.g. increase, decrease) .a) Bafilomycin (a vesicular proton pump inhibitor):

Synapses using any small molecule NTs- amines and amino acids- would be affected, would likely decrease PSP because less NT would be released and fewer receptors activated

How would you experimentally determine if a neuron was Noradrenergic? You have a very limited budget to do this experiment, so you would like to do so with as few antibodies as possible. You have Tyrosine hydroxylase, Dopa decarboxylase, Dopamine B-hydroxylase, and Phentolamine N-methyltransferase available.

The way to approach this type of problem is to identify the enzymes that are common and unique to the neurotransmitters in each biosynthesis pathway. In the synthesis of catecholamines (dopamine, norepinephrine, and epinephrine), TH is common or required for the synthesis of all 3 neurotransmitters. Antibody staining against TH would thus label cells that were producing any 1 of these 3 neurotransmitters (dopamine, norepinephrine, and epinephrine). We need another antibody to narrow things down further. DBH is common to norepinephrine and epinephrine but NOT dopamine. If were trying to identify noradrenergic neurons vs. adrenergic, we could use antibodies against DBH, but then also stain for PMNT. Cells positive for both markers would be adrenergic. Cells positive for DBH only would be noradrenergic. .

b. Increased dendritic diameter and increased membrane resistance reduce EPSP decay.

True

Name of Phase 5. gNa or gK higher? V-gated Na+ channel state V-gated K+ channel state

Undershoot gK Closed (deinactivated acceptable) Open (Closing acceptable)

In order to beat correctly, heart muscle cells undergo action potentials that have a much longer falling phase than those seen in neurons. Given that neurons and muscles have voltage-gated channels for the same ions and have the same concentration gradients, how might the kinetics of the voltage-gated ion channels be different in heart muscle cells compared to neurons?

V-gated K+ channels open slower

Given the equilibrium potentials below, if we have a neurotransmitter receptor that is selective for X+ and Y+ and conducts them both equally well, which ion would carry the majority of the current through the channel if the channel opens when the membrane potential is -75mV? (Ex = 30mV, Ey=-75mV, and Ez=-10mV)

X+

Given the equilibrium potentials for ions X+, Y+, and Z- below, which direction would each of these ions move (if given the opportunity) at +0 mV? (Ex = 30mV, Ey=-75mV, and Ez=-10mV)

X+ in, Y+ out, Z- in

Given the equilibrium potentials for ions X+, Y+, and Z- below, which of these ions would have the greatest magnitude driving force (if given the opportunity to move across the membrane) at 0 mV? (Ex = 30mV, Ey=-75mV, and Ez=-10mV)

Y+

You are studying a rare neurodegenerative disease that is caused by the mutation of a single protein. You notice that when this mutated protein is expressed, anterograde transport is slowed, but retrograde transport appears to be unaltered. (iii)(2 points) Will the transport of newly synthesized neuropeptides to the synapse be affected by mutations in this disease? (circle your response) Yes No Not enough infomation

Yes

If the NMDA glutamate receptor was mutated so that it was no longer permeable to Ca2+, what would be the effect?

You would see no change in synaptic strength

If we find a drug that can inhibit PNMT, what effect would this have?

decrease the production of epinephrine

4. A typical neuron is made permeable to only Na+ and K+. Assume EK = -80 mV, ENa = +55 mV, and Vm = -65 mV c. If [K+]out increases, the membrane potential of cell will (hyperpolarize/depolarize/not change).

depolarize

If we activate a metabotropic receptor that downstream of its G-protein causes the removal of some leak channels (both Na+ and K+), what effect would this have?

have no effect on the membrane potential and increase the membrane resistance

You discover a new ion channel called Salty that is equally permeable to Na+ and Cl- and impermeable to other ions. You express this channel in a neuron with Vm = -65mV and find that DFNa = -50mV and DFCl = 100mV. When the Salty channel is open, the neuron will (circle one): depolarize hyperpolarize neither

hyperpolarize

To test this hypothesis, you find neurons that express your receptor and only one kind of G-protein (Go). You mutate Go to prevent it from splitting into different subunits. You add neurotransmitter BBB to the synaptic cleft and record from the postsynaptic cell. Next, you make a new mutation in Go so that it cannot hydrolyze GTP. You add neurotransmitter BBB to the synaptic cleft and record from the postsynaptic cell. What do you expect to see? Circle one. Longer hyperpolarization Shorter hyperpolarization No hyperpolarization No change

longer hyperpolarization

Kinesin is a motor protein that attaches to ______________________ to perform ________________________ transport of vesicles and proteins.

microtubules; anterograde

To test this hypothesis, you find neurons that express your receptor and only one kind of G-protein (Go). You mutate Go to prevent it from splitting into different subunits. You add neurotransmitter BBB to the synaptic cleft and record from the postsynaptic cell. i.If your receptor is ionotropic, what do you expect to see, compared to neurons with normal Go? Circle one. Longer hyperpolarization Shorter hyperpolarization No hyperpolarization No change

no change

To test this hypothesis, you find neurons that express your receptor and only one kind of G-protein (Go). You mutate Go to prevent it from splitting into different subunits. You add neurotransmitter BBB to the synaptic cleft and record from the postsynaptic cell. If your receptor is metabotropic, what do you expect to see, compared to neurons with normal Go? Circle one. Longer hyperpolarization Shorter hyperpolarization No hyperpolarization No change

no hyperpolarization

You hypothesize that the receptor is metabotropic because you find it has ______ transmembrane domains. Circle one:

seven

D. # of Voltage-gated K+ channels is reduced

slower falling phase, reduced undershoot

What effect would reducing extracellular Na+ have on the action potential in voltage clamp?

smaller amplitude negative current

Indicate how each of the following would likely change the amplitude of an isolated EPSP from a glutamatergic synapse, which has both AMPA and NMDA receptors. Increase the amount of neurotransmitter in each vesicle

increase

Indicate how each of the following would likely change the amplitude of an isolated EPSP from a glutamatergic synapse, which has both AMPA and NMDA receptors. Increase the conductance of V-gated Ca2+ channels at active zone

increase

B. Leak channels slightly more permeable to Na+, gK still> gNa

increased resting potential

The sign of the PSP observed depends on the receptor's relative permeability to Na+ and K+

T

c. The rate of EPSP decay in the dendrites can be reduced with myelination.

False, dendrites are not myelinated, only axons are.

2. A synapse exists in which the pre-synaptic and post-synaptic cells both sit at -65mV. ENa+ = +50mV and EK+ = -80mV. Imagine that the pre-synaptic cell releases one type of neurotransmitter which is known to bind a single type of receptor. The receptor is transmitter-gated, and it conducts both Na+ and K+. Indicate whether the following statements are true/false/or whether you need more information. Note: think about each manipulation separately, not as each one influencing the next manipulation a. Neurotransmitter binding will result in an EPSP

(NMI)- don't know relative permeability of channel

If the receptor permeability to Na+ is completely eliminated, neurotransmitter binding would result in IPSPs

(T)- if K+ is the only ion Erev=Ek, so the channel would work to make Vm -80

(ii) What point on the graph corresponds to a time within the absolute refractory period? (circle one)

4

(iii) What point on the graph corresponds to a time within the relative refractory period? (circle one)

5

b. Inhibition of second messenger function will eliminate the PSP

F)- not metabotropic

Name of Phase 4. gNa or gK higher? V-gated Na+ channel state V-gated K+ channel state

Falling phase gK Inactivated Open

The membrane potential of the postsynaptic neuron shown here is -65 mV. A, B, C, and D are all GABAergic synapses. For this cell, ECl is -65 mV, EK is -80 mV, and ENa is +60 mV. Synapses A and C have GABAA receptors, which are permeable only to Cl-. Synapses B and D have GABAB receptors, which are metabotropic receptors that open K+ permeable channels. Circle which of these synapses could prevent an EPSP from the labeled excitatory synapse from reaching the axon hillock (more than one possible):

ABD

When the brain is deprived of oxygen, the mitochondria within neurons cease production of ATP. What effect would this have on the membrane potential? Why? Would this be a slow or quick process?

ATP hydrolysis is critical to proper functioning of the Na+/K+ pump in the neuron. This question is really asking us how loss of the pump affects resting potential. Remember that the Na+/K+ pump works to establish concentration gradients across the cell membrane that ultimately determine the equilibrium potentials for Na+ and K+ and the driving force for the movement of each ion. If these gradients are lost, the molar ratio of ions inside and outside the cell will approach 1 (concentrations outside = concentration inside), and the resulting equilibrium potentials of Na+ and K+ will approach 0mV. Since EK is the primary contributor to resting potential ( higher permeability to K+ due to K+ leak channels), the resting potential of the cell will now be more positive (closer to 0mV). However, this will not happen instantaneously, it will take some time for the concentrations on either side of the membrane to deteriorate. The length of time will mostly depend on the permeability of the membrane to both K+ and Na+.

You discover a novel species of organisms in which neurons behave differently from mammalian neurons. At rest, membrane of the neurons is only permeable to Na+. During the generation of an action potential, membrane permeability to Cl- quickly increases until it approximately equals the permeability to Na+. Assuming the equilibrium potentials for Na+ and Cl- are +55mV and -60mV respectively, answer the following questions pertaining to this novel species: a. What is the resting membrane potential of the neurons?

Answer: +55mV. Since the cell is only permeable to Na+ at rest, the resting membrane potential is the same as the equilibrium potential for Na+.

You discover a novel species of organisms in which neurons behave differently from mammalian neurons. At rest, membrane of the neurons is only permeable to Na+. During the generation of an action potential, membrane permeability to Cl- quickly increases until it approximately equals the permeability to Na+. Assuming the equilibrium potentials for Na+ and Cl- are +55mV and -60mV respectively, answer the following questions pertaining to this novel species: What is the direction of the net Cl- flow across Cl- channels during action potential? Explain briefly.

Answer: Inward. To bring membrane potential from +55mV down to a less positive value, negatively charged Cl- ions must move inward.

You discover a novel species of organisms in which neurons behave differently from mammalian neurons. At rest, membrane of the neurons is only permeable to Na+. During the generation of an action potential, membrane permeability to Cl- quickly increases until it approximately equals the permeability to Na+. Assuming the equilibrium potentials for Na+ and Cl- are +55mV and -60mV respectively, answer the following questions pertaining to this novel species: How would the membrane potential change during the generation of an action potential? Why?

Answer: Vm will become less positive and approaches -2.5mV (exactly between the two equilibrium potentials). When the cell is equally permeable to Na+ and Cl-, it will move toward a potential between the equilibrium potential of both of them.

A neuron with a resting potential of -65mV suddenly becomes permeable to a particular type of cation (positively charged ion). If the concentration of the cation is equal on both sides of the membrane, in which direction will the cations flow (into the neuron, out of the neuron, or no flow)? What force(s) would be acting on the cation and in which directions?

Answer: cation will move into the neuron Explanation: Because there is an equal concentration of the cation on either side of the membrane, Ecation=0mV. We are told that the neuron is suddenly permeable to this particular cation, meaning that Vm will want to shift towards Ecation. Because the cation is positively charged and the equilibrium potential wants to make the cell more positive, the cation will want to move INTO the neuron until Vm=0mV, at which point there would be no net movement. In this case, diffusional forces would not be acting on the cation because its concentration is equal on both sides of the membrane, but electrical forces would be acting on it, since the positive charge will be attracted to the negative inside.

You are conducting an experiment to determine how Na+ will move inside and outside of the cell. Indicate in each case the direction of ion movement. ENa= +40 mV Which case (a or b) will the magnitude of the driving force be greater for Na+ ions?

B

Which ion is responsible for the activation of these kinases?

Ca 2+

5 points) You are studying a synapse in which the postsynaptic cell uses G-protein-coupled receptors to signal. When the G-protein is activated, Gα activates a kinase that, when activated, opens a potassium channel. Without an active Gα the kinase and channel will go back to rest. If you mutate the G-protein so that its function changes in the various ways indicated below, what effect will that have on the amount of time it takes for the potassium channel to open and how long the potassium channel will stay open? Fill in the chart using the bolded phrases (each may be used more than once): Gα hydrolyzes GTP much more rapidly

Channel open shorter than normal

5 points) You are studying a synapse in which the postsynaptic cell uses G-protein-coupled receptors to signal. When the G-protein is activated, Gα activates a kinase that, when activated, opens a potassium channel. Without an active Gα the kinase and channel will go back to rest. If you mutate the G-protein so that its function changes in the various ways indicated below, what effect will that have on the amount of time it takes for the potassium channel to open and how long the potassium channel will stay open? Fill in the chart using the bolded phrases (each may be used more than once): G-protein no longer activated by its receptor

Channel won't open at all

5 points) You are studying a synapse in which the postsynaptic cell uses G-protein-coupled receptors to signal. When the G-protein is activated, Gα activates a kinase that, when activated, opens a potassium channel. Without an active Gα the kinase and channel will go back to rest. If you mutate the G-protein so that its function changes in the various ways indicated below, what effect will that have on the amount of time it takes for the potassium channel to open and how long the potassium channel will stay open? Fill in the chart using the bolded phrases (each may be used more than once): Synthesized G proteins localize to ER instead of cell membrane

Channel won't open at all

Microglia

Clearing debris, eliminating any foreign substance CNS

You're studying a new squid neuron that doesn't have any voltage gated ion channels, so all membrane conductance is through leak channels. The leak channels are only permeable to one ion. Vrest= -80 mV. You know the following: Outside Inside K+High Low Y+LowHigh Z-HighLow Cl-LowHigh d.If you wanted to calculate the membrane potential when the cell is expressing the mutated leak channels that conduct also Y+, what information would you need to know?

Concentration of K+ and Y+ both inside and outside out the cell as well as the permeability ratio of PK:PY

9. Why is an excitatory synapse on the soma more effective in evoking action potentials in the post synaptic neuron than an excitatory synapse on the tip of a dendrite?

Currents entering sites of synaptic contact must spread to the spike initiation zone and this zone must be depolarized to threshold for generating an action potential. Depolarization decreases as a function of distance along the dendrite. As a result, the effectiveness of an excitatory synapse for triggering an action potential depends on how far the synapse is from the spike initiation zone, an excitatory synapse on the soma is more effective for evoking action potentials than an excitatory synapse on the tip of a dendrite.

The amplitude of EPSPs degrade as they travel down a dendrite, whereas the amplitude action potentials remains the same as they travel down an axon. (i)(2 points) Name 2 factors that contribute to the degradation of EPSPs as they travel.

Distance from soma, internal resistance (or dendritic diameter), or membrane resistance/conductance

Compare electrical synaptic transmission, chemical synaptic transmission involving ionotropic (transmitter-gated), and chemical synaptic transmission involving metabotropic receptors, with respect to speed and duration. What are the benefits of electrical synaptic transmission?

Electrical synaptic transmission is the fastest form of transmission, ionotropic chemical transmission is the next fastest, and metabotropic chemical transmission is the slowest but with the most long-lasting effects. In addition to being very rapid, electrical transmission is also very reliable and good for synchronizing the activity of groups of neurons.

The advent of electron microscopy allowed scientists to look at cells closer than ever before. How did this discovery finally offer definitive proof of Ramon y Cajal's proposed "Neuron Doctrine"?

Electron microscopic pictures showed that there was a visible gap between neurons at the point where they met, the synapses, proving that neurons are not continuous with each other. This is in accordance with the "neuron doctrine," which proposed that all neurons were, in fact, distinct cells, rather than a continuous network (the prevailing thought at the time).

What was the significance of the Golgi stain being developed?

For the first time could visualize the morphology of whole neurons Only stains select neurons Stains whole cell instead of just cell soma Could begin speculating on the function of neurons based on their morphology Provides evidence for the Neuron Doctrine

If you remove intracellular and extracellular sodium and record in current clamp, do you still get net potassium movement across the membrane when a brief current injection depolarizes the neuron above threshold? Why or why not?

If you eliminate extracellular sodium you will not get potassium current. When you are recording an action potential without controlling the voltage, sodium is needed to depolarize the membrane long enough to activate voltage-gated potassium channels. (NOTE: this assumes a short current injection, similar to what an EPSP would do physiologically, to get the neuron to threshold but not to maintain it at threshold)

a.If you remove intracellular and extracellular sodium during a voltage clamp recording, do you still get net potassium movement across the membrane when the voltage is held above threshold? Why or why not?

If you eliminate extracellular sodium, the potassium current remains because it is due to the opening of v-gated potassium channels. Even though the sodium no longer enters the cell, the depolarized potential still exists because the voltage clamp dictates the membrane potential.

Indicate how each of the following would likely change the amplitude of an isolated EPSP from a glutamatergic synapse, which has both AMPA and NMDA receptors. Eliminate extracellular Mg

Increase

Indicate how each of the following would likely change the amplitude of an isolated EPSP from a glutamatergic synapse, which has both AMPA and NMDA receptors. Increase the conductance of AMPA receptors

Increase

Name 2 ways in which the rate of action potential propagation can be increased.

Increased axonal diameter (or decreased internal resistance), increased membrane resistance, or myelination

Execution by lethal injection is performed by intravenous injection of KCl, which causes cardiac arrest by depolarization of cardiac muscle cells. a. Describe how increased K+ in the extracellular space would depolarize a cell. In your answer indicate the direction in which potassium will flow

Increasing extracellular K+ would decrease the diffusional force, which is the force that drives K+ out of cells. If this is decreased, then the cell will depolarize because the electrical force is acting to keep K+ inside the cell (and still paired with Cl- or some other anion). We don't know for sure if K+ will go in or out (since we don't know the exact concentration), but eventually if there is enough K+ outside then the electrical force will outweigh the diffusional force and K+ will flow in.

Long-term (hours):

Initiation CREB signaling pathway/nuclear transcription factor (1pt), resulting in more synthesis of NT receptors(1pt)

d. If the receptor is equally permeable to Na+ and K+, an EPSP will occur

T)- the driving force on Na+ is greater magnitude, so the current due to Na+ will be greater, and we know it's depolarizing because Ena is positive

You are studying a synapse in which the postsynaptic cell uses G-protein-coupled receptors to signal. When the G-protein is activated, Gα activates a kinase that, when activated, opens a potassium channel. Without an active Gα the kinase and channel will go back to rest. If you mutate the G-protein so that its function changes in the various ways indicated below, what effect will that have on the amount of time it takes for the potassium channel to open and how long the potassium channel will stay open? Fill in the chart using the bolded phrases (each may be used more than once): Gα and Gβγ units dissociate (split apart) more slowly

Longer than normal to open channel

Astrocyte

Maintaining the extracellular space, providing nutrients for neurons, forming BBB CNS

Ependymal Cell

Making and circulating CSF CNS, along the ventricles

Explain your reasoning.

Must demonstrate the understanding that temporal summation arises from the same synapse, but an EPSP and an IPSP can't be produced at the same synapse, so it must be spatial summation

In the human body, both myelinated and unmyelinated axons naturally exist. Compare/contrast the different properties of these two types of axons. A. Speed of propagation

Myelinated axons are faster

Method of propagation

Myelinated axons use saltatory conduction. Unmyelinated axons continue to depolarize the adjacent area of the axon to maintain the depolarization and propagation of the AP.

Oligodendrocyte

Myelination (insulating the axon) CNS

Schwann Cell

Myelination (insulating the axon) PNS

5. One fateful day, a scientist accidentally falls into a vat of radioactive waste and acquires exactly one genetic mutation expressed only in his neurons. As his peer and friend, you decide to help figure out exactly what went wrong. When you depolarize one of his mutant neurons, you observe the resting membrane potential is unchanged but that the mutant action potential looks very different from a normal action potential (see diagram below). a. Could this mutant action potential be caused by a defect in the Na+/K+ pump? Explain (1-2 sentences).

No because the pump is important for setting resting Vm; however, rest is unchanged in the mutant neuron

1. How would the following manipulations alter the shape of an action potential when recorded in voltage clamp (stepping the voltage from -65mV to 0mV)? c. Removal of extracellular Ca2+.

No change

c. Will activation of A and B together likely elicit an action potential in the soma? Why?

No, B will inhibit EPSP from A (shunting inhibition)

5. One fateful day, a scientist accidentally falls into a vat of radioactive waste and acquires exactly one genetic mutation expressed only in his neurons. As his peer and friend, you decide to help figure out exactly what went wrong. When you depolarize one of his mutant neurons, you observe the resting membrane potential is unchanged but that the mutant action potential looks very different from a normal action potential (see diagram below). b. Could this mutant action potential be caused by a mutation in the leak channels? Explain (1-2 sentences).

No, for the same reason as in part (a)

4. Below is a diagram of three synapses onto a cell. The relative conductance and reversal potential (potential that the synapse wants to shift Vm) is indicated on the left. Assume the resting membrane potential is -65mV and the threshold potential for the neuron is -50 mV. a. Will activation of just synapse A likely elicit an action potential in the soma? Why?

No, synapse is too far from soma, small g (conductance) suggests that it has less effect on overall neuronal output, EPSP will likely dissipate as it moves down the dendrite

Indicate how each of the following would likely change the amplitude of an isolated EPSP from a glutamatergic synapse, which has both AMPA and NMDA receptors. Change the concentration of Cl- on either side of the membra

Stay the same

You're studying a new squid neuron that doesn't have any voltage gated ion channels, so all membrane conductance is through leak channels. The leak channels are only permeable to one ion. Vrest= -80 mV. You know the following: Outside Inside K+High Low Y+LowHigh Z-HighLow Cl-LowHigh You do a voltage clamp experiment to try to determine which ion is conducted by the leak channels. You hold the cell at +10mV and observe a positive current. Does this help identify your leak channel ion? Why or why not?

No- in either case you would get a positive current, since positive current is either positive charges moving out (as would be the case for Y+ if Ey= -80mV and the membrane was clamped at +10mV) or negative charges moving in (as would be the case for Z- if Ez= -80mV and the membrane was clamped +10mV)

NMDA receptor activation leads to kinase activation with both immediate and long term effects. (i) Describe these effects (1 sentence each):Immediate (minutes):

Phosphorylation of NT receptors (1pt), resulting in insertion of more NT receptors into the membrane(1pt)

In each of the panels below, to the left is an action potential trace from a normal cell generated by injecting just enough depolarizing current to reach threshold. For each of the questions below, draw what you think an action potential would look like in response to the same current pulse after you experimentally mutate the neuron to yield conditions A-D. The changes should be relative to the typical action potential given to you. Voltage-gated K+ channels open faster

Reduced overshoot, narrower AP

Name of Phase 1. gNa or gK higher? V-gated Na+ channel state V-gated K+ channel state

Rest gK Closed (deinactivated acceptable) Closed

8. You apply ACh and activate nicotinic receptors on a muscle cell. Which way will current flow through the receptor channels when Vm = -60mV? When Vm = 0mV? When Vm = +60mV? Why?

Reversal potential for the nicotinic AChR is 0mV. If Vm = -60mV, current will flow in to try to bring membrane to 0mV, mainly Na flowing in. If Vm = 0mV no net current flow, Na flowing in = K flowing out. If Vm = + 60mV, current will flow out (both Na and K if ENa = +55)

Name of Phase 3. gNa or gK higher? V-gated Na+ channel state V-gated K+ channel state

Rising phase gNa Open Closed (Opening acceptable)

What are SNARE proteins? What is the function of synaptotagmin?

SNARE proteins bring the membrane of the synaptic vesicle and the presynaptic membrane close together. Synaptotagmin is a calcium binding protein in the vesicle membrane. It binds Calcium and produces membrane fusion

5 points) You are studying a synapse in which the postsynaptic cell uses G-protein-coupled receptors to signal. When the G-protein is activated, Gα activates a kinase that, when activated, opens a potassium channel. Without an active Gα the kinase and channel will go back to rest. If you mutate the G-protein so that its function changes in the various ways indicated below, what effect will that have on the amount of time it takes for the potassium channel to open and how long the potassium channel will stay open? Fill in the chart using the bolded phrases (each may be used more than once): Gβγ activates the potassium channel directly

Shorter than normal to activate

Explain the difference between temporal and spatial summation. When is summation necessary to produce an action potential?

Temporal summation occurs when PSPs from the same synapse happen close enough in time to overlap. Spatial summation occurs when PSPs from different synapses overlap in space. Summation is often necessary to evoke an action potential because most EPSPs are not large enough to bring the axon hillock to threshold.

If you stimulate a neuron in the middle of its axon, which direction will the resulting action potential propagate? Why? (assume all of its voltage-gated Na+ channels are in their resting state, i.e., not inactivated!)

The action potential would travel in both directions, both toward the axon terminal and toward the cell soma. This would happen because we are using an electrode to stimulate in the middle of the axon, which means that the voltage-gated sodium channels in both directions are in their resting state and ready to initiate an action potential. This is very different than what happens physiologically, where the action potential is initiated at the axon hillock and only moves toward the axon terminals, due to the inactivation of v-gated sodium channels (during the absolute refractory period) behind newly activate v-gated sodium channels.

AMPA receptors (the main transmitter-gated receptors for glutamate) are equally permeable to sodium and potassium. If the sodium concentration on either side of the membrane were changed so that the driving force on sodium is equal to but opposite the driving force on potassium, what would the net current through open AMPA receptors be?

The net current would be zero. Because the driving forces are equal but opposite, the magnitude of sodium influx will equal the magnitude of potassium efflux and the currents will effectively cancel out so that there is no net flow.

1. How would the following manipulations alter the shape of an action potential when recorded in voltage clamp (stepping the voltage from -65mV to 0mV)? a. Reduced concentration of K+ inside the cell.

The positive current would be reduced

Ionotropic receptors like the nicotinic ACh receptor and the AMPA receptor permit both Na+ and K+ to pass through the channel. As a result the reversal potential for the receptor is 0mV. The GABAA receptor has a reversal potential of -65mV. Describe what is meant by a reversal potential and how it determines whether a synapse is excitatory or inhibitory.

The reversal potential for a channel is the value of membrane potential at which the direction of current reverses from flowing inward to flowing outward. At the reversal potential there is no net current flow. When the channel opens the ion(s) want to bring the membrane potential toward the reversal potential for that channel. For AMPA the membrane potential will move from Vrest toward 0mV, therefore depolarizing, making it easier to reach threshold for and action potential: an excitatory synapse. For GABAA receptor, the membrane will move toward -65, therefore hyperpolarizing and making it harder to reach threshold for an action potential: inhibitory

1. How would the following manipulations alter the shape of an action potential when recorded in voltage clamp (stepping the voltage from -65mV to 0mV)? b. Blockade of voltage-gated Na+ channels.

There would be no negative current.

Explain why action potentials do not degrade as they travel.

They are constantly being regenerated as they travel by the v-gated channels.

Execution by lethal injection is performed by intravenous injection of KCl, which causes cardiac arrest by depolarization of cardiac muscle cells. What would happen to a cell's resting membrane potential if NaCl were injected by mistake?

This would again increase the diffusional force for Na+ going into the cell, but this time won't have as much of an effect, since Na+ is already highly concentrated on the outside of the cell and the cell is not as permeable to Na+ at rest. So it will increase the resting membrane potential if there is enough Na+ to be significant

3. True or false. a. Shunting inhibition requires that the excitatory synapse be positioned upstream (further from soma) of inhibitory synapse.

True, shunting only works is the inhibitory synapse is positioned downstream of the excitatory synapse.

B. Distribution of Voltage-gated Na+ channels on axonal membrane

V-gated Na+ channels are localized to nodes of Ranvier in myelinated axons. They are distributed uniformly throughout the axonal membrane in unmyelinated axons

In a new neurodegenerative disease that you've just discovered you notice that mitochondria accumulate at the axon terminal. You suspect this is due to some sort of disruption in axonal transport. Formulate at least 3 different hypotheses about how axonal transport could be disrupted to cause the accumulation of mitochondria at the axon terminal.

Various answers are possible in any of these categories: --Anything speeding up anterograde transport selectively- speeding up the rate at which kinesin detaches from microtubules/hydrolyze ATP-- Anything slowing down retrograde transport selectively - reduced dynein- slower detaching/hydrolyzing ATP- disruption of dynein interaction with microtubules --Anything selectively disrupting the interaction with mitochondria and dynein - tether region of dynein gone/mutated- interaction site with mitochondria disrupted

You're studying a new squid neuron that doesn't have any voltage gated ion channels, so all membrane conductance is through leak channels. The leak channels are only permeable to one ion. Vrest= -80 mV. You know the following: Outside Inside K+High Low Y+LowHigh Z-HighLow Cl-LowHigh c.If you mutated the leak channels to make them also conduct K+, what do you think would happen to Vrest? Vrest < -80 mV Vrest > -80 mV No change

Vrest > -80 mV One cation (K+) has a pos Eion and one (Y+) has a neg Eion, so they would have a Vrest somewhere bw the 2 Eions

You're studying a new squid neuron that doesn't have any voltage gated ion channels, so all membrane conductance is through leak channels. The leak channels are only permeable to one ion. Vrest= -80 mV. You know the following: Outside Inside K+High Low Y+LowHigh Z-HighLow Cl-LowHigh Which ion could the leak channel be conducting? Explain your reasoning

Y+ or Z-Y+ would have a negative Eion (conc gradient -> leaves the cell -> makes the cell more neg)Z- would have a negative Eion (conc gradient -> enters the cell -> makes the cell more neg)The others would have a positive Eion

d. Will activation of B and C together likely elicit an action potential in the soma? Why?

Yes, C is strong and downstream of B, and B is very weak because of low/no driving force (Vm-Erev)

b. Will activation of A and C together likely elicit an action potential in the soma? Why?

Yes, spatial summation will occur, C is close to soma and has a large conductance thereby contributing greatly to overall neuronal output

To a healthy, high resistance neuron (it doesn't have many leak channels), you supply a depolarizing stimulus (via microelectrode current) and observe an action potential. Next, you apply a drug that immediately inhibits the sodium-potassium pump on the membrane. You supply the same depolarizing stimulus again within 1 minute of applying the drug. Will the cell fire an action potential? Explain why or why not. (1-2 sentences)

Yes. Each action potential only changes the concentration of ions in the cell by <0.01%, such that it would take MANY APs to eliminate the concentration gradient previously established and maintained by the Na/K pump. This drug would only have an effect after many, many action potentials. The pump is not involved in the generation of an action potential. It supplies/maintains the concentration gradients that are used. It would take many APs to eliminate these gradients already set up by the pump.

Which of the following changes during an action potential?

a.Vmb. b.ENa (concentration changes too small when ions flow for AP, so there is no change here) c.Vm and ENa d.Neither Vm nor ENa

Kinesin is a motor protein important for ( retrograde / anterograde )

anterograde

Indicate how each of the following would likely change the amplitude of an isolated EPSP from a glutamatergic synapse, which has both AMPA and NMDA receptors. Block hydrogen pumps

decrease

Indicate how each of the following would likely change the amplitude of an isolated EPSP from a glutamatergic synapse, which has both AMPA and NMDA receptors. Decrease the number of AMPA receptors

decrease

2. You are studying a neuron that has initiated an action potential (AP) that is now racing along its myelinated axon at a steady rate. a. The AP reaches a stretch of axon that is suddenly unmyelinated. What happens to the conduction velocity (speed of the AP) in this portion of the axon (Increases, Decreases, or No Change)? (circle one)

decreases

You are conducting an experiment to determine how Na+ will move inside and outside of the cell. Indicate in each case the direction of ion movement. ENa= +40 mV You hyperpolarize the cell to -80 mV

in

2. You are studying a neuron that has initiated an action potential (AP) that is now racing along its myelinated axon at a steady rate. b. The AP continues along the unmyelinated part of the axon and reaches a part where the diameter of the axon suddenly gets much larger. What happens to the conduction velocity (speed of the AP) in the wider portion of the axon (Increases, Decreases, or No Change)? (circle one)

increases

4. A typical neuron is made permeable to only Na+ and K+. Assume EK = -80 mV, ENa = +55 mV, and Vm = -65 mV a. The driving force for Na+ is (the same/larger/smaller) than the driving force for K+

larger

Treatment with a newly discovered compound X slows the closing of the voltage gated K+ channels. A normal action potential is graphed in red. On the graph below, draw how the action potential would change after treatment with compound X.

longer, and possibly bigger, undershoot

You are conducting an experiment to determine how Na+ will move inside and outside of the cell. Indicate in each case the direction of ion movement. ENa= +40 mV . You depolarize the cell to +50 mV

out

4. A typical neuron is made permeable to only Na+ and K+. Assume EK = -80 mV, ENa = +55 mV, and Vm = -65 mV b. At rest the conductance for Na+ is (the same/larger/smaller) than the conductance force for K+

smaller

An EPSP and an IPSP cancel each other out in a dendrite. This is an example of (circle one): temporal summation spatial summation cannot be determined

spatial summation