Neurobiology 523- SimUText Sections 1-4

what is the stable Vm for a neuron when channels for two different ions are open?

in between the equilibrium potentials for the individual ions

why does the action potential travel faster in the myelinated neuron?

in the myelinated neuron, when Na+ channels open during the action potential, it can lead to the opening of Na+ channels farther away than in the non myelinated neuron

How does lidocaine work?

it prevents the openings of Na+ channels it prevents an action potential from forming --> set Na+ conductance to zero

how does Vm spread along the axon in two neurons --> myelinated neuron vs not myelinated

the Vm signal spreads farther in the myelinated neuron

how does the action potential change as you vary the intensity of the stimulus?

the action potential doesn't change, but at very low stimulus intensities there is no action potential (all or nothing!)

what happens when a region of myelin is eliminated?

the action potential fails to move through the demyelinated region

which conductance increases first?

the action potential starts by depolarizing the neuron Na+

how do two neurons compare --> myelinated neuron vs not myelinated

the action potential travels faster in the myelinated neuron

after K+ ions diffuse across the membrane, will the cell have a net negative or positive charge?

the cell will be negative compared to its surroundings

below the threshold, an action potential is never generated so pain sensation is not transmitted to the brain from this neuron

true

which statement below is TRUE? - when the neuron's interior is negative compared to its exterior, Vm is negative - when the neuron's interior is positive compared to its exterior, Vm is negative - the neuron's interior always has the same amount of change as its exterior

when the neuron's interior is negative compared to its exterior, Vm is negative

what difference do you notice in how vM changes on the left side of the neuron following a light hammer strike (not painful) vs a hard strike (very painful)?

with a harder strike, the left side of the neuron reaches a higher maximum Vm --> with a stronger stimulus transduction results in a faster and larger change in Vm

an action potential in the motor neuron results in which of the following? - release of neurotransmitter from the motor neuron - a contraction lasting for seconds - a brief twitch-like muscle contraction lasting for a few milliseconds - the perception of pain

- release of neurotransmitter from the motor neuron - a brief twitch-like muscle contraction lasting for a few milliseconds MILLISECONDS NOT SECONDS

approx how high must the Vm rise be in order to produce an action potential?

-56 mV --> where the threshold is

what is the Vm for this neuron at rest (a long time after the action potential)?

-66 mV

what is the equilibrium potential for K+ for a stimulated neuron?

-70 mV

what is the most negative membrane potential the cell can have?

-70 mV

approx. how long (in ms) does it take the action potential to reach the far (right) side of the neuron after stimulation?

38 ms

what is the most positive membrane potential the cell can have?

50 mV

which conductance is larger when the neuron is at rest

K+ --> ALWAYS this is because the resting potential is closer to the K+ equilibrium potential than the Na+ equilibrium potential

what statement below is true? - K+ cannot cross the cell membrane directly but can cross the through any channel - K+ can only move through certain channels and these are different channels than for Na+

K+ can only move through certain channels and these are different channels than for Na+

Crime scene: wife suddenly dies --> Vm really high however the neuron doesn't respond to any stimulation no unusual drugs were detected so how was the woman killed?

K+ equilibrium potential is altered --> increased K+ equilibrium potential means making it more positive soo... need to increase the conc outside so that via diffusion ions will move inside in order to increase the conc outside you need to inject a large amount of K+

in this neuron with a Vm of 0 mV (no difference in net charge between inside and outside the cell), which way will K+ move if just the K+ channel were to open?

More K+ would move out of then into the neuron a decrease in Vm

which statements below are TRUE about Vm?

Vm increases as positive charge moves into the cell Vm decreases as positive charge moves out of the cell

what is the effect of Na+ channel inactivation?

Vm rises normally and then falls but does not return to rest

a channel opens on the left side of the neuron when the hammer strikes. what ion moves through this channel based on the Vm change you see?

a positive ion with higher external concentration, like Na+

when does the spinal cord neuron generate an action potential?

after the nociceptor's action potential reaches the end of the nociceptor

if you set Na+ conductance to its maximum value and varied K+ conductance, how would resting potential change?

as K+ conductance increases, the resting potential would get lower

why does the Vm stop changing after a while?

as K+ diffuses out of the neuron, the electrical force attracting K+ ions into the cell grows larger. eventually the electrical forces balance the effects of diffusion

given your answer to the previous question, what happens to K+ ions over time in this neuron? - what prevents the continued diffusion of K+ ions even though there is a large concentration difference across the membrane? --> electrical forces

as the cell becomes more negative, K+ ions are attracted to the inside of the cell

WHY does the above happen?

because Vm does not rise high enough to open Na+ channels on the far side of the demyelinated region

why do you think there is no action potential if K+ channels open very fast (before the Na+ channels)?

because the K+ channels will lower Vm and prevent Na+ from opening

why doesn't Vm return back to -65 mV when the Na+ channels open in response to depolarization?

because the Na+ channels remain open, keeping the Vm near the Na+ equilibrium potential

in terms of Vm, what is the difference between a stimulus below and above threshold?

below threshold, Vm never rises high enough to trigger the opening of many Na+ channels

which DIRECTION can an ion move through its channels in the stimulation?

both (into and out of the cell)

you can feel a hammer slamming into any part of your hand or arm. how might your brain figure out where the pain is coming from?

by determining which nociceptors generate action potentials

if you were to lower the K+ conc inside the cell, without changing the conc outside the cell, how do you think the equilibrium potential for K+ would change?

equilibrium potential would be less negative, because diffusion will result in fewer ions moving out of the cell

which change below can reproduce the behavior of a neuron exposed to snake venom neurotoxin?

maximum K+ conductance is dramatically reduced the toxin works by blocking K+ channels

at the peak of the action potential (highest Vm) is the neuron negatively or positive charged compared to its surroundings?

more positively charged

without the action potential, what happens when the hammer strikes?

near the hammer hit, Vm increases a little and then decreases - the neuron needs some way to transmit this signal over longer distances (the action potential)

during the action potential, is Vm the same everywhere throughout the neuron

no

if the concentrations of both Na+ and K+ are higher inside the cell than outside and Vm is initially 0, is it possible for Vm to be positive after opening channels?

no because diffusion would move positive charge out of the cell

there is more Na+ outside than inside, what do you predict the Na+ equilibrium potential is?

positive, opposite the equilibrium potential of K+

what does botulinum toxin do?

prevents the release of neurotransmitter

as the conc inside a cell increases (for either Na+ or K+) what happens to the equilibrium potential for that ion?

the equilibrium potential becomes more negative because diffusion is going to result in more ions moving out of the cell

what is the best explanation for how the voltage increase from transduction spreads down the axon?

the initial voltage increase causes nearby voltage gated Na+ channels to open. Na+ enters, raising local Vm. This opens more nearby channels, in a chain that spreads down the neuron

how do you think the nociceptor indicates the intensity of pain?

the intensity of pain is indicated by the number of action potentials

what must occur for the muscle fiber to contract more forcefully? (Hint: Recall how the nociceptor indicated stronger stimuli, and use this idea in the stimulation to see if it works)

the motor neuron generates many action potentials in a brief amount of time

what statement below is TRUE when lidocaine is applied to the middle of the nociceptor? - the nociceptor does not respond to painful stimuli. an action potential is never generated. - the action potential is not affected by lidocaine applied to the middle of the nociceptor. lidocaine must be applied near the stimulus point to have an effect - the nociceptor does not release neurotransmitter

the nociceptor does not release neurotransmitter

what is true regarding the nociceptor?

the nociceptor generates action potentials that travel toward the brain

what statement below is TRUE about the shape of the action potential along the axon? --> (as the action potentials are transferring along) - the peak Vm of the action potential decreases as it travels to the right - the peak Vm of the action potential remains about the same as it travels to the right - the peak Vm of the action potential increases as it travels to the right

the peak Vm of the action potential remains about the same as it travels to the right

how does the resting potential change as Na+ conductance increases?

the resting potential gets more positive as Na+ conductance increases until it is midway between K+ and Na+ equilibrium potentials

what statement below is true: - the slower K+ channels close, the longer after hyper polarization lasts - the slower K+ channels close, the taller the action potential - the slower K+ channels close, the longer the action potential lasts - the slower K+ channels close, the slower Vm falls after the peak of the AP

the slower K+ channels close, the longer after hyper polarization lasts

what part of the nociceptor results in an action potential when hit?

the tip of the nociceptor in the finger

if the Na+ conductance is suddenly made much larger than the K+ conductance, which statement below is true? - the vM will shoot above the Na+ equilibrium potential - the vM will approach the Na+ equilibrium potential more closely as the Na+ conductance increases - the vM will always start at the K+ equilibrium potential

the vM will approach the Na+ equilibrium potential more closely as the Na+ conductance increases

what happens after K+ channels have been open for a few milliseconds?

there is no net movement of K+ ions across the membrane (as many moving in as out) and the Vm stops changing