Physioex 3: Neurophysiology

What is the approximate concentration of K+ inside a typical cell (intracellular concentration)?

What is the approximate concentration of K+ outside a cell (extracellular concentration)?

What is the approximate concentration of Na+ inside a cell (intracellular concentration)?

What is the approximate concentration of Na+ outside a cell (extracellular concentration)? 150 mM

What is the polarity of the resting membrane potential (voltage)?

What does it mean that the voltage just inside the membrane is negative?

The membrane of most cells, including neurons, contains passive, open, K + leak channels. Given the normal K+ concentrations and the resultant concentration gradient, which direction would K + be expected to move (diffuse) through these leak channels?

Predict what will happen to the resting membrane potential if the extracellular K+ concentration is increased

What effect does increasing extracellular K+ have on the net diffusion of K+ out of the cell?

Which way would Na+ move across the membrane if there were open Na+ channels?

The membrane has open K+ channels, and changing extracellular K+ concentration results in a change in membrane potential. Changing the extracellular Na+ concentration does not significantly change the membrane potential. What do your results suggest about the number or state (open or closed) of Na+ channels in the resting membrane of a neuron?

A negative membrane potential was recorded when the tip of the microelectrode was

Which of the following caused a change in membrane potential from -70 to -40 in the cell body?

Which of the following has the most negative voltage? - between the outside of the axon and outside the cell body with a control K+ EFC - between the outside of the axon and outside the cell body with High K+ EFC - between the inside of the axon and outside the axon with a control K+ EFC - between the inside of the axon and outside the axon with High K+ EFC

Explain why increasing extracellular K+ reduces the net diffusion of K+ out of the neuron through the K+ leak channels.

Explain why increasing extracellular K+ causes the membrane potential to change to a less negative value.

Explain why a change in extracellular Na+ did not alter the membrane potential in the resting neuron.

Discuss the relative permeability of the membrane to Na+ and K+ in a resting neuron.

Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential.

The adequate stimulus for a Pacinian corpuscle is pressure or vibration on the skin. Which of the following modalities will induce the largest amplitude receptor potential in the Pacinian corpuscle

Why didn't the Pacinian corpuscle respond to high-intensity light?

The adequate stimuli for olfactory receptors are chemicals, typically odorant molecules. Which of the following modalities will induce the largest amplitude receptor potential in the olfactory receptor?

Judging from these results, does light have a smell?

Axons are

An action potential is usually initiated in an axon at or near

The initiation of an action potential in a sensory neuron in the body normally

Why is the action potential recorded by the second recording electrode (R2) delayed relative to the action potential recorded by the first recording electrode (R1) the action potential had to propagate from R1 to R2

How will the action potential at R1 (or R2) change as you continue to increase the stimulus voltage

An increase in extracellular K+ would depolarize a neuron. This depolarization would occur if neurons were damaged. From what you have just learned about generating an action potential, what effect would this have on nearby axons? The nearby axonal membranes will ___________.

The threshold voltage in an axon is usually

If a graded receptor potential made the resting membrane potential of the axon more negative for example, -70 mV), you would expect

Failure to reach the threshold voltage in the axon of a sensory neuron could be caused by

Why did the free nerve ending respond to several different modalities?

A very intense stimulus can sometimes stimulate sensory neurons that have evolved for a different modality. Thus, with a blow to the eye, one "sees stars." In this example the photoreceptors in the eye are responding to

Olfactory receptor neurons respond to low concentrations of chemical odorants because there are membrane proteins in the receptor ending of this sensory neuron that

The sequence of events starting with a sensory stimulus and ending with a change in membrane potential is called

Starting at a resting membrane potential of -70 mV, a change to which of the following represents the largest receptor potential?

Assuming that the resting potential of a sensory neuron is -70 mV, which of the following represents a depolarization?

Which of the following is a sensory modality (type of sense)?

Which of the following is a sensory stimulus?

Which of the following is true of the response of a sensory neuron to the appropriate sensory stimulus?

An action potential can be propagated along an axon because there are __________ channels in the membrane.

The units of conduction velocity are

Which of the following will affect axonal conduction velocity?

Which of the following describes an A fiber?

Which of the following describes a C fiber?

Action potential conduction velocity is fastest in which of the following fibers?

Action potential conduction velocity is slowest in which of the following fibers?

Why did the timescale have to be changed to measure the conduction velocity of the C fibers?

The axons from touch fibers are A fibers, and the axons from pain fibers are C fibers. When you stub your toe, which would you expect to perceive first?

The end of the axon where it contacts a target is called the

Neurotransmitter is released into the synaptic gap by

Exocytosis of neurotransmitter from the axon terminal is triggered by an increase in the intracellular concentration of

Neurotransmitter released into the synaptic gap reaches the target cell by

At the target, neurotransmitter

Why does the stimulus intensity affect the amount of neurotransmitter release at the axon terminal?

solution?

Why did the high intensity stimulation fail to trigger the same amount of neurotransmitter release in the presence of extracellular Mg2+ as in the control extracellular solution?

Sensory neurons respond to an appropriate sensory stimulus with a change in membrane potential that is

If the depolarization that reaches the axon is large and suprathreshold, the result in the axon is

At the axon terminal, each action potential causes the release of neurotransmitter. This neurotransmitter diffuses to the receiving end of an interneuron, where it binds to receptors and causes

Interneurons respond to chemical (neurotransmitter) stimulation with a change in membrane potential that is

Voltage-gate Na+ channels are membrane channels that open

When open, Na+ channels allow

Which of the following can reduce the likelihood of an action potential? a. TTX b. lidocaine c. increasing the leak of K+ from a cell d. All of these can reduce the likelihood of an action potential

With a slower timescale, the appearance of the action potentials generated at R1 and R2 will appear to

Why do you think TTX is not used during dental procedures?

In the control, the amplitudes of the action potentials at R1 and R2 are the same. - there are voltage-gated Na+ channels along the axon - The action potential is an all or none event - action potentials propagate or remake themselves at each point along the axon

Blocking the voltage-gated Na+ channels between R1 and R2 with TTX blocks

When voltage-gated Na+ channels between R1 and R2 are blocked with TTX, an action potential is still recorded at R1 because

Puffer fish must be prepared carefully and properly before they can be eaten. Eating puffer fish can cause numbness of the lips, probably because

What does TTX do to voltage-gated Na+ channels?

What does lidocaine do to voltage-gated Na+ channels? How does the effect of lidocaine differ from the effect of TTX?

A nerve is a bundle of axons, and some nerves are less sensitive to lidocaine. If a nerve, rather than an axon, had been used in the lidocaine experiment, the responses recorded at R1 and R2 would be the sum of all the action potentials (called a compound action potential). Would the response at R2 after lidocaine application necessarily be zero? Why or why not?

Which of the following occurs after the peak of the action potential? a. the membrane repolarizes b. voltage-gated K+ channels open c. some voltage-gated Na+ channels inactivate d. all of these occur

What is meant by Na+ channel inactivation?

What happens when voltage-gated K+ channels open? a. K+ ions can diffuse out of the cell b. the membrane repolarizes from the peak of the action potential c. it becomes harder for a subsequent stimulus to depolarize the membrane to threshold d. all of these occur

it is harder to generate a second action potential soon after the first action potential because a. some voltage-gated Na+ channels are inactivated b. voltage-gated K+ channels have opened c. the efflux of K+ ions opposes a depolarization toward threshold d. all of these make it harder to generate a second action potential

Threshold can be defined as the minimum voltage needed to generate an action potential. Is the threshold for the first action potential the same as, or different from, the threshold for the second action potential with a 60 msec interval?

What is the original threshold for this neuron?

As the interval between stimuli decreases, the depolarization needed to generate the second action potential

Judging from your results, what time period after the first action potential best describes the relative refractory period(the time when a second action potential can be generated only if the stimulus intensity is increased)?

At what interval between stimuli did the second action potential fail, regardless of the stimulus intensity?

What is the absolute refractory period for this neuron?

The time after an action potential when a second action potential cannot be generated no matter how intense the stimulus is called the

The time after an action potential when a second action potential can be generated only if the stimulus intensity is increased is called the

The term frequency refers to

The purpose of this activity is to explore

would be observed?

With a prolonged stimulus that is just above (more depolarized than) threshold, you would expect to get additional action potentials when the membrane has completed

Which of the following changes occurs when you increase the stimulus intensity?

The absolute refractory period is about 3.75 msec. What intensity stimulus would produce action potentials with this interspike interval?