Physio9.0 excercise 3 help!

ACTIVITY #1
1.    Explain why increasing extracellular K+ reduces the net diffusion of K+ out the neuron through the K+ leak channels?
Because when the diffusion is greater on one side, the other side will slow down.

2.   Explain why increasing extracellular K+ causes the membrane potential to change to a less negative value.  How well did the results compare with your predictions?  
There are two potassium’s for every sodium, so the increase of potassium will make it more negative.

3.   Explain why a change in extracellular Na+ did not significantly alter the membrane potential in the resting neuron?
The sodium channels are mostly closed during the resting state.

4.   Discuss the relative permeability of the membrane to Na+ and K+ in a resting neuron.
The sodium is outside, while the potassium is inside. If one diffuses at a higher rate, the permeability changes.

5.   Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential.
A increase in potassium will cause a more negative resting potential.
ACTIVITY #2
1.   Sensory neurons have a resting potential based on the efflux of potassium ions (as demonstrated in Activity 1). What passive channels are likely found in the membrane of the olfactory receptor, in the membrane of the Pacinian corpuscle, and in the membrane of the free nerve ending?
Chemical and pressure channels.

2.   What is meant by the term graded potential?
Graded potential are changes in the transmembrane potential that cannot spread far from the site of stimulus.

3.   Identify which of the stimulus modalities induced the largest amplitude receptor potential in the Pacinian corpuscle. How well did the results compare with your prediction?
High Pressure, my prediction did not change.

4.   Identify which of the stimulus modalities induced the largest amplitude receptor potential in the olfactory receptors. How well did the results compare with your prediction?
High chemicals, my prediction did not change.

5.   The olfactory receptor also contains a membrane protein that recognizes isoamylacetate and, via several other molecules, transduces the odor stimulus into a receptor potential. Does the Pacinian corpuscle likely have this isoamylacetate receptor protein? Does the free nerve ending likely have this isoamylacetate receptor protein?
No.
6.   What type of sensory neuron would likely respond to the green light?
Physical sensory.

ACTIVITY #3
1.   Define the term threshold as it applies to an action potential.
It is the transmembrane potential at which an action potential begins.

2.   What change in membrane potential (depolarization or hyperpolarization) triggers an action potential?
Depolarization
3.   How did the action potential at R1 (or R2) change as you increased the stimulus voltage above the threshold voltage? How well did the results compare with your prediction?
It did not change.

4.   An action potential is an "all-or-nothing" event. Explain what is meant by this phrase.
All stimuli that bring the membrane to threshold generate identical action potentials. The properties of the action potential are independent of the relative strength of depolarizing stimuli.
5.   What part of a neuron was investigated in this activity?
The Axon.
ACTIVITY #4
1.   What does TTX do to voltage-gated Na+ channels?
It irreversibly blocks voltage gated sodium channel in the axonal membranes.

2.   What does lidocaine do to voltage-gated Na+ channels? How does the effect of lidocaine differ from the effect of TTX?
Lidocaine is not always sensitive to the receptors and TTX causes irreversible damage. Lidocaine is slow at reacting and eventually wears off.

3.   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?
No, because not all nerves are sensitive to lidocaine.

4.   Why are fewer action potentials recorded at recording electrodes R2 when TTX is applied between R1 and R2? How well did the results compare with your prediction?
Because it blocked the receptors, therefore it did not work as predicted.

5.   Why are fewer action potentials recorded at recording electrodes R2 when lidocaine is applied between R1 and R2? How well did the results compare with your prediction?
Because of the sensitivity to the drug.
6.   Pain-sensitive neurons (called nociceptors) conduct action potentials from the skin or teeth to sites in the brain involved in pain perception. Where should a dentist inject the lidocaine to block pain perception?
Inferior Alveolar Nerve

ACTIVITY #5
1.   Define inactivation as it applies to a voltage-gated sodium channel.
The channels close which no longer allows sodium ions to enter.
2. Define the absolute refractory period.
It is the first part of the refractory period. The membrane does not respond normally to additional depolarizing stimuli from the point the action potential begins, until the resting potential has been stabilized.

3. How did the threshold for the second action potential change as you further decreased the interval between the stimuli?  How well did the results compare with your prediction?
It needs a lower threshold. The threshold always has minimum and will not decrease.

4. Why is it harder to generate a second action potential during the relative refractory period?
Because it blocked the receptors and therefore it did not work out as I predicted.
It requires a higher stimuli because the threshold is higher.


ACTIVITY #6
1.   Why are multiple action potentials generated in response to a long stimulus that is above threshold?
After one action potential has been generated and the axon is fully recovered from the absolute refractory period. The stimulus is still is still present to generate another action potential.
2.   Why does the frequency of action potentials increase when the stimulus intensity increases? How well did the results compare with your prediction?
When the stimulus intensity increases, it will generate a great frequency of action potentials.
3.   How does threshold change during the relative refractory period?
The threshold doesn’t change during the relative refractory period because, there is no stimulus.
4.   What is the relationship between the interspike interval and the frequency of action potentials?
The relationship between the two, is that every time you decrease the ISI, the frequency of the action potential will increase.

ACTIVITY #7
1.   How did the conduction velocity in the B fiber compare with that in the A Fiber? How well did the results compare with your prediction?
The B fiber will react slower since it is less mylinated.
2.   How did the conduction velocity in the C fiber compare with that in the B Fiber? How well did the results compare with your prediction?
The C fiber was much slower to respond because it has no mylination. My prediction did not change.
3.   What is the effect of axon diameter on conduction velocity?
If the axon has a larger diameter, the conduction goes faster.
4.   What is the effect of the amount of myelination on conduction velocity?
Having a large mylinated diameter makes it go faster.
5.   Why did the time between the stimulation and the action potential at R1 differ for each axon?
Because of the amount of mylination on the axons.
6.   Why did you need to change the time scale on the oscilloscope for each axon?
You wouldn’t be able to see the action potential if the times stayed the same.
ACTIVITY #8
1.   When the stimulus intensity is increased, what changes: the number of synaptic vesicles released or the amount of neurotransmitter per vesicle?
The number of synaptic vesicles increases with the intensity
2. What happened to the amount of neurotransmitter release when you switched from the control extracellular fluid to the extracellular fluid with no Ca2+ ? How well did the results compare with your prediction?
No transmitters were released.
3. What happened to the amount of neurotransmitter release when you switched from the extracellular fluid with no Ca2+to the extracellular fluid with low Ca2+ ? How well did the results compare with your prediction?  You did not answer this question.
Only a few were released with low Ca2+, and went along with my prediction.
4. How did neurotransmitter release in the Mg2+ extracellular fluid compare to that in the control extracellular fluid? How well did the result compare with your prediction?
Mg2+ released a very small amount of neurotransmitters.
5.   How does Mg2+ block the effect of extracellular calcium on neurotransmitter release?
Mg2+ is more of a blocker and over powers the calcium.

ACTIVITY #9
1. Why is the resting membrane potential the same value in both the sensory neuron and the interneuron?
The sensory and interneurons were both at resting potential, so there was nothing to stimulate it.
2. Describe what happened when you applied a very weak stimulus to the sensory receptor. How well did the results compare with your prediction?
A very small response in the R1 receptor, and no response in the rest.
3. Describe what happened when you applied a moderate stimulus was to the sensory receptor. How well did the results compare with your prediction?
All of them had a response and R1 and R3 had the largest graded potential.
4. Identify the type of membrane potential (graded receptor potential or action potential) that occurred at R1, R2, R3, and R4 when you applied a moderate stimulus (view Experiment Results to view the response to this stimulus).
Graded Receptor Potential
5. Describe what happened when you applied a strong stimulus to the sensory receptor. How well did the results compare with your prediction?
The action potential was that much stronger from the other amounts of stimuli.

Not sure if these are correct. But I hope this helps.

56.   Describe what happened when you applied a very weak stimulus to the sensory receptor, i.e. was there an action potential?  How many vesicles were released?

When you applied a very weak stimulus to the sensory receptor, a small, depolarizing response occurred at R1, and no responses occurred at R2, R3, and R4.

While I appreciate the help, aren't all of these answers incorrect? When I just did the activity, all my data is showing that the unmylinated axons have faster conduction velocities. So A fibers would have the slowest conduction velocity and the C fibers would be the fastest.

It could be, what was the exact question you needed to answer?

Here is what I got, copied from my pdf

Experiment Results
Predict Question:
Predict Question 1: How will the conduction velocity in the B fiber compare with that in the A Fiber?
Your answer : b. The conduction velocity in the B fiber will be slower because the B fiber has a smaller diameter and less
myelination.
Predict Question 2: How will the conduction velocity in the C fiber compare with that in the B Fiber?
Your answer : d. The conduction velocity will be the same in both fibers.
Stop & Think Questions:
3. Note the difference in time between the action potential recorded at R1 and the action potential recorded at R2. The
distance between these sets of recording electrodes is 10 centimeters (0.1 m).
Convert the time from milliseconds to seconds, enter the time (in seconds) in the field below, and then click Submit to
display your results in the grid.
You answered: 0.002 sec
4. Calculate the conduction velocity in meters/second by dividing the distance between R1 and R2 (0.1 m) by the time it took
for the action potential to travel from R1 to R2.
Enter the conduction velocity in the field below and then click Submit to display your results in the grid.
You answered: 50 m/sec
7. Note the difference in time between the action potential recorded at R1 and the action potential recorded at R2.
Convert the time from milliseconds to seconds, enter the time (in seconds) in the field below, and then click Submit to
display your results in the grid.
You answered: 0.01 sec
8. Calculate the conduction velocity in meters/second by dividing the distance between R1 and R2 (0.1 m) by the time it took
for the action potential to travel from R1 to R2.
Enter the conduction velocity in the field below and then click Submit to display your results in the grid.
You answered: 10 m/sec
11. Note the difference in time between the action potential recorded at R1 and the action potential recorded at R2.
Convert the time from milliseconds to seconds, enter the time (in seconds) in the field below, and then click Submit to
display your results in the grid.
You answered: 0.1 sec
12. Calculate the conduction velocity in meters/second by dividing the distance between R1 and R2 (0.1 m) by the time it
took for the action potential to travel from R1 to R2.
Enter the conduction velocity in the field below and then click Submit to display your results in the grid.
You answered: 1 m/sec
Experiment Data:

In the activity my data is:
A fiber is large in diameter but heavily myelinated,  it came out with a conduction velocity of 50 m/sec, B fiber is a medium diameter with thin myelination with conduction velocity of 10 m/sec and the C fiber is a thin diameter with no myelination and its conduction velocity is 1 m/sec.

So specifically the way these were answered are not matching up with my data.


Even though the A fiber had a larger axon diameter, it was also heavily myelinated so the size of the axon didn't make it faster, it actually made it slower than the thinnest axon diameter (fiber C).

Then for question #4, wouldn't it be that the less myelination on an axon, the faster the conduction velocity?

Look at the numbers. 50m/sec is faster than 1m/sec.

  thanks!!

Thanks for this, has helped me understand things better!!

Hope this helps someone!

This has been very helpful

Post Merge: 11 years ago

This has been very helpful

These are the answers I got from Exercise 3 on PhysioEX 9.0.  Hope this helps someone!!


Eliciting (Generating) a Nerve Impulse
1.    Why don't the terms depolarization and action potential mean the same thing?
A depolarization is any change in a neuron that makes it more positive than resting potential, but an action potential only occurs when the depolarization reaches the threshold level.

2.    What was the threshold voltage in Activity 1?
3.0 V

3.    What was the effect of increasing the voltage? How does this change correlate to changes in the nerve?
There was a slight increase

4.    How did the action potential generated with the unheated rod compare to that generated with the heated rod?
The action potential generated with the unheated rod was less than the action potential generated by the heated rod.

5.    Describe the types of stimuli that generated an action potential.
Electrical, mechanical, thermal, and chemical stimuli are all capable of generating an action potential.

6.    If you were to spend a lot of time studying nerve physiology in the laboratory, what type of stimulus would you use and why?
Although many different stimuli work, electrical stimulators are convenient because the voltage duration and frequency of the shock can be very precisely set for use.

7.    Why does the addition of sodium chloride elicit an action potential? Hint: Think about the sodium permeability of the neuron (Figure 3.2e).
While the sodium-potassium pump is pumping sodium out of the cell and potassium into the cell, these ions are leaking back where they came from by diffusion. By adding sodium chloride, a more-than-normal amount of sodium will diffuse into the nerve, causing the resting membrane potential to reach the threshold value, bringing about a membrane depolarization.

Inhibiting a Nerve Impulse
8.    What was the effect of ether on eliciting an action potential?
 There was no effect it conducted the same

9.    Does the addition of ether to the nerve cause any permanent alteration in neural response?
 No, the ether has no lasting effect.

10.    *What was the effect of curare on eliciting an action potential?
   There is no effect. It inhabits action potential because curare is a toxin.

11.    *Explain the reason for your answer to question 10 above.
      Curare works by blocking synaptic transmissions so that neural impulses do not travel from neuron to neuron. The detached nerve which we are experimenting with does not have any synapses to be blocked. In a living animal, however, curare will kill, as neural impulses cannot jump synapses to allow the heart to work or the animal to breathe.

12.    *What was the effect of lidocaine on eliciting an action potential?
   It blocks sodium ion channels from opening, inhibiting action potentials. There is no action potential when blocked.

Nerve Conduction Velocity
13.    What is the relationship between size of the nerve and conduction velocity?
A larger nerve will have a faster conduction velocity.

14.    Keeping your answer to question 13 in mind, how might you draw an analogy between the nerves in the human body and electrical wires?
Larger electrical wire has less resistance to current flow and will conduct faster than smaller wire with increased resistance to current flow.

 15.    How does myelination affect nerve conduction velocity? Explain, using your data from Chart 1.
 Myelination speeds up nerve conduction velocity by causing the nerve impulse to jump across the cell membrane from one internode to another rather than be conducted across the entire cell membrane.

16.    If any of the nerves used were reversed in their placement on the stimulating and recording electrodes, would any differences be seen in conduction velocity? Explain.
No. Once a neural membrane is depolarized and the impulse is being conducted along the neural membrane, which direction is which does not matter. We state that a neural impulse is set up in the neuron's trigger zone (mainly due to the large number of sodium channels there) but once the depolarization is set up, it not only travels down the axon but also around the soma of the cell.