Physio Ex 3 Activity 1,2,3

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

A change in K+ conductance would have a greater effect on the resting membrane potential than a change in Na+ conductance would because the membrane is more permeable to K+.

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

A change in extracellular Na+ results in little change to resting membrane potential because the plasma membrane of a neuron is only slightly permeable to Na+ because it contains relatively few Na+ leakage channels. This inhibits net diffusion of Na+ into or out of the cell. There are less Na leak channels thank K leak channels. Na channels are closed while a neuron is resting

What change in membrane potential (depolarization or hyperpolarization) triggers an action potential?

A depolarization in the membrane potential results in an action potential. The membrane potential must become less negative to generate an action potential.

Explain why increasing extracellular K+ causes the membrane potential to change to a less negative value. How well did the results compare with your prediction?

During the repolarization phase, less K are leaving. This makes the voltage stay more positive, making the neuron take longer to repolarize.

What is meant by the term graded potential?

Graded potentials are brief, localized changes in the membrane potential that can be either depolarizing or hyperpolarizing.

What type of sensory neuron would likely respond to the green light?

Photosensory neurons would respond to green light.

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?

The action potential didn't change as the stimulus voltage increased. This is because once threshold is met, the event is all or none, not graded.

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?

The efflux of potassium ions is maintained by passive potassium channels.

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

The membrane is highly permeable to K because of the amount of K leak channels that are open. The membrane has a low permeability to Na ions because there are very few Na leak channels, and Na channels are closed.

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?

The moderate intensity chemical modality induced a receptor potential of the largest amplitude in the olfactory receptor.

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?

The moderate intensity pressure modality induced a receptor potential of the largest amplitude in the pacinian corpuscle.

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?

The pacinian corupuscle and the free nerve ending are not likely to have the isoamylacetate receptor because they did not respond to chemical stimuli.

What part of a neuron was investigated in this activity?

The trigger zone was investigated. This is where the axon hillock and the initial segment come together.

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

There is usually more K+ inside the cell relative to the extracellular environment. Increasing extracellular K+ reduces the concentration gradient, thus reducing net diffusion of K+.

An action potential is an "all-or-nothing" event. Explain what is meant by this phrase.

This means that once threshold is met an action potential occurs. If the stimulus is too small an action potential does not occur.

Define the term threshold as it applies to an action potential.

Threshold is the voltage that must be reached in order to generate an action potential.

Axons are

long, thin structures that extend from a neuronal cell body