01:119:116 Lecture Notes - Lecture 19: Extracellular Fluid, Facilitated Diffusion

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lilacguinea-pig158

11 Aug 2018

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Change in membrane potential: action potential= depolarization reaches the threshold (-55mv, na+ rushes in massive change in voltage, action potential= +35mv. Voltage gated ion channels: (na+ and k+, gate opens when a membrane depolarizes, facilitated diffusion- no atp, pic- how voltage gated ion channels work. Before we go on: neuron at rest= no signal, stimulus (what could that be?) Voltage gated na+ and k+ channels closed. For each stage, watch na+ and k+ channels. A few voltage gated na+ channels open. Stronger stimulus= more na+ channels open faster change. If membrane does not reach threshold (-55mv) stays at rest. Is membrane reaches threshold (-55mv) action potential: rising phase- depolarization, falling phase- membrane repolarized. Voltage spikes to +35 mv= max na+ permeability at this point the voltage gated channel is closed for na+ K+ channels closed (they start to open at +30mv) Inside of cell is positive (+) to outside of cell.

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This is the peak depolarization in an action potential. At this point in an action potential two events start to happen.

1. Na+ channels begin to inactivate, which is equivalent to closing.

2. A majority of the K+ channels are beginning to open.

Determine what happens to the membrane potential when voltage-gated K+ channels are open simultaneously with voltage-gated Na+ channels (and the leak K+ channels which are still open). Increase the membrane permeability to K+ by increasing it to 115.

i. What happens to the membrane potential Em? __________________________

j. Why does the membrane potential change in this direction? __________________________ Now inactivate the voltage-gated Na+ channels by reducing the membrane permeability for Na+ back to 1. k. What is the new membrane potential? _____________

l. Is the new membrane potential less negative or more negative than the resting membrane potential listed in line âbâ of this section? _____________

m. Why? (hint: what 2 types of K+ channels are open now?) n. Under the current ionic concentrations given, what is the most negative value that the membrane potential could reach? _____________ (Increase the permeability of the membrane to K+ to confirm your answer.)

o. What equilibrium potential has the same value? _____________

p. At this point in the action potential, when the membrane potential is more negative than the resting potential, the membrane potential is said to be hyperpolarized. What happens to voltage-gated K+ channels (membrane permeability to K+) to bring the membrane potential back to its resting potential near -70mV?_____________

When the membrane potential became more negative than the Threshold potential, the inactivated voltage-gated Na+ channels became reactivated. After the voltage-gated K+ channels closed to enable the membrane potential to return to resting membrane potential they became ready to open again. Both channels are ready to open again in order to fire another action potentia

sapphirepanda54

6. Consider the presence of hemoglobin in the catheter bag. Whatsymptom would this loss of

hemoglobin most strongly and immediately be linked to in thepatient?

A. Loss of blood volume

B. Loss of heartbeat

C. Drop in blood oxygen saturation

D. Liver failure

When a neuron is stimulated, the area of the membrane at thepoint of stimulation becomes

more permeable to Na+. If a cell starts at resting potential(-70mv), and is then stimulated:

A. The membrane voltage will become < -70mV, because Na+will move OUT of the cell.

B. The membrane voltage will become > -70mV, because Na+will move OUT of the cell.

C. The membrane voltage will become < -70mV because Na+will move INTO the cell.

D. The membrane voltage will become > -70mV because Na+will move INTO the cell.

. At the peak of the action potential, the Na+ voltage-gatedchannels close, and K+ voltage-gated

channels open in response to the positive membrane potential.In order to return the cell to its

negative resting potential quickly:

A. K+ will diffuse along its concentration gradient INTO thecell.

B. K+ will diffuse along its concentration gradient OUT of thecell.

C. Na+ will reverse its direction of diffusion OUT of thecell.

D. The sodium-potassium pump will move Na+ OUT of the cell andK+ INTO the cell.

E. None of the above would return the cell to its negativeresting potential quickly.

You experiment with higher concentrations of toxin and findcases when the cell could not

repolarize at all or, if it began to repolarize, itimmediately depolarized again. This tells you that

the toxin:

A. Prevents voltage-gated K+ channels from opening.

B. Increases the speed that the Na+ ion channels open.

C. Prevents the Na+ ion channels from closing.

D. Makes the Na+ ion channels close too soon.

E. Doesn

lavenderclam549

Many ion channels are not normally open but must be gated oropened by some event. Which of the following is NOT a typical meansof opening ion channels?

Select one:

a. Binding of neurotransmitter to external binding site

b. Change in voltage across the membrane

c. Enzymatic reactions

d. Phosphorylation by an intracellular second messenger

Summation of local potentials can lead to a(n) _______ at theaxon hillock if the _______ is reached.

Select one:

a. equilibrium potential; threshold

b. local potential; equilibrium potential

c. action potential; equilibrium potential

d. action potential; threshold

The Na+/K+ pump helps to maintain the _______ by moving threeNa+ ions in and two K+ ions out of the cell.

Select one:

a. action potential

b. resting membrane potential

c. threshold

d. local potential

ochremouse799

01:119:116 Lecture Notes - Lecture 19: Extracellular Fluid, Facilitated Diffusion

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