HUMB1000 Lecture Notes - Lecture 9: Depolarization, Saltatory Conduction, Sensory Neuron

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21 Jun 2018

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C8 L3 – Electric Signals and Action

Potentials:

Electrical signals:

- Action potentials

- Membrane potential is the difference in charge across the cell membrane

oThe differences in ionic concentration (Na+ and K+) across the cell membrane and

the permeability of the cell membrane to ions allows for a membrane potential

Membrane ion channels:

- Non-gated ion channels (leak):

oIon specific

oCell membrane has more K+ leak ion channels than Na+ leak ion channels

- Gated ion channels: requires signal to open them

1) Ligand-gated channel (chemical/ligand binds to channel)

2) Voltage-gated ion channel (change in electric charge/action potential)

3) Other-gated ion channel (pressure, temperature, touch)

Resting membrane potential: difference in charge across cell

membrane in a resting cell

- Intracellular side is more negative

- RMP of neurons = - 70mV where negative sign indicates the charge on the intracellular side

of the cell

- RMP caused by leak ion channels and Na+/K+ pump

Changing RMP:

- Depolarisation is when the membrane potential becomes more positive ie. Intracellular

becomes more positive (-70mV to -30mV)

- Hyperpolarisation is when the membrane potential becomes more negative ie. Intracellular

becomes more negative (-70mV to -75mV)

Graded Potential: can lead to action potentials

- Short lived, localised changes in membrane potential

- Often occur in dendrites or cell body of a neuron

- Ability to summate (effect of gradient potential added to effect of another)

- Decremental, not able to transfer information over long distances

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Document Summary

Membrane potential is the difference in charge across the cell membrane: the differences in ionic concentration (na+ and k+) across the cell membrane and the permeability of the cell membrane to ions allows for a membrane potential. Non-gated ion channels (leak): ion specific, cell membrane has more k+ leak ion channels than na+ leak ion channels. Gated ion channels: requires signal to open them: ligand-gated channel (chemical/ligand binds to channel, voltage-gated ion channel (change in electric charge/action potential, other-gated ion channel (pressure, temperature, touch) Resting membrane potential: difference in charge across cell membrane in a resting cell. Rmp of neurons = - 70mv where negative sign indicates the charge on the intracellular side of the cell. Rmp caused by leak ion channels and na+/k+ pump. Depolarisation is when the membrane potential becomes more positive ie. intracellular becomes more positive (-70mv to -30mv) Hyperpolarisation is when the membrane potential becomes more negative ie. intracellular becomes more negative (-70mv to -75mv)

Related Questions

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

HUMB1000 Lecture Notes - Lecture 9: Depolarization, Saltatory Conduction, Sensory Neuron

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