The Action Potential - I

Question 1

Three types of cells with APs?

Answer 1

Neurons, Muscle, and Neuroendocrine cells

Question 2

How was resting potential determined?

Answer 2

Cell kept in an electrolyte solution. Using glass micropipettes as electrodes, measure on either side of the cell membrane. When one is inserted, steady -60mV is read.

Question 3

What is resting potential?

Answer 3

-60mV

Question 4

What will adding a negative current do to the membrane potential?

Answer 4

Hyperpolarization – Electrotonic Hyperpolarization, proportionally

Question 5

What will adding a positive current do to the membrane potential?

Answer 5

Inside of cell become positive (depolarization).
Small enough, its proportional
If sufficient, you hit threshold and trigger AP

Question 6

Amplitude of the voltage changes with stimulus is proportional to…. (2 things)

Answer 6

Applied Current

Input Resistance

Question 7

T of F. An AP is graded in size depending on the size of the stimulus.

Answer 7

F. An AP is an all-or-none phenomenon

Question 8

List the 5 characteristics of an Action Potential.

Answer 8

1. Triggered By Depolarization
2. All or None
3. Regenerative and Propagates
4. Have Overshoot and Undershoot
5. Has Absolute Refractory Period

Question 9

While the amplitude of action potentials is constant, the _________ of APs can vary from stim to stim.

Answer 9

Frequency.

Question 10

What do I mean when I say a potential is regenerative and propagates.

Answer 10

At the end of the line its the same signal it was at the beginning

Question 11

What is the Overshoot of an AP?

Answer 11

At the peak of AP whn the mem pot reverses sign and becomes positive

Question 12

What is the undershoot of an AP?

Answer 12

As the potential comes back down it becomes more negative than normal.

Question 13

What is the absolute refractory period?

Answer 13

A period in which it is impossible to make the neuron fire another AP.

Question 14

What did Hodgkin and Huxley do in their studies?

Answer 14

Use the voltage clamp to dissect and characterize the permeability changes associated with AP

Question 15

What does a voltage clamp let you do?

Answer 15

Control the membrane potential at a desired level while measuring current necessary to maintain potential.

Question 16

How did Hodgkin and Huxley’s experiments work?

Answer 16

Place an electrode inside the cell to measure mem pot. and compare to command voltage. Amount of current necessary to maintain mem pot at the command volt is measured.

Question 17

How might Hodgkin and Huxley’s experiments be modernized?

Answer 17

Cell patch clamp recording
(Electrode sealed to cell membrane
Vm and I for Vc is recorded/injected

Question 18

What is a capacitive current?

Answer 18

A brief redistribution of charge across the membrane.

Question 19

When Vm is hyperpolarized, what is seen?

Answer 19

A brief capacitive current, then very little current flows

Question 20

When Vm is depolarized, what is seen?

What does this establish?

Answer 20

A brief capacitive current, then rising inward ionic current (+ entering cell), then a delayed outward current.

Establishes that membrane permeability is voltage dependent

Question 21

Describe the shape of the early current.

Answer 21

First increases, then decreases as depolarization increases. Current reverses back at higher membrane potentials.

Question 22

Why is there no longer any inward current in the cell when Vm is clamped at 55mV? What does this mean?

Answer 22

According to Nernst, 55 is Na’s equilibrium potential. At 55 there will no longer be a net flux of Na across the membrane.

Strongly suggests that inward current is carried by Na.

Question 23

What did the ionic substitution experiment entail? What did it show?

Answer 23

90% reduction in external sodium eliminates the early inward current. It enforces the idea that Na carries the early inward current.

Question 24

How have pharmacological studies reinforced the belief in the roles of K and Na

Answer 24

Using toxins that specifically block Na show a loss of inward current. Toxins that blow K show a loss of outward current.

Question 25

What nerotoxin blocks Na+ currents?

Answer 25

Tetrodotoxin

Question 26

What neurotoxin blocks K+ currents?

Answer 26

Tetraethylammonium

Question 27

Describe the cellular mechanisms associated with seizure disorders.

Answer 27

Leaky Na channels causing fluctuating voltage cause strings of unwanted AP

Question 28

How do you treat seizures?

Answer 28

Dilantin

Question 29

What is hyperkalemic Periodic Paralysis?

Answer 29

Heightened K causes Na channels to shut down.

Treat with Glucose and Ins to drive K into the cells

Question 30

What is hypokalemic periodic paralysis?

Answer 30

Can occur with rest after strenuous activity. Decreased K means No AP possible.