Action Potential and Stimulus Essay

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Ch 11 Answers to # 1-7. ANSWERS ARE IN RED.

1. Look at slide 21 in Ch 11. You are looking at the order of events in Neural Signaling (how a neuron sends a signal).

List the order of events.
1. Resting Membrane Potential
2. Stimulus
3. Graded Potential (if strong enough)
4. Action Potential
5. Synaptic Activity

2. a. What is Resting Membrane Potential. (define it)
It is the transmembrane potential of a cell at rest
All neural activities begin with a change from resting potential

b. Where is K+ higher when the neuron is at rest? (ECF or ICF)
c. Where is Na+ higher when the neuron is at rest? (ECF or ICF)
d. What is (approximately) the voltage (in mV) of a neuron at rest?
About -70mV

3. This is showing you the channels and pump responsible for maintaining Resting Membrane Potential.

a. Describe 1-5.
1. The cytosol contains an abundance of negatively charged proteins, whereas the extracellular fluid contains relatively few. These proteins cannot cross the plasma membrane.

2. Transmembrane Potential is –70 mV with the minus sign indicating that the interior is negatively charged

3. Potassium ions (K+) can diffuse out of the cell through potassium leak channels.

4. The sodium–potassium (Na+/K+) exchange pump ejects 3 Na+ for every 2 K+ recovered from the extracellular fluid. At a transmembrane potential of –70 mV, the rate of
Na+ entry versus K+ loss is 3:2, and the exchange pump maintains a stable resting potential.

5. Sodium ions (Na+) can diffuse into the cell through sodium leak channels.

4. a. Look at slide 42-49. What is a Graded Membrane Potential?

Changes in transmembrane potential that cannot spread far from stimulation site

-Where does it occur in the neuron? Axon Hillock or cell body “soma”

b. If the stimulus is stronger, will that be reflected in the graded potential?
YES! A graded potential reflects the strength of the stimulus!
This means if you touch a warm cup of coffee (lesser stimulus) the inside of the neurons in your hand become less positive (have a lesser graded potential) than if you put your hand on a hot stove (greater stimulus)- if you did this (DON’T DO THIS  ) the neurons in your hand become very positive and a greater graded potential occurs.

c. Define: Depolarization, Repolarization, and Hyperpolarization.
Depolarization: Positively charged ions entering the cell (usually Na+) (becomes more +) DEPOLARIZATION MEANS TO BECOME MORE POSITIVE IN CHARGE

Repolarizition : With removal of chemical stimulus, membrane returns to resting potential because Na+ is lowered (becomes more -) REPOLARIZATION MEANS TO BECOME MORE NEGATIVE IN CHARGE (BACK DOWN TO the RMP of -70mV)

Hyperpolarization: Potassium ions leave cytoplasm Results in more negative transmembrane potential (Becomes even more – than the RMP of -70mV)
HYPERPOLARIZATION MEANS TO BECOME EVEN MORE NEGATVIE IN CHARGE (-80mV- more negative than RMP)

c. Look at slide 50. What are the 4 characteristics of a Graded Potential?

(I broke these down in my own words- there are many ways to say this correctly so please don’t worry if your answers were different than mine)

- the transmembrane potential (or change in charge in the neuron) is most affected at the site of stimulation and decreases the further you get from the site of stimulation

-the effect (influx of Na+) will occur passively through the soma “cell body”

-the change in charge inside the cell depends on whether positive ions are entering or leaving. So if Na+ ENTERS then the change in charge (transmembrane potential) becomes more positive = Depolarization…BUT is K+ Leaves the cell- then the cell will become more negative in charge = Repolarization (or Hyperpolarization).

-The STRONGER the stimulus = The greater the change in charge inside the cell (the more Na+ will enter = the greater the depolarization event) 5. Look at slide 53.What is an Action Potential?
-Where does it occur in a
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