Chapter 4.2

Question 1

What are potassium leak channels

Answer 1

• they facilitate the outward movement of potassium
• as potassium continually leaks out of the cell
• > the cell loses a small amount of positive charge
• note as more potassium leaves the cell, the cell becomes more negative
• > so then potassium is pulled back in, as there is an attraction between the negatively charged cell and the positively charged potassium cation

Question 2

What is the equilibrium potential of potassium? What does this indicate

Answer 2

• it is -90 mV

- >therefore, a potassium ion is leaving the cell

Question 3

What is the equilibrium potential of sodium? What does this indicate?

Answer 3

• it is around 60 mV

- >therefore, sodium ions are entering the cell

Question 4

Why is the resting membrane potential closer to the potential of potassium?

Answer 4

-because the membrane is more permeable to potassium

Question 5

Does the Na/K ATPase contribute to the resting membrane potential

Answer 5

• yes
• > it continually pumps sodium and potassium back to where it started
• > doesn’t let the leak channels go against the gradient

-therefore, it does maintain the resting membrane potential

Question 6

Describe the two types of summation

Answer 6

1) Spatial summation
- >additive effects are based on a different number of neurons firing
- >and location of these signals

2) Temporal summation
- >multiple signals from one neuron are integrated during a relatively short period of time

Question 7

When are sodium channels inactivated

Answer 7

-when the membrane potential approaches +35 mV

Question 8

What are the three states of the sodium channels

Answer 8

1) closed
- >before the cell reaches threshold and after inactivation has been reversed

2) Open
- >from threshold to approximately +35 mV

3) Inactive
- >from approximately +35 mV to the resting potential

Question 9

What happens to voltage gated potassium channels once sodium channels are inactivated?

Answer 9

-voltage gated potassium channels open once sodium channels are inactivated

Question 10

What factors of an axon affect the speed at which action potentials are propogated?

Answer 10

1) Length of axon
- >increased length of the axon results in higher resistance
- >slower conduction

2) Cross sectional area of the axon
- >greater cross-sectional area allows for faster propogation due to decreased resistance

-note the effect of cross sections is more profound than that of axon length

Question 11

What does the increased intensity of a stimulus do to the action potential

Answer 11

-increased intensity= increased frequency of firing

Question 12

What is the difference between a ligand gated ion channel being activated on the post synaptic membrane and a G protein coupled receptor being activated

Answer 12

ligand gated ion channel
->post synaptic cell will be either depolarized or hyperpolarized

G protein-coupled receptor
->it will cause a change in the levels of cyclic AMP

Question 13

What are the two types of refractory periods

Answer 13

1) Absolute refractory periods
- >no amount of stimulation can cause another action potential to occur

2) Relative refractory period
- >there must be greater than normal stimulation to cause an action potential because the membrane is starting from a potential that is more negative than resting value

Question 14

How does saltatory conduction result

Answer 14

• through insulation

- >the signal hops from node to node

Question 15

How are neurotransmitter levels regulated

Answer 15

1) Broken down by enzymatic reactions
- >eg; the breakdown of acetylcholine by acetylcholinesterase

2) Reuptake carriers
- >eg; reuptake of serotonin, dopamine and noepinepherine

3) Diffusion out of the synaptic cleft
- >nitric oxide