Tutorial - Week 3 Content

Question 1

Which of the following mechanisms is used by neurones to encode information?

a. the size of action potentials
b. the width of the action potentials
c. the number of action potentials per unit time
d. the number of action potentials per millivolt
e. the shape of action potentials

Answer 1

c. the number of action potentials per unit time (frequency coding)

Question 2

The loss of positive ions from the interior of a neurone at rest would do which of the following?

a. hypopolarise the neurone
b. hyperpolarise the neurone
c. cause saltatory conduction
d. cause an action potential
e. depolarise the neurone

Answer 2

b. hyperpolarise the neurone

Question 3

The hyperpolarising phase of the action potential is caused by which of the following?

a. slow-closing of voltage gated potassium channels
b. sodium channel activation
c. sodium channel inactivation
d. voltage-gated sodium ions opening
e. slow opening of voltage gated potassium channels

Answer 3

a. slow-closing of voltage gated potassium channels

Question 4

At the resting membrane potential the majority of ion channels that are open are which of the following?

a. sodium channels
b. ligand gated ion channels
c. chloride channels
d. potassium channels
e. at rest there are no ion channels open

Answer 4

d. potassium channels (membrane is highly permeable to K+)

Question 5

Which of the following is NOT a feature of graded potentials?

a. they can result in a decrease in the membrane potential
b. they only affect a restricted (local) region of the membrane
c. they can result in an increase in the membrane potential
d. they alter the excitability of neurones
e. their size is indirectly proportional to the size of the stimulus

Answer 5

e. their size is indirectly proportional to the size of the stimulus

It is actual directly proportional

Question 6

Explain the difference between voltage-gated and ligand-gated ion channels

Answer 6

Answer with marking scheme:

• Voltage-gated channels are ion channels where the state of the gate (1/2) is determined by the membrane potential (1/2)
• These channels have a molecular sensor that measures the membrane potential (1/2) and opens or closes the gate depending on it’s value.
• Ligand-gated ion channels are ion channels where the gate is opened by a binding of a chemical (1)
• The chemical (or neurotransmitter) binds to a receptor associated with the channel