Chapter 4: The action potential

How long does an action potential last from the beginning of the rising phase to the end of the falling phase? Choose the correct option.

2 msec

Saxitoxin is a channel-blocking toxin produced by the dinoflagellates of the genus Gonyaulax.

True

A voltage clamp is:-

A device that enables the "clamping" of a membrane potential of an axon at any value chosen

What is meant by the action potential threshold? Choose the correct option.

Critical level of depolarization required to trigger an action potential

What property of the voltage-gated potassium channels allows K+ ions to pass? Choose the correct option.

Depolarization causes the four polypeptide subunits specific to the voltage-gated K+ channel to twist into a shape that allows K+ ions to pass.

In myelinated axons, action potentials are conducted slowly. This type of action potential propagation is called saltatory conduction. True or false?

False

Neurons vary in shape, size, gene expression, and connections, but all have identical electrical properties. True or false?

False

The movement of what ion occurs in the rising phase of the action potential? Choose the correct option.

Inward Na+

How does myelin help increase conduction velocity? Choose the correct option.

It provides electrical insulation.

Optogenetic techniques have been developed allowing researchers to do which of the following by introducing foreign genes into test animals? Choose the correct option.

Open ion channels in response to blue light

How does tetrodotoxin (TTX) affect channels? Choose the correct option.

TTX blocks Na+ channels.

Where is the spike-initiation zone in a typical neuron? Choose the correct option.

The axon hillock

Why do action potentials travel in only one direction? Choose the correct option.

The membrane just behind the action potential is refractory due to inactivated sodium channels.

How does the sodium channel selectivity filter differentiate between Na+ and K+ ions? Choose the correct option.

The sodium channel admits a Na+ water complex, with the water serving as a molecular chaperone through the channel.

What is the absolute refractory period? Choose the correct option.

The time period of about 1 msec after an action potential before another one can be initiated

How have toxins been used as a research tool? Choose the correct option.

To study the consequences of blocking action potentials

The firing frequency of action potentials reflects the magnitude of the depolarizing current. True or false?

True

The size of the giant axon of the squid illustrates that neural pathways that are important for survival have unusually large axons. True or false?

True

The spike-initiation zone in most peripheral sensory neurons occurs near the sensory nerve ending. True or false?

True

How long does it take for a voltage-gated potassium channel to open? Choose the correct option.

Voltage-gated potassium channels open about 1 msec after the membrane is depolarized.

What role do voltage-gated potassium channels play in the action potential? Choose the correct option.

Voltage-gated potassium channels restore negative membrane potential after the spike.

After-hyperpolarization there is a:-

gradual restoration of the resting potential

In saltatory conduction the action potentials...

jump from node to node

The correct order of an action potential is:-

rising phase, overshoot, falling phase, undershoot

This is where a protein forms a pore in the membrane that is highly selective to Na+, and the pore is opened and closed by changes in the membrane potential

voltage-gated sodium channel