Copyright ©Mark Nelson, 2002. All rights reserved.
Chapter 5: The Nerve Impulse
What you need to know
(exam questions will be a drawn from this subset of material)
What's the difference between a nerve impulse and an action
potential ? (p. 109)
What do the terms depolarization and hyperpolarization mean?
What are typical values for the amplitude and duration of an action potential?
Why is an action potential said to be all-or-none? (p. 110, 115)
What is the key biophysical mechanism that underlies the generation of
an action potential? (p. 110)
Outline the sequence of conductance changes that takes place for
Na + and K+ channels during an AP? (p. 116)
Outline the sequence of ionic currents (Na+ and K+
) that flow during the different stages of the AP? (p. 116)
What role does positive feedback play in the generation of the AP?
What's the functional role of sodium inactivation? (p. 117)
Do potassium channels inactivate, just like sodium channels? (p. 117)
If you poison a neuron with a metabolic inhibitor that stops operation of
the Na-K pump, can the neuron still generate APs? (p. 117)
When Na+ ions rush into a neuron during an AP, is the intracellular
concentration of Na+ changed significantly? (p. 117-118)
What happens to the size of an AP if you increase the external Na+
concentration? (p. 118-119)
Who were Hodgkin and Huxley? (p. 119-122)
What is a voltage clamp? (p. 119-122)
Draw the clamp current that might be seen in a squid axon when the clamp
voltage is stepped from -60 mV to 0 mV. (p. 119)
What would the clamp current look like in the above experiment if
Na+ channels were blocked? if K+ channels were blocked?
What would the clamp current look like in the above experiment if the external
[Na+] were reduced to match the internal [Na+]?
Draw the time course of changes in Na+ and K+ conductance during an action
potential? (p. 122)
Is there a particular voltage where the ionic conductance changes sign?
Who are Neher and Sakmann? (p. 122)
What is a patch clamp? (p. 122-124)
Does an individual ionic channel show a continuous range of conductance
states? (p. 122-124)
What are the two main functional types of "gates" in voltage-gated ion channels?
What is the refractory period of a neuron? (p.
What is the difference between the absolute and the relative refractory
period? (p. 125).
What is the biophysical basis of the refractory period? (p. 125)
Are Na+ and K+ channels associated with the AP the
only kinds of voltage-gated channels that are found in neurons? (p. 126-128)
How does the AP propagate down an axon? (p. 129)
Why doesn't the AP propagate back in the direction from which it came?
What direction to APs usually propagate? (p. 130)
What would happen if you initiated an AP by stimulating the terminal arbor
of an axon? (p. 130)
What would happen if you initiated an AP in the middle of an axon, halfway
down its length? (not in text)
What would happen if you simultaneously initiated an AP at the soma and
at the terminal arbor of the same axon? (not
In an unmyelinated axon, do APs propagate faster in larger diameter or smaller
diameter axons? (p. 130)
What is a typical AP propagation velocity in unmyelinated axons ? (p. 130-131)
What does myelin do? (p. 130-131)
What are nodes of Ranvier ? (p. 131)
What is saltatory conduction ? (p. 131)
Why can APs propagate faster in myelinated axons? (p. 130-131)