1
Chapter 6: Nervous Systems
Revised 20 September 2011 for 12th Edition
Section B3
Which ion moving in which direction (in or out of the cell) is responsible for hyperpolarization?
How do graded potentials differ from action potentials in terms of location, extend of spread, and
amplitude?
What are synonyms of “graded potential?”
What is the difference between “depolarizing” and “hyperpolarizing?”
For a graded potential, how does the voltage (potential) across the membrane change as one moves
further from the site of a depolarization?
Why are graded potentials described as “decremental?”
Why are graded potentials unsuitable for signaling over distances greater than 1-2 mm?
In addition to leak channels (which are always open), what are the various categories of gated ion
channels?
What distinguishes an action potential from a graded potential? (There are many differences.)
What types of cells can produce action potentials?
(T) Do dendrites of most neurons produce action potentials? Why or why not?
What is the typical duration of an action potential? (hint: look at the X axis of Fig. 6-19.)
What causes the depolarizing phase of an action potential?
Why doesn’t the membrane potential reach E Na+ during an action potential?
What two events are responsible for the repolarizing phase of an action potential?
Which ions are moving in which direction through the membrane during an afterhyperpolarization?
Is an action potential associated with measurable changes in the concentrations of ions in a cell?
2
What is responsible for maintenance the ion gradients across the cell membrane, even during periods of
rapidly repeating action potentials?
Explain how the rising phase of an action potential involves positive feedback.
What types of ion channels must be present in cells or regions of cells that produce action potentials?
During an action potential, which types of ion channels open first and which type opens after a slight
delay? Which type closes spontaneously?
What are the main differences between voltage gated Na+ and K+ channels?
If a depolarization does not reach threshold, is a positive feedback cycle involving Na+ activated?
Why are subthreshold potentials considered graded potentials?
What is an action potential described as “all-or-none?”
How do local anesthetics such as lidocaine work?
What is tetrodotoxin and how has it been useful to neuroscientists?
If all action potential are the same “size” then how can action potentials code the intensity of stimulus,
such as the loudness of a sound or the temperature of the skin?
What property of the Na+ voltage-gated ion channels accounts for the absolute refractory period?
What is the relative refractory period?
Explain how the properties of the voltage-gated Na+ channels are responsible for the absolute refractory
period and relative refractory period.
How is it that an action potential generated in the membrane of the initial segment of an action has the
same amplitude when it arrives in the axon terminal?
What prevents an action potential from “turning around” and being conducted backward through the
membrane it has just passed through?
What two factors determine the conduction velocity of an action potential in an axon?
Which types of axons have saltatory conduction?
Why is AP conduction in myelinated axons conduction faster than in non-myelinated axons?
3
Why are myelinated axons more energy efficient?
How is the disease multiple sclerosis related to myelin?
What causes potentials to occur naturally in sensory (afferent) neurons?
Some cells do not have a stable resting membrane potential. They spontaneously depolarize to reach
threshold. What term is given these cells?