Chapter 5
When a neuron's membrane is at rest, the concentration gradient tends to move sodium ____ the cell and the electrical gradient tends to move it ____ the cell.
into, into
A local neuron:
is a small neuron with no axon or a very short one.
Which of the following is NOT governed by the all-or-none law?
local neurons
The presence of an all-or-none law suggests that neurons can only convey different messages by changing their:
rate or pattern of action potentials.
The concentration gradient refers to:
the difference in distribution for various ions between the inside and outside of the membrane
What will NOT affect the speed of an action potential?
the length of the axon
Which two factors will affect the speed of an action potential?
the presence of myelin and the diameter of the axon
When the neuron is at rest, what is responsible for moving sodium ions out of the cell?
the sodium-potassium pump
The membrane of a neuron is specialized to:
control the exchange of chemicals between the inside and outside of the cell.
How is the speed of an action potential down an unmyelinated axon BEST described?
faster in thick axons than in thin ones
The membrane of a neuron is composed of ____ with ____ embedded in them.
fat molecules; proteins
Scorpion venom attacks the nervous system by:
opening sodium channels and closing potassium channels
A drug that decreases the flow of potassium through the potassium gates of the membrane would:
slow the return of the membrane to its resting potential.
The resting potential of the inside of a neuron's membrane is approximately?
-70 millivolts
If depolarization is less than the cell's threshold:
sodium crosses the membrane only slightly more than usual.
Which of the following describes selective permeability?
Only certain molecules are allowed to cross the membrane freely.
Just after the peak of the action potential, what movement of ions restores the membrane to approximately the resting potential?
Potassium ions leave the cell.
If you were to stub your toe and feel the pressure a second or two before you feel the pain, then which of the following statements is most likely true?
Pressure sensitive neurons are large and myelinated.
Which of the following is NOT true for sodium ions when the cell is at resting potential?
Sodium tends to be driven out of the neuron by the electrical gradient.
Which of the following is an advantage of having a resting potential?
The cell is prepared to respond quickly to a stimulus
Which of the following describes the transmission of information in a local neuron?
The signal decreases in strength as it travels.
Which of the following represents the all-or-none law?
The size of the action potential is independent of the strength of the stimulus that initiated it.
Which of the following is TRUE of local neurons?
They have short dendrites and axons
When the neuron is at rest, what is responsible for moving potassium ions OUT of the cell?
a concentration gradient
What causes potassium ions to leave the axon just after the peak of the action potential?
a continuing concentration gradient and the opening of the potassium gates
The all-or-none law states that:
a neuron produces an action potential of maximal strength, or none at all
During the entire course of events from the start of an action potential until the membrane returns to its resting potential, what is the net movement of ions?
sodium in, potassium out
In the normal course of an action potential:
sodium remains much more concentrated outside than inside the neuron.
The sodium-potassium pump, repeatedly transports three ____ ions out of the cell while drawing two ____ ions into it.
sodium; potassium
Negatively charged ions like ____ are mostly located outside the cell.
Chloride
Suppose we applied a drug to a neuron that caused its sodium gates to suddenly open wide. What would happen?
an action potential
What is one major cause for the resting potential of a neuron's membrane?
the sodium-potassium pump
A membrane produces an action potential whenever the potential across it reaches what level?
the threshold of excitation
To what does saltatory conduction refer?
the transmission of an impulse along a myelinated axon
The sodium-potassium pump, repeatedly transports ____ sodium ions out of the cell while drawing ____ potassium ions into it.
three; two
The primary feature of a neuron that prevents the action potential from traveling back from where it just passed is the:
absolute refractory period.
The presence of myelin and the diameter of the axon:
affect the speed of an action potential
Which of the following would produce a hyperpolarization of a neuron?
applying a negative charge inside the neuron with a microelectrode
When the neuronal membrane is at rest, the sodium channels:
are closed.
Where do most action potentials begin?
at the axon hillock
In a myelinated axon, where are sodium gates abundant?
at the nodes of Ranvier
At what point do the sodium gates begin to close, shutting out further entry of sodium into the cell?
at the peak of the action potential
Ordinarily, stimulation of a neuron takes place:
at the synapse.
The all-or-none law applies to:
axons
A drug that blocks the sodium gates of a neuron's membrane would:
block the action potential.
Local anesthetic drugs, such as Novocain, work by:
blocking the sodium gates.
A drug would prevent an action potential if it:
blocks the movement of sodium across the membrane.
When a membrane is at rest, what attracts sodium ions to the inside of the cell?
both an electrical gradient and a concentration gradient
When the neuron is at rest, what is responsible for moving potassium ions into the cell?
both the sodium-potassium pump and electrical gradient
The net effect of each cycle of the sodium-potassium pump is to:
decrease the number of positively charged ions within the cell.
Multiple sclerosis is one of several:
demyelinating diseases
What is the result if a stimulus shifts the potential inside a neuron from the resting potential to a potential slightly closer to zero?
depolarization
What tends to open the sodium gates across a neuron's membrane?
depolarization of the membrane
At what point do the sodium gates start to allow sodium into the neuron?
in response to any depolarization
What is the approximate resting potential of the inside of a neuron's membrane, relative to the outside?
-70 millivolts
What happens once an action potential starts?
It is regenerated at other points along the axon
In what way is a myelinated axon that has lost its myelin (through disease) different from an axon that was never myelinated?
It lacks sodium gates along parts of its surface
How does saltatory conduction affect energy use in a neuron?
It reduces the work load for the sodium-potassium pump.
What is meant by the term "concentration gradient" with respect to neurons?
Sodium and potassium ions are more concentrated on opposite sides of the membrane.
What happens to the ion gates when the membrane of a neuron starts to be depolarized?
Sodium gates open.
Stimulus A depolarizes a neuron just barely above the threshold. Stimulus B depolarizes a neuron to 10 mV beyond threshold. What can we expect to happen?
Stimulus A and stimulus B will produce the same response in the neurons.
After the peak of an action potential, what prevents sodium ions from continuing to enter the cell?
The sodium gates in the membrane close.
Why are local neurons more difficult to study?
They are so small.
When a membrane is at rest, what attracts potassium ions to the inside of the cell?
an electrical gradient
In what direction does a local neuron transmit information?
equally well in any direction
What are the nodes of Ranvier?
gaps in the myelin sheath
What is the result if a stimulus shifts the potential inside a neuron from the resting potential to a more negative potential?
hyperpolarization
Under what conditions is it impossible for a stimulus to produce an action potential?
if the membrane is in its absolute refractory period
Under which conditions would the sodium-potassium pump be far less effective in creating a concentration gradient?
if the plasma membrane were generally permeable
The function of a myelin sheath is to:
increase the velocity of transmission along an axon.
Which of the following events would increase the concentration gradient of sodium?
increased activity of the sodium potassium pump
Hyperpolarization is:
increased polarization.
Saltatory conduction ____ the velocity of action potentials, and ____ the amount of energy used by the neuron.
increases; decreases
Which of the following actions would depolarize a neuron?
increasing membrane permeability to sodium
What disease is related to the destruction of myelin sheaths?
multiple sclerosis
The myelin sheath is interrupted periodically by short sections of axon called?
nodes of Ranvier
According to the all-or-none law:
once an axon reaches threshold, the amplitude and velocity of an action potential are nearly equal each time.
If there is a depolarizing effect on a neuron, the result will be that the neuron will fire:
only if it reaches threshold.
When the potential across a membrane reaches threshold, the sodium channels:
open to let sodium enter the cell rapidly.
When a neuron's membrane is at rest, the concentration gradient tends to move potassium ____ the cell and the electrical gradient tends to move it ____ the cell.
out of, into
Voltage-activated channels are channels for which a change in the voltage across the membrane alters their:
permeability.
When the neuronal membrane is at rest, the potassium channels:
permit potassium ions to pass slowly.
When a neuron's membrane is at rest, which of the following molecules crosses through it MOST slowly?
potassium
The concentration gradient for potassium tends to:
push potassium out of the cell.
At the peak of the action potential, the electrical gradient:
pushes potassium out of the cell.
What is the difference in voltage called that typically exists between the inside and the outside of a neuron?
resting potential
Allowing only certain people to cross the street, and only at certain times. is comparable to a neuron's ____ with respect to ions.
selective permeability
The action potential of a neuron depends mostly on what movement of ions?
sodium ions entering the cell
A neuron's sodium gates are firmly closed and the membrane cannot produce an action potential during:
the absolute refractory period
Which feature of a neuron limits the number of action potentials it can produce per second?
the absolute refractory period
The selectivity of a neuron membrane is analogous to?
the blood-brain barrier
When you state that the neuron's membrane is polarized, you are referring to a difference in electrical potential between:
the inside and the outside of the membrane.
Electrical gradients lead to what kind of movements?
the movement of ions to areas having the opposite electrical charges
Concentration gradients lead to what kind of movements?
the movement of ions to areas of their lowest concentrations
The resting potential of a neuron refers to:
the net negative charge on the inside of the neuron
What will affect the speed of an action potential?
the resistance of the membrane
During the relative refractory period:
the sodium gates are reverting to their usual state.
The neuron will produce an action potential only if the depolarization exceeds what level?
the threshold of excitation
