psyc 3 ch 1-2
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
When the neuronal membrane is at rest, the sodium channels ____.
are closed, so there is almost no flow of sodium
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
A drug that blocks the sodium gates of a neuron's membrane will ____.
block the action potential
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 a neuron is at rest, what is primarily 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
What action tends to open the sodium gates across a neuron's membrane?
depolarization of the membrane
What occurs when a stimulus shifts the potential inside a neuron from the resting potential to a more negative potential?
hyperpolarization
Under which conditions would the sodium-potassium pump likely be far less effective in creating a concentration gradient?
if selective permeability of the membrane did not exist
The function of a myelin sheath is to ____.
increase the velocity of transmission along an axon
Which event will increase the concentration gradient of sodium?
increasing activity of the sodium-potassium pump
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
Electrical gradients lead to the ____.
movement of ions to areas having opposite electrical charges
Which of the following describes selective permeability?
only certain molecules are allowed to cross the membrane freely
Local anesthetic drugs attach to the sodium channels of the membrane, which
prevents sodium ions from entering and stopping action potential
At the peak of the action potential, the electrical gradient of potassium ____.
pushes potassium out of the cell
What term describes the difference in voltage that typically exists between the inside and the outside of a neuron?
resting potential
The action potential of a neuron depends mostly on what movement of ions?
sodium ions entering the cell
In the normal course of an action potential, ____.
sodium remains much more concentrated outside than inside the neuron
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
What is one major cause for the resting potential of a neuron's membrane?
the sodium-potassium pump
The neuron will produce an action potential only if the depolarization exceeds the ____.
threshold of excitation
What is the approximate resting potential of the inside of a neuron's membrane, relative to the outside?
-70 millivolts
The concentration gradient refers to the ____.
difference in distribution for various ions between the inside and outside of the membrane
The speed of an action potential down an unmyelinated axon is best described as ____.
faster in thick axons than in thin ones
Which action would depolarize a neuron?
increasing membrane permeability to sodium
The resting potential is mainly the result of ____.
negatively charged proteins inside the cell
The resting potential of a neuron refers to the ____.
net negative charge on the inside of a neuron
According to the all-or-none law, ____.
once an axon reaches threshold, the amplitude and velocity of an actin potential are nearly equal each time
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 leak channels ____.
permit potassium ions to pass slowly
The primary feature of a neuron that prevents the action potential from traveling back from where it just passed is the ____.
refractory period
What occurs when depolarization is less than the cell's threshold?
sodium crosses the membrane only slightly more than usual
The idea that a neuron's membrane is polarized refers to a difference in electrical potential between ____.
the inside and the outside of the membrane
After the peak of an action potential, what prevents sodium ions from continuing to enter the cell?
the sodium gates in the membrane close
