Stanfield Chp. 7 Physiology
What type of conduction takes place in unmyelinated axons?
Continuous conduction
The membrane of neurons at rest are very permeable to _____ but only slightly permeable to _______.
K+ ; Na+
The concentrations of which two ions are highest outside the cell?
Na+ and Cl-
The Na+/K+ pump actively transports both sodium and potassium ion across the membrane to compensate for their constant leakage. In which direction is each ion pumped?
Na+ is pumped out of the cell and K+ is pumped into the cell
What prevents the Na+ and K+ gradients from dissipating?
Na+/K+ ATPase
The _______ maintains the resting membrane potential.
Na+/K+ pump
Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?
Resting membrane potential (RMP)
Which of the following correctly completes the sentence? The period of time after an action potential when another action potential cannot be generated is the _______.
absolute refractory period
Why doe the distribution of sodium and potassium ions across the plasma membrane of neurons not change appreciably, even following hundreds of action potentials?
The movement of sodium and potassium ions that occurs during an action potential is countered by the active transport of these ion by the Na+/K+ pump
The plasma membrane is much more permeable to K+ than to Na+. Why?
There are many more K+ leak channels than Na+ leak channels in the plasma membrane.
On what portion of the neuron do action potentials propagate?
axon
If the potential remains above threshold once it reaches the __________, the action potential will be generated.
axon hillock
In a neuron, where is the greatest concentration of voltage-gated sodium and voltage-gated potassium channels?
axon hillock
An action potential originates at the _______ and travels along the axon until it reaches the __________.
axon hillock : axon terminal
In a neuron, where are voltage-gated calcium channels located?
axon terminal
Where in the neuron are the nucleus and most of the organelles contained?
cell body (soma)
A change in a cell's membrane potential, such that the inside of the cell becomes more positive, is referred to as a ________ whereas if it becomes more negative it is referred to as __________.
depolarization : hyperpolarization
An action potential is self-generating because _________.
depolarizing currents established by the infux of Na+ flow down the axon and trigger an action potential at the next segment
Which of the following axons would have the fastest conduction velocity?
diameter = 20 microns, myelinated
How can action potentials relay information about the intensity of a stimulus, such as distinguishing between a loud and soft sound?
due to the frequency of action potentials
Which of the following potential dissipate in size as the potential moves away from the site of initiation?
graded potentials
What changes occurs to voltage-gated Na+ and K+ channels at the peak of depolarization ?
inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.
The opening of sodium channels causes a rapid _____ of sodium that ______ the neurons membrane.
influx : depolarizes
Sodium and potassium ions can diffuse across the plasma membranes of all cell because of the presence of what type of channel?
leak channels
What type of ion channels in the membrane of neurons allows ions to move across the membrane at rest and thereby contribute to resting membrane potential?
leak channels
Which of the following ion channels located in the plasma membrane of the neuron are always open and are largely responsible for the resting membrane potential?
leak channels
What type of ion channels in the membrane of neurons open or close in response to a neurotransmitter binding to its receptor?
ligand-gated channel
In which type of axon will velocity of action potential conduction be the fastest?
myelinated axons with the largest diamter
The depolarization phase of the action potential is generated by a rapid
opening of sodium channels
The depolarization of the membrane due to stimulus is a regenerative membrane meaning that, once sodium gates begin to open, even more sodium gates will be activated leading to a larger inflow of sodium ions and more depolarization until it is terminated when sodium gates close. This is an example of
positive feedback
At rest, the plasma membrane is more permeable to which of the following ions?
potassium (k+)
At resting membrane potential , the membrane is most permeable to __________, which moves _________ the cell due to its electrochemical gradient.
potassium : out of
Increased permeability to what ion is responsible for the relative refractory period?
potassium K+
Which of the following best describes the function of the myelin sheath?
reduce a membrane's ion permeability (reduces leakage of ions across the cell membrane).
The _________refractory period of an action potential is primarily due to _______ permeability of the plasma membrane to K+.
relative : increase
During the rapid depolarization phase of an action potential, the plasma membrane is more permeable to which of the following ions?
sodium Na+
What limits the maximum number of action potentials on an axon?
the absolute refractory period
A subthreshold stimulus will not generate an action potential whereas a suprathreshold stimulus does generate an action potential. This is an example of
the all-of-none principle
Why does regeneration of the action potential occur in one direction, rather than in two directions?
the inactivation gates of voltage=gated Na+ channels close in the node, or segment, that has just fired an action potential.
On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?
the inside surface of the plasma membrane is much more negatively charged that the outside surface.
What is the function of the myelin sheath?
the myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.
Which statement best describes the events responsible for the phase represented by the letter B in the figure?
the opening of the potassium channels
Which statement best describes the events responsible for the phase represented by the letter A in the figure?
the opening of the sodium channels
the resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.
the presence of concentration gradients and leak channels
As an action potential is propagated away from the axon hillock, why does propagation continue in one direction?
the region just behind the action potential is in the absolute refractory period.
Which of the following is true for graded potentials?
they can either be inhibitory or excitatory
What is the level of membrane depolarization required to induce the sodium channels positive feedback loop called?
threshold
What is the approximate resting membrane potential of neurons?
-70 mV
What is the resting membrane potential for most neurons?
-70 mV
During depolarization, which gradient(s) move(s) Na+ into the cell?
both the electrical and chemical gradients
