Pearson neuron review Flashcards
Where do most action potentials originate?
Initial segment
What opens first in response to a threshold stimulus?
Voltage-gated Na+ channels
What characterizes depolarization, the first phase of the action potential?
The membrane potential changes from a negative value to a positive value.
What characterizes repolarization, the second phase of the action potential?
Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.
What event triggers the generation of an action potential?
The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.
What is the first change to occur in response to a threshold stimulus?
Voltage-gated Na+ channels change shape, and their activation gates open.
Place the events involved in the propagation of an action potential in the correct order of occurrence from 1 to 5.
- Local current flows to the axon segment
- Axon segment depolarized to threshold
- Voltage-gated Na+ channels open
- Influx of Na+
- AP regenerated in adjacent axon segment
Saltatory propagation occurs in _________ axons, in which action potentials _________.
Myelinated; move from one node of Ranvier to another
In a synapse, neurotransmitters are stored in vesicles located in the __________.
presynaptic neuron
An action potential releases neurotransmitter from a neuron by opening which of the following channels?
voltage-gated Ca2+ channels
Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.
chemically gated; postsynaptic
Binding of the neurotransmitter to its receptor causes the membrane to __________.
either depolarize or hyperpolarize
The mechanism by which the neurotransmitter is returned to a presynaptic neuron’s axon terminal is specific for each neurotransmitter. Which of the following neurotransmitters is broken down by an enzyme before being returned?
acetylcholine
What type of conduction takes place in unmyelinated axons?
Continuous conduction
An action potential is self-regenerating because __________.
depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment
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
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
What changes occur 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.
In which type of axon will velocity of action potential conduction be the fastest?
Myelinated axons with the largest diameter
The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____.
K+; Na+
During depolarization, which gradient(s) move(s) Na+ into the cell?
both the electrical and chemical gradients
What is the value for the resting membrane potential for most neurons?
–70 mV
The Na+–K+ pump actively transports both sodium and potassium ions 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.
The concentrations of which two ions are highest outside the cell.
Na+ and Cl–
A resting neuron is an unstimulated neuron that is not presently generating an action potential. The resting membrane potential is the separation of the relative positive and negative charges across the membrane of a cell at rest.
The concentration of ____
is higher outside than inside the cell.
Na+
The resting membrane potential is maintained by Na+-K+ pumps that actively transport____into and____ out of the cell
K+, Na+
The concentration of ____ is higher inside than outside the cell. Target 4 of 5
K+
The membrane is more permeable to
K+
How is an action potential propagated along an axon?
An influx of sodium ions from the current action potential depolarizes the adjacent area.
Why does the action potential only move away from the cell body?
The areas that have had the action potential are refractory to a new action potential.
The velocity of the action potential is fastest in which of the following axons?
a small myelinated axon
The generation of an action potential in a neuron requires the presence what type of membrane channels?
voltage-gated channels
Action potentials (nerve impulses) are changes in the membrane potential that, once started, will affect the entire excitable membrane. The first action potential is usually generated at the initial segment of the neuron’s axon. This activity will test your understanding of the sequence of events that occur at the membrane of the initial segment of the axon during generation of an action potential.
- Threshold stimulus Na+ channels open
- Na+ influx Depolarization
- Na+ channels close K+ channels open
- K+ efflux Repolarization
- Hyperpolarization K+ channels close
The concentrations of which two ions are highest outside the cell?
Na+ and Cl−
Let’s consider a scenario in which the resting membrane potential changes from −70 mV to +70 mV, but the concentrations of all ions in the intracellular and extracellular fluids are unchanged. Predict how this change in membrane potential affects the movement of Na+. The electrical gradient for Na+ would tend to move Na+ __________ while the chemical gradient for Na+
would tend to move Na+__________.
out; in
For each of the following, indicate whether the condition will cause the membrane potential to become more positive, more negative, or largely unchanged when compared to the normal physiological resting membrane potential.
More Positive
- Triple the number of Nat leak channels
- Double the concentration of K+
outside the cell
More Negative
- Decrease the concentration of Na+ outside the cell by half
- Double the number of K+ leak channels
Largely Unchanged
- Double the size of the cell without adding channels
- Double the number of closed channels for K+
: Although it plays a role, it is not a primary determinant of the resting membrane potential
Na+ Permeablity
: The primary determinant of the resting membrane potential
K+ permeability
: The point at which there is no net movement of K+ into or out of the cell
Membrane Potential of -90 mV
: The resting membrane potential of the cell target
Membran Potential of -70mV
The small space between the sending neuron and the receiving neuron is the
Synaptic cleft.
A molecule that carries information across a synaptic cleft is a
Neurotransmitter.
When calcium ions enter the synaptic terminal,
they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron
When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron,
ion channels in the plasma membrane of the receiving neuron open
If a signal from a sending neuron makes the receiving neuron more negative inside,
The receiving neuron is less likely to generate an action potential
