A and P 11.2
Which of the following events will cause an EPSP?
Na ions enter postsynaptic cell
The Na+/K+ pump moves
Na+ out of and K+ into the cell
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.
Sometimes when you pull your dinner out of the microwave, you have to hold your fingertips to the food for a second or two before you can tell if it is hot or cold. Why does this happen?
The mechanoreceptors that have mechanically gated Na+ channels are allowed to open. The influx of Na+ ions causes a graded response, which takes time to reach the threshold at the axon hillock and lead to an action potential.
What do you think would happen to the neuronal action potential if the concentration of sodium ions in the extracellular fluid decreased significantly, to the point of reversing the gradient?
The neuron will stay in a depolarized state.
Tetrodotoxin is a toxin that blocks voltage-gated sodium ion channels. What effect would this have on the function of neurons?
The neuron would be unable to generate action potentials.
Predict the effect of the poison ouabain which blocks Na+/K+ pumps, on the neuronal action potential.
The potential would be above the resting state and can potentially lead to active depolarization.
Which of the following scenarios can increase the likelihood that a certain neuron will reach threshold and have an action potential?
There are equal amounts of EPSP's via spatial summation as there is temporal summation.
What membrane potential must generally be met in order to achieve threshold?
-55 mV
Saltatory conduction is slow due to the presence of insulating myelin around an axon.
False
The velocity of the action potential is fastest in which of the following axons?
a small myelinated axon
When is the generation of an action potential impossible, no matter the strength of the stimulus?
absolute refractory period
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
Voltage-gated sodium channels have both an activation gate and:
an inactivation gate.
A local hyperpolarization that makes the membrane potential of the postsynaptic neuron more negative is
an inhibitory postsynaptic potential (IPSP).
Which of the following moves the membrane potential of the postsynaptic neuron closer to threshold?
excitatory postsynaptic potential (EPSP)
What is NOT associated with a chemical synapse?
gap junction
When voltage-gated sodium ion channels are inactivated, the neuron is
in the absolute refractory period
If a drug inhibits the enzyme Acetylcholinesterase, the effect will be:
increased ACh availability in synaptic cleft
Determine the fiber type in which propagation of an action potential will occur most quickly.
myelinated type A fiber
Voltage-gated sodium channels are activated:
only if the cell is depolarized to threshold.
What would most likely lead to an inhibitory postsynaptic potential (IPSP)?
opening of potassium ion channels
During repolarization of a neuron:
potassium ions move out of the cell.
The type of action potential propagation in which action potentials are only generated at nodes of Ranvier is called __________.
saltatory conduction
Simultaneous stimulation from multiple presynaptic neurons will result in __________.
spatial summation
Summation that results from the cumulative effect of multiple synapses at multiple places on the neuron is
spatial summation.
The small space between the sending neuron and the receiving neuron is the
synaptic cleft.
If a resting axon increases its permeability to sodium ions:
the influx of sodium ions will increase and the membrane will depolarize.
If a drug inhibits neurotransmitter receptors on the postsynaptic cells:
the neurotransmitter will have no effect in the postsynaptic cell
The neuron that receives neurotransmitters from another neuron is called:
the postsynaptic neuron.
Conduction speed of a nerve impulse is influenced by the diameter of the axon and the presence or absence of a myelin sheath.
true
Electrical synapses are faster than chemical synapses due to the presence of gap junctions between cells.
true
Resting membrane potential is maintained by the sodium-potassium ion pump, or Na+/K+ ATPase, which brings:
two potassium ions into the cytosol and three sodium ions into the extracellular fluid.
Which type of fiber has the largest diameter?
type A
An action potential releases neurotransmitter from a neuron by opening which of the following channels?
voltage-gated Ca2+ channels
Repolarization begins as:
voltage-gated potassium ion channels activate.
Positive feedback loops are caused:
when a small physiological change leads to an amplified change in the same direction.
How is an action potential propagated along an axon?
An influx of sodium ions from the current action potential depolarizes the adjacent area.
Where are synaptic vesicles located in a neuron?
Axon terminals of the presynaptic neuron
Which of these ions triggers exocytosis of synaptic vesicles
Ca2+
Which of the following must happen first in the order events at a chemical synapse?
Calcium ion channels in the axon terminal open.
A new drug opens ligand-gated calcium ion channels in the membrane of the postsynaptic neuron. What effects would most likely occur?
It will depolarize the cell. If it reaches threshold AND if there are voltage-gated Na+ and K+ ion channels, there will be an induction of an action potential.
Why is the resting membrane potential negatively charged?
More potassium ions leak out of the neuron than move in.
The cells that form the regeneration tube during neural regeneration are called _
Schwann cells
Calcium ion entry into the axon terminal is necessary for the release of neurotransmitter into the synaptic cleft in a chemical synapse.
True
During depolarization, the membrane potential becomes more positive.
True
Which of the following is NOT one of the mechanisms for synaptic transmission termination?
Uptake of neurotransmitter into postsynaptic neuron
If a poison were to block voltage-gated calcium ion channels in the axon terminal, what effects would this have on the synaptic transmission?
Vesicles filled with neurotransmitters will not be able to fuse towards the membrane of the presynaptic
Which type of channels would you expect to find primarily at the axonal terminals?
Voltage-gated calcium ion channels
An EPSP will
bring the neuron closer to threshold
What ion triggers synaptic vesicles to release neurotransmitters into the synaptic cleft?
calcium
The majority of synapses in the nervous system are:
chemical
What type of synapse must have receptors to transmit signals?
chemical synapse
The presence of a synaptic cleft between cells is characteristic of:
chemical synapse.
Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.
chemically gated; postsynaptic
Action potential propagation in unmyelinated axons happens via:
continuous conduction
Which of the following is one of the mechanisms for termination of synaptic transmission?
degradation of neurotransmitter by enzyme
The influx of positive charges makes the membrane potential more positive and is known as:
depolarization
If a stimulus opens ligand-gated sodium ion channels, the neuron will
depolarize
Depolarization to threshold during action potential propagation in axons is due to:
diffusion of Na ions down to the next segment of the axon
Binding of the neurotransmitter to its receptor causes the membrane to __________.
either depolarize or hyperpolarize
Bidirectional, instantaneous synaptic transmission is typical of __________.
electrical synapses
The relative refractory period is caused by:
hyperpolarization
A series of measurements with a voltmeter show a neuron's membrane potential becoming more negative, from -70 mV to -85 mV. This neuron is experiencing a:
hyperpolarization phase.
Nicotine is addictive because it causes dopamine-releasing neurons to fire more action potentials. Nicotine will therefore cause:
increased levels of dopamine in the synaptic cleft
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.
Conduction speed will be fastest in a
large myelinated axonb
Which of the following is the primary factor in the maintenance of a cell's negative charge during resting membrane potential?
leak channels
Postsynaptic potentials are:
local potentials
Graded potentials:
may cause either depolarization or hyperpolarization.
What specific type of gated channel opens or closes in response to physical distortion of the membrane surface, such as vibrations or pressure?
mechanically-gated
A molecule that carries information across a synaptic cleft is a
neurotransmitter.
During the absolute refractory period:
no additional stimulus, no matter how strong, can produce an additional action potential.
Compared to chemical synapses, electrical synapses:
offer faster cell-cell communication
Which of the following would NOT terminate the effects of the neurotransmitter?
presence of calcium ions in the presynaptic neuron
In a synapse, neurotransmitters are stored in vesicles located in the
presynaptic neuron
If the receptor site for a neurotransmitter were completely blocked:
synaptic transmission would fail.
When a second excitatory postsynaptic potential (EPSP) arrives at a single synapse before the effects of the first have disappeared, what results?
temporal summation
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.
When calcium ions enter the synaptic terminal,
they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.
Which statement best describes the all-or-none principle?
An action potential happens completely, or it doesn't happen at all.
