Sodium ions are moving in, and the membrane potential is becoming less negative than the resting membrane potential.
question
Autonomic motor neurons are subdivided into the
answer
sympathetic and parasympathetic branches.
question
To increase the amount of neurotransmitter released onto a postsynaptic cell, the presynaptic cell would have to
answer
To increase the amount of neurotransmitter released onto a postsynaptic cell, the presynaptic cell would have to
send action potentials with higher frequency.
question
Part complete
Neurotransmitters are usually released into synapses by
answer
exocytosis
question
In response to binding a neurotransmitter, a postsynaptic cell can
answer
In response to binding a neurotransmitter, a postsynaptic cell can
open chemically gated ion channels, causing graded potentials known as fast synaptic potentials, close ion channels through G proteins and second messenger systems, producing slow responses, and regulate protein synthesis and affect the metabolic activities of the postsynaptic cell.
question
Where do most action potentials originate
answer
Initial segment
question
What opens first in response to a threshold stimulus
answer
Voltage-gated Na+ channels
question
What characterizes depolarization, the first phase of the action potential
answer
The membrane potential changes from a negative value to a positive value.
question
What characterizes repolarization, the second phase of the action potential?
answer
Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.
question
What event triggers the generation of an action potential?
answer
The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV
question
What is the first change to occur in response to a threshold stimulus
answer
Voltage-gated Na+ channels change shape, and their activation gates open.
question
Neurotransmitter is stored and released from
answer
axon terminals and axon varicosities.
question
When a second EPSP arrives at a single synapse before the effects of the first have disappeared, what occurs?
answer
temporal summation
question
Conduction speed can be increased by
answer
increasing the length of a neuron.
removing myelin.
increasing the diameter of a neuron
question
increasing the length of a neuron.
removing myelin.
increasing the diameter of a neuron
answer
Continuous conduction
question
An action potential is self-regenerating because
answer
depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment
question
Why does regeneration of the action potential occur in one direction, rather than in two directions
answer
The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential.
question
What is the function of the myelin sheath
answer
The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.
question
What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?
answer
Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.
question
In which type of axon will velocity of action potential conduction be the fastest?
answer
Myelinated axons with the largest diameter
question
Which type of receptor would bind acetylcholine and be found in skeletal muscle
answer
Nicotinic cholinergic
question
A damaged neuron has a better chance of survival and repair if the ________ is/are undamaged
answer
cell body
question
location of voltage-gated ion channels
answer
axon
question
Action potentials are mainly associated with the membranes of
answer
axons only
question
In order for a synapse to be an effective means of cellular communication, removal of neurotransmitter molecules from the synapse is important.
answer
false
question
When voltage-gated K+ channels of a resting neuron open,
answer
K+ leaves the neuron.
question
Repair of damaged neurons can be assisted by certain neurotrophic factors secreted by the
answer
Schwann cells only.
question
A chemical synapse ALWAYS includes which of the following?
The region where the axon terminal meets its target cell is called the
answer
synapse
question
When voltage-gated Na+ channels of a resting neuron open,
answer
Na+ enters the neuron and the neuron depolarizes.
question
Presynaptic facilitation makes a pathway
answer
more likely to be in use, just through depolarization of selected neurons and capable of alteration, just through training and conditioning.
question
activation gate
answer
opens during depolarization
question
Repolarization
answer
Potassium ions are moving out, and the membrane potential is becoming more negative as it moves back toward the resting membrane potential
question
Hyperpolarization
answer
Potassium ions are moving out, and the membrane potential is becoming more negative than the resting membrane potential.
question
During an action potential, when does sodium ion permeability begin to significantly decline?
answer
at the peak of depolarization
question
What is the definition of an ionotropic receptor?
answer
A receptor that alters ion flow when it binds with its ligand
question
Graded potentials can
answer
act as signals over short distances and make an action potential more or less likely.
question
The enteric nervous system is a network of neurons that function in controlling
answer
digestion
question
If a hyperpolarizing graded potential and a depolarizing graded potential of similar magnitudes arrive at the trigger zone at the same time, what is most likely to occur?
answer
Nothing. They will cancel each other out.
question
Learning and memory are thought to be due to synaptic changes known as
answer
long-term potentiation.
question
The following are the main steps in the generation of an action potential:
answer
1. sodium channels are closed
2. more voltage-regulated potassium channels open and potassium moves out of the cell, initiating repolarization
3. sodium channels return to their resting properties
4. a graded depolarization brings depolarization to threshold
5. a temporary hyperpolarization occurs
6. sodium channels open
7. sodium ions enter the cell and further depolarization occurs
4, 6, 7, 1, 2, 5, 3.
question
In general, the nervous system is made up of which two types of cells?
answer
neurons
glia
question
When multiple, possibly even conflicting signals reach a neuron, the neuron evaluates the signals and may respond or not. This property is called
answer
postsynaptic integration.
question
When more action potentials arrive at the axon terminal, how is a postsynaptic neuron affected?
answer
Neurotransmitter release increases, increasing the frequency or magnitude of graded potentials in the postsynaptic neuron.
question
The axon is connected to the cell body by the
answer
axon hillock.
question
receive(s) most of the incoming synapses
answer
dendrites
question
The multiple thin, branched structures on some neurons whose main function is to receive incoming signals are the
answer
dendrites
question
How is an action potential propagated along an axon?
answer
An influx of sodium ions from the current action potential depolarizes the adjacent area.
question
Why does the action potential only move away from the cell body?
answer
The areas that have had the action potential are refractory to a new action potential.
question
The velocity of the action potential is fastest in which of the following axons?
answer
a small myelinated axon
question
originate(s) at the trigger zone
answer
action potential
question
The small space between the sending neuron and the receiving neuron is the
answer
synaptic cleft.
question
A molecule that carries information across a synaptic cleft is a
answer
neurotransmitter.
question
When calcium ions enter the synaptic terminal,
answer
they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.
question
When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron,
answer
ion channels in the plasma membrane of the receiving neuron open.
question
If a signal from a sending neuron makes the receiving neuron more negative inside,
answer
the receiving neuron is less likely to generate an action potential.
question
Identify the FALSE statement.
The voltage-gated sodium and potassium channels begin to open during the depolarization.
Under normal conditions, all action potentials in a given cell are identical.
Ions diffuse at nodes of Ranvier.
The amplitude of the action potential depends on the amplitude of the graded potential that precedes it.
answer
The voltage-gated sodium and potassium channels begin to open during the depolarization.
question
A home satellite dish receives signals from a satellite in outer space, allowing your television to display TV shows. Which part of a neuron is similar to the satellite dish?
answer
dendrites
question
Interneurons are found
answer
in the CNS
question
Which of the following is a similarity between slow synaptic potentials and fast synaptic potentials?
answer
Both stimulate the opening or closing of ion channels.
question
The afferent and efferent neurons together form the
answer
peripheral nervous system.
question
originate(s) on dendrites and cell bodies
answer
graded potential
question
The following are steps involved in transmission at the cholinergic synapse:
1. Chemically gated ion channels on the postsynaptic membrane are opened.
2. Calcium ions enter the axon terminal.
3. An action potential depolarizes the axon terminal at the presynaptic membrane.
4. Acetylcholine is released from storage vesicles by exocytosis.
5. Acetylcholine binds to receptors on the postsynaptic membrane.
answer
3, 2, 4, 5, 1.
question
In most cells, the concentration of ions contributing to the membrane potential is __________ in the intracellular fluid compared with the extracellular fluid, with the exception of __________ ions.
answer
lower; potassium
question
The falling phase of the action potential is due mainly to
answer
K+ flow out of the cell only.
question
Once the action potential reaches the axon terminal, what happens next?
release of a neurohormone into the blood
exocytosis of a neurocrine
release of a neurotransmitter into the synaptic cleft
Any of the above could happen next.
answer
any of the above
question
Information coming into the central nervous system is transmitted along ________ neurons.
answer
afferent and sensory
question
The neurotransmitter thought to be involved in learning and memory is
answer
glutamate.
question
Which will best increase the conduction rate of action potentials?
answer
Increase the diameter of the axon, increase the resistance of the axon membrane to ion leakage.
question
When comparing action potentials to graded potentials, an/two important distinguishing characteristic/s is/are
answer
graded potentials can undergo summation and the rate of action potentials is limited by the refractory period.
question
Conduction occurs along an axon because
answer
entry of Na+ stimulates the adjacent channels to open.
question
Which ion(s) is/are higher in concentration inside the cell compared to outside?
answer
potassium
question
The Nernst equation can be used to predict
answer
the membrane potential resulting from permeability to a single ion.
question
size increases if stimulus strength increases
answer
graded potential
question
The brain and spinal cord together compose the
answer
central nervous system
question
Inhibitory postsynaptic potentials (IPSPs)
answer
result in hyperpolarizations.
question
The term axonal transport refers to
answer
vesicle transport of proteins and organelles down the axon.
question
Arrange the following events in the proper sequence:
1. Efferent neuron graded potential reaches threshold and fires an action potential.
2. Afferent neuron graded potential reaches threshold and fires an action potential.
3. Target organ responds.
4. CNS reaches decision about response.
5. Sensory receptor detects change in the environment.
answer
5, 2, 4, 1, 3
question
The basis of integration of neural information is
answer
addition of postsynaptic potentials overlapping in time and space.
question
Identify the FALSE statement.
IPSPs depolarize the membrane.
The trigger zone is the integrating center of the neuron.
EPSPs that reach threshold can initiate an action potential.
All of the statements are true.
answer
IPSPs depolarize the membrane.
question
can involve ion channels regulated by chemicals
answer
graded potential
question
Clusters of nerve cell bodies in the peripheral nervous system are called
answer
ganglia.
question
The total amount of neurotransmitter released at the axon terminal is directly related to the
answer
total number of action potentials.
question
The changing of activity at synapses, which occurs throughout life, is termed
answer
synaptic plasticity.
question
In the membrane of a resting nerve cell, when chemically gated Cl- channels open,
answer
Cl- ions enter the cell.
question
An excitatory postsynaptic potential (EPSP)
answer
depolarizes a neuron, increasing the likelihood of an action potential.
question
Voltage-gated channels are located
answer
in the membranes of dendrites, in the membranes of axons, and on the neuron cell body.
question
Which does NOT influence the time necessary for a nerve impulse to be conducted by a neuron?
answer
whether axon is sensory or motor
question
Excitatory neurotransmitters of the CNS usually act by opening ________ channels.
answer
Na+
question
Inhibition of neural activity can result from
answer
presynaptic events and postsynaptic events.
question
When sodium channels open during an action potential, the opening is caused by
answer
presence of positive charge.
question
where most graded potentials originate
answer
dendrites
question
Neurotransmitters are released from the
answer
axon terminals.
question
Which of the following would have the fastest action potentials?
answer
A myelinated axon with a large diameter
question
Whether a neuron fires an action potential depends on __________.
answer
a graded potential above threshold voltage reaching the trigger zone
question
Once a stimulus binds a receptor on the cell's membrane, what could happen next?
answer
Any of these actions could happen next.
question
The ion necessary to initiate the release of acetylcholine into the synaptic cleft is
answer
calcium.
question
Which type of synapse is most common in the nervous system?
answer
chemical
question
The rising phase of the action potential is due to
q
answer
Na+ flow into the cell only.
question
The tip of an embryonic nerve cell's axon is called a
answer
growth cone.
question
The sympathetic and parasympathetic nervous systems are divisions of which system?
answer
The autonomic nervous system
question
The primary problem in hyperkalemia is that
answer
neurons are easier to excite because their resting potential is closer to threshold and neurons respond too quickly to smaller graded potentials.
question
The all-or-none principle states that
answer
all stimuli great enough to bring the membrane to threshold will produce action potentials of identical magnitude.
question
The portions of a neuron that extend off of the roughly spherical cell body are usually collectively called
answer
processes.
question
Which neural term is a synonym for action potential?
answer
Nerve impulse
question
The sodium-potassium exchange pump
answer
requires ATP to function.
question
The absolute refractory period of an action potential
answer
ensures one-way travel down an axon, allows a neuron to ignore a second signal sent that closely follows the first, and prevents summation of action potentials.
question
Exocrine glands, smooth muscles, and cardiac muscles are controlled by the
answer
autonomic motor division
question
Anterograde and retrograde axonal transport are forms of ________ transport.
answer
fast
question
When two or more graded potentials arrive at the trigger zone, which of the following could happen?
answer
An excitatory and inhibitory signal can cancel each other out; two excitatory stimuli may be additive, and summation could occur; and two inhibitory stimuli may be additive, resulting in lower excitability.
question
The collection of axons that carries information between the central nervous system and the peripheral effectors is called the
answer
nerve
question
Which is NOT a known drug effect on synaptic function?
answer
change the type of neurotransmitter found in the synaptic vesicle
question
result(s) from influx of sodium
answer
C. Both (graded and action potentials)
question
Which is a similarity between spatial summation and temporal summation?
answer
Both allow subthreshold graded potentials to trigger an action potential.
question
If the resting axon's membrane becomes more permeable to potassium ions,
answer
it will take a stimulus of larger magnitude to initiate an action potential.
question
The resting membrane potential results from
answer
uneven distribution of ions across the cell membrane and differences in membrane permeability to ions.
question
Graded potentials may
Graded potentials may
depolarize the membrane to the threshold voltage.
hyperpolarize the membrane.
be called EPSPs or IPSPs.
initiate an action potential.
All of the statements are true.
answer
all of the statements are true
question
Some neurotoxins work essentially the same way as some local anesthetics, which is to
answer
bind to Na+ channels and prevent depolarization by blocking Na+ entry into the cell.
question
Which is the most common location where action potentials start in efferent neurons?
answer
axon hillock
question
The pattern of synaptic connectivity where a large number of presynaptic neurons provide input to a single postsynaptic neuron, is known as
answer
convergence.
question
A ligand binds to a receptor-channel that stimulates a channel to open. This is a chloride channel. This will stimulate __________.
answer
an inhibitory postsynaptic potential (IPSP)
question
How would the absolute refractory period be affected if voltage-gated sodium channels remained inactivated?
answer
It would be longer than normal.
question
In a synapse, neurotransmitters are stored in vesicles located in the __________.
answer
presynaptic neuron
question
An action potential releases neurotransmitter from a neuron by opening which of the following channels?
answer
voltage-gated Ca2+ channels
question
Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.
answer
chemically gated; postsynaptic
question
Binding of the neurotransmitter to its receptor causes the membrane to __________.
answer
either depolarize or hyperpolarize
question
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?
answer
acetylcholine
question
A stronger stimulus to a neuron results in __________.
answer
stronger graded potentials
question
Calcium is important in the synapse because it
answer
signals the exocytosis of the neurotransmitter.
question
Spatial summation refers to
answer
multiple graded potentials arriving at one location.
question
Where in the neuron is an action potential initially generated?
answer
axon hillock
question
The depolarization phase of an action potential results from the opening of which channels?
answer
voltage-gated Na+ channels
question
The repolarization phase of an action potential results from __________.
answer
the opening of voltage-gated K+ channels
question
Hyperpolarization results from __________.
answer
slow closing of voltage-gated K+ channels
question
What is the magnitude (amplitude) of an action potential?
answer
100 mV
question
may be covered with myelin
answer
axon
question
Which statement is true when a neuron is at rest?
answer
The activation gate is closed and the inactivation gate is open.
question
In order to signal a stronger stimulus, action potentials become
answer
more frequent only.
question
When more action potentials arrive at the axon terminal, how are neurotransmitters affected?
answer
More molecules are released into the synapse.
question
What stops the rising phase of the action potential?
answer
The Na+ inactivation gate closes.
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