Which of the following is not a function of astrocytes?
provide the defense for the CNS
Which of the following is expected to occur first if the membrane potential increase shown in the graph were to reach the threshold value indicated at -55 mV?
opening of voltage gated Na+ channels
Which of the following is not true of graded potentials?
They increase amplitude as they move away from the stimulus point.
Which of the following is NOT true of an electrical synapse?
They are specialized for release and reception of chemical neurotransmitters.
The sodium-potassium pump ejects two Na+ from the cell and then transports three K+ back into the cell in order to maintain the concentration gradients for sodium and potassium.
The sodium-potassium pump ejects three Na from the cell and then transports two K back into the cell in order to stabilize the resting membrane potential
Which of the following describes the excitatory postsynaptic potential?
short distance depolarization
Which statement best characterizes a K+ leak channel?
Trans-membrane protein channels that are always open to allow K+ to cross the membrane without the additional input of energy.
Assume you have a membrane with only potassium leak channels. The RMP is -90mV. Predict the RMP if we add Na+ leak channels.
The most likely RMP value of Na+ is __________.
Imagine that the cell membrane from the previous problem becomes more permeable to Na+. Predict how this will affect the RMP.
The RMP will be more positive.
Complete the following sentence. The operation of the Na+?K+ ATPase pump __________.
moves 3 Na+ to the ECF and 2 K+ to the cytoplasm
You are going to record RMP from a cell using an electrode. You place your electrode and record a resting membrane potential every millisecond. You record an initial value of -70mV; however, over time you notice that your recordings become more and more p
The cell's Na+?K+ ATPase pumps have stopped functioning.
Cl? is a common negatively charged extracellular ion. Predict the effect on the RMP if many Cl? gated channels are suddenly opened.
A more negative RMP would result.
Bipolar neurons are commonly ________.
found in the retina of the eye
Which of the following neurotransmitters inhibits pain and is mimicked by morphine, heroin, and methadone?
Which areas of this neuron would be classified as receptive regions?
Both A and B
Arrange these parts in order, from left to right, of a successful direct depolarization path within one neuron.
dendrite, cell body, axon hillock, axon, presynaptic terminal
Which of the following best characterizes depolarization?
small consecutive steps of Na+ penetration into the axon along its length
When an action potential arrives at the end of the axon terminal, a series of events take place that result in the release of neurotransmitter from the presynaptic axon. Select the answer that correctly describes the primary stimulus for vesicles to move
voltage-gated membrane channels open, and Ca+2 enters the cytoplasm, increasing intracellular calcium
Which statement best describes exocytosis?
Membrane organelles fuse with the membrane and release contents out of the cell.
What conditions will increase the diffusion of molecules, such as neurotransmitters?
An increase in the amount of neurotransmitter exocytized by the presynaptic axon.
If the membrane of a postsynaptic dendrite is setting up a graded potential, what must have happened after neurotransmitter was released by the presynaptic terminal?
bound at postsynaptic receptors to open postsynaptic ion channels.
Drag and drop the descriptive labels of events into the correct sequence at the chemical synapse.
1. action potential sweeps down presynaptic axon
2. calcium channels open in axon terminal
3. synaptic vesicles fuse and exocytize neurotransmitter
4. diffusion of neurotransmitter into ECF separating two neurons membranes
5. graded potentioal at postsyna
Which best represents synaptic transmission?
presynaptic axon to synapse to dendrite or postsynaptic cell body
Predict the possible effect of a drug that totally blocks the neurotransmitter receptor on the postsynaptic membrane.
For example, curare is a neurotoxin used by several South American cultures. The primary effect of curare is that acetylcholine, a major
Local graded potentials and action potential transmission is blocked and there is no response by the postsynaptic cell, the muscle.
Which ion channel opens in response to a change in membrane potential and participates in the generation and conduction of action potentials?
Which part of the neuron is responsible for generating a nerve impulse?
Which of the following types of glial cells produces the myelin sheaths that insulate axons, or nerve fibers, in the central nervous system (CNS)?
Where do most action potentials originate?
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.
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)
Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?
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 than the outside surface.
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.
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
What prevents the Na+ and K+ gradients from dissipating?
The small space between the sending neuron and the receiving neuron is the
A molecule that carries information across a synaptic cleft is a
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.
Which result of the stimulus applied is the likely cause of the response observed in the left graph?
opening of gated Na+ channels
When a sensory neuron is excited by some form of energy, the resulting graded potential is called a(n) ________.
Which of the following is not a function of the autonomic nervous system?
innervation of skeletal muscle
A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell?
Which component has a role in the postsynaptic cell during synaptic activity?
chemically gated channels
What is the role of calcium in synaptic activity?
Calcium influx into the synaptic terminal causes vesicle fusion.
What is the role of neurotransmitter at a chemical synapse?
Neurotransmitter binds to receptors on the postsynaptic cell membrane and allows ions to diffuse across the membrane.
Neurotransmitter is released from presynaptic neurons through what mechanism?
What type of channel on the postsynaptic membrane binds neurotransmitter?
a chemically gated channel
In addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity?
reuptake and degradation
Events that occur during synaptic activity are listed here, but they are arranged in an incorrect order. Choose the correct order of these events below. (a) Voltage-gated calcium channels open (b) Neurotransmitter binds to receptors (c) Action potential a
(c) Action potential arrives at axon terminal (a) Voltage-gated calcium channels open (e) Neurotransmitter released into synaptic cleft (b) Neurotransmitter binds to receptors (f) Graded potential generated in postsynaptic cell (d) Neurotransmitter is rem
Which of the following statements is true of both membrane potential responses shown in the graphs?
Both responses are examples of graded potentials.
Which of the following is not characteristic of neurons?
They are mitotic.
Which lettered region in the figure is referred to as the soma?
What is the role of acetylcholinesterase?
destroy ACh a brief period after its release by the axon endings
What event is depicted in the structure labeled A?
movement of Ca2+ into the interior of the axonal terminus through voltage-gated channels
Which of the following types of neurons carry impulses away from the central nervous system (CNS)?
Which of the following best describes the Na+ and K+ concentrations across a neuron's plasma membrane?
The Na+ concentration is higher outside the cell compared to inside. The K+ concentration is higher inside the cell compared to outside.
What is the major role of the Na+-K+ pump in maintaining the resting membrane potential?
maintaining the concentration gradients for Na+ and K+ across the cell membrane
Which of the following is the clearest example of a neuronal membrane's selective permeability?
K+ ions can diffuse across the membrane more easily than Na+ ions.
Which of the following would increase the membrane permeability to K+?
more K+ leakage channels
Suppose a drug is developed that blocks K+ leakage channels. The drug prevents ions from passing through those channels. If this drug was applied to a neuron, what would be the most immediate effect on that neuron?
The resting membrane potential would become less negative (more positive).
Imagine you changed the concentration of K+ outside a neuron such that the resting membrane potential changed to -80 mV (from the normal resting value of -70 mV). What have you changed?
the electrical gradient for K+ and the concentration gradient for K+
What is the electrochemical gradient of an ion?
the sum of the electrical and concentration gradients for that ion
Hypothetically, what would be the most immediate effect of doubling the number of Na+ leakage channels in the plasma membrane?
The resting membrane potential would become less negative (more positive).
Select the correct statement regarding synapses.
The synaptic cleft prevents an impulse from being transmitted directly from one neuron to another.
Which of the following statements most accurately describes the effects caused by binding of the ligand shown to the structure labeled C?
The membrane potential of the postsynaptic membrane changes.
The __________ is due to the difference in K+ and Na+ concentrations on either side of the plasma membrane, and the difference in permeability of the membrane to these ions.
resting membrane potential
The part of a neuron that conducts impulses away from its cell body is called a(n) ________.
Which of the choices below describes the ANS?
motor fibers that conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands
The substance released at axon terminals to propagate a nervous impulse is called a(n) ________.
Which of the following most accurately describes the involvement of the structure labeled B in synaptic signaling?
release of neurotransmitter into the synaptic cleft by exocytosis
What part of the nervous system performs information processing and integration?
central nervous system
Saltatory conduction is made possible by ________.
the myelin sheath
Neuroglia that control the chemical environment around neurons by buffering ions such as potassium and recapturing and recycling neurotransmitters are ________.
Which of the neuroglial cell types shown is the most abundant in the CNS?
If a motor neuron in the body were stimulated by an electrode placed about midpoint along the length of the axon ________.
the impulse would spread bidirectionally
Which of the neuroglial cell types shown are found in the PNS?
Which of the following is a factor that determines the rate of impulse propagation, or conduction velocity, along an axon?
degree of myelination of the axon
What does the central nervous system use to determine the strength of a stimulus?
frequency of action potentials
Which of the following is NOT one of the basic functions of the nervous system?
regulation of neurogenesis
What major ion currents occur at the point along the action potential phase labeled D?
diffusion of K+ out of the axon through gated ion channels
A neuron that has as its primary function the job of connecting other neurons is called a(n) ________.
Numerous nerve impulses arriving at a synapse at closely timed intervals exert a cumulative effect
Simultaneous stimulation of many terminals, distributed widely over the surface of a postsynaptic neuron
An insufficient stimulus
Any stimulus above this intensity will result in an action potential in a neuron
In which area of the neuron is an action potential initially generated?
at the axon hillock
The period after an initial stimulus when a neuron is not sensitive to another stimulus is the ________.
absolute refractory period
Which of the following membrane regions would have significant numbers of voltage-gated Na+ and K+ ion channels?
C and D
A second nerve impulse cannot be generated until ________.
the membrane potential has been reestablished
The box labeled D illustrates three mechanisms by which the effects of a neurotransmitter may be terminated. Which of the following mechanisms is NOT included in the figure?
reuptake of the neurotransmitter by transport into the postsynaptic cell
An impulse from one nerve cell is communicated to another nerve cell via the ________.
Which of the following is true of axons?
A neuron can have only one axon, but the axon may have occasional branches along its length.
Which area would contain an abundance of vesicles containing neurotransmitter?
synaptic vesicles with axon terminals for release into the synaptic cleft
Which of the following describes the nervous system integrative function?
analyzes sensory information, stores information, makes decisions
Schwann cells are functionally similar to ________.
Which of the following peripheral nervous system (PNS) neuroglia form the myelin sheaths around larger nerve fibers in the PNS?
Destruction of which of the neuroglial cell types leads to the disease multiple sclerosis (MS)?
Which of the following is false or incorrect?
A nerve impulse occurs if the excitatory and inhibitory effects are equal.
At which of the points along the illustrated action potential can a second action potential be produced, but only with a stimulus significantly greater than that which produced the first?
relative refractory period
The term central nervous system refers to the ________.
brain and spinal cord
Which of the following will occur when an excitatory postsynaptic potential (EPSP) is being generated on the dendritic membrane?
A single type of channel will open, permitting simultaneous flow of sodium and potassium.
Which of the following is the conducting region of the neuron?
Which of the neuroglial cell types shown control the flow of cerebrospinal fluid within the CNS?
The diffusion of what ion, across the neuronal membrane, is responsible for the local currents that depolarize regions of the axon to threshold?
An action potential in one segment of axon causes adjacent sections of axon membrane to reach threshold through what mechanism?
the generation of local currents
During action potential propagation in an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction?
The previous axonal segment is in the refractory period.
In a myelinated axon, how do the nodes of Ranvier differ from other segments of the same axon?
The nodes are more permeable to ions.
Where are action potentials regenerated as they propagate along a myelinated axon?
at the nodes of Ranvier
How do action potential propagation speeds compare in myelinated and unmyelinated axons?
Propagation is faster in myelinated axons.
The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.
The myelin on myelinated neurons can be degraded or destroyed in diseases such as multiple sclerosis-a process called demyelination. If a myelinated neuron was affected by demyelination, how would this affect action potentials in that neuron?
The speed of action potential propagation would be slower.
Unmyelinated fibers conduct impulses faster than myelinated fibers.
Which of the following are gaps found along a myelin sheath?
nodes of Ranvier
Which of the following types of glial cells monitors the health of neurons, and can transform into a special type of macrophage to protect endangered neurons?
What are ciliated CNS neuroglia that play an active role in moving the cerebrospinal fluid called?
What type of conduction takes place in unmyelinated axons?
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
Which of the neuroglial cell types shown form myelin sheaths within the CNS?
Opening K+ or Cl- channels in a postsynaptic membrane would produce an inhibitory postsynaptic potential (IPSP).
Which of the following is true regarding a response to an excitatory event which might occur soon after the initial stimulus indicated in the graph?
An excitatory event may result in an action potential, but this will be less likely if the excitatory stimulus occurs during the response to the stimulus observed in the graph.
What change in a neuron is being measured in the graph?
the voltage measured across the axon membrane at a specific point as an action potential travels past
The neuron cannot respond to a second stimulus no matter how strong
Absolute refractory period
The interior of the cell becomes less negative due to an influx of sodium ions
The specific period during which potassium ions diffuse out of the neuron due to a change in membrane permeability
Also called a nerve impulse transmitted by axons
An exceptionally strong stimulus can trigger a response
Relative refractory period
At which point of the illustrated action potential are the most gated Na+ channels open?
Voltage-gated Na+ channels open when the membrane potential reaches threshold and soon close when temporarily inactivated during the repolarization phase (C).
What structural classification describes this neuron?
The neuron shown has a many processes (axons and dendrites) that emerge from the cell body. Such a neuron is described as multipolar and typically functions as a motor neuron or interneuron.
Signals generated at a chemical synapse are said to move only in the direction of the presynaptic cell to the postsynaptic cell. Which of the following statements regarding the mechanisms determining this one way transmission is INCORRECT?
Ions diffusing out of the presynaptic cell can enter the postsynaptic cell, but cannot reenter the presynaptic cell.
Local anesthetics block voltage-gated Na+ channels, but they do not block mechanically gated ion channels. Sensory receptors for touch (and pressure) respond to physical deformation of the receptors, resulting in the opening of specific mechanically gated
Touch stimulation of this sensory receptor will open the mechanically gated ion channels, but action potentials are still not initiated because propagation of an action potential requires the opening of voltage-gated Na+ channels.
Which of the following is NOT a difference between graded potentials and action potentials?
Spatial summation is used to increase the amplitude of a graded potential; temporal summation is used to increase the amplitude of an action potential.
Which neurotransmitter(s) is/are the body's natural pain killer?
Neurons are also called nerve cells.
In what way does the interior surface of a cell membrane of a resting (nonconducting) neuron differ from the external environment? The interior is ________.
negatively charged and contains less sodium
Immediately after an action potential has peaked, which cellular gates open?
In multiple sclerosis, the cells that are the target of an autoimmune attack are the _________.
Oligodendrocytes are a type of neuroglial cell that function to form the myelin sheath around the axons of neurons within the central nervous system.
Which neuroglia are the most abundant and versatile of the glial cells?
Area where nerve impulse is generated.
Plasma membrane exhibits voltage-gated Na+ and K+ channels.
Plasma membrane exhibits voltage-gated Ca2+ channels.
Axon terminals release neurotransmitters.
Plasma membrane exhibits chemically gate ion channels.
During the action potential of a neuron, which ion is primarily crossing the membrane during the depolarization phase, and in which direction is the ion moving?
Na+ is entering the cell.
What is happening to voltage-gated channels at this point in the action potential?
Na+ channels are inactivating, and K+ channels are opening.
During what part of the action potential do voltage-gated Na+ channels begin to inactivate (their inactivation gates close)?
at the end of the depolarization phase, as the membrane potential approaches its peak value
The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by __________.
K+ ions leaving the cell through voltage-gated channels
During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________.
K+ ions diffusing through voltage-gated channels
During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels?
K+ channels close. Na+ channels go from an inactivated state to a closed state.
Tetraethylammonium (TEA) blocks voltage-gated K+ channels such that K+ cannot pass even when the channels are open. However, TEA leaves K+ leakage channels largely unaffected. How would you expect the action potential to change if you treated a neuron wit
The action potential would depolarize as usual, but the repolarization phase would take longer, causing the action potential to be more broad in time.
Which of the following is NOT one of the chemical classes into which neurotransmitters fall?
What type of stimulus is required for an action potential to be generated?
a threshold level depolarization
Which membrane potential occurs because of the influx of Na+ through chemically gated channels in the receptive region of a neuron?
excitatory postsynaptic potential
Which of the following is an excitatory neurotransmitter secreted by motor neurons innervating skeletal muscle?
Which of the following mechanisms is most significant in returning the membrane potential to the resting state (from point D to point E)?
closure of the voltage-gated K+ channels
In a synapse, neurotransmitters are stored in vesicles located in the __________.
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?