Anatomy and Physiology Chapter 11 Mastering Questions
The membrane potential is moving from a more positive value toward resting membrane potential:
Repolarize
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.
Which neuron circuit pattern is involved in the control of rhythmic activities such as breathing?
reverberating circuit
Which areas of this neuron would be classified as receptive regions?
Both A and B
The primary determinant of the resting membrane potential:
K+ permeability
The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____.
K+; Na+
Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?
Leak channels
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.
Although it plays a role, it is not a primary determinant of the resting membrane potential:
Na+ permeability
What prevents the Na+ and K+ gradients from dissipating?
Na+-K+ ATPase
What is the direct role of neurotransmitter at a chemical synapse?
Neurotransmitter binds to receptors on the postsynaptic cell membrane and allows ions to diffuse across the membrane.
Drag the charges to the correct side of the membrane to represent the resting membrane potential of a typical neuron.
Outside: positive (+) Inside: negative (-)
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)
T or F? Large-diameter nerve fibers conduct impulses much faster than small-diameter fibers.
T
T or F? Opening K+ or Cl- channels in a postsynaptic membrane would produce an inhibitory postsynaptic potential (IPSP).
T
T or F? Reflexes are rapid, automatic responses to stimuli.
T
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.
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 with TEA?
The action potential would depolarize as usual, but the repolarization phase would take longer, causing the action potential to be more broad in time.
A patient is admitted to the hospital with exacerbation of multiple sclerosis (MS). She asks the nurse "Why did this have to happen to me again? I was doing so well." Why are some forms of MS characterized by periods of remission and exacerbation?
The axons are not damaged; growing numbers of sodium channels appear spontaneously in the demyelinated fibers, allowing conduction to resume.
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 positive until the RMP reaches 0mV. Assuming that Na+ and K+ are the major determinants of RMP in this cell, which of the following could best explain your results?
The cell's Na+−K+ ATPase pumps have stopped functioning.
Where in the neuron is an action potential initially generated?
axon hillock
Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.
chemically gated; postsynaptic
Which of the following is NOT one of the chemical classes into which neurotransmitters fall?
chlorides
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 types of glial cells produces the myelin sheaths that insulate axons, or nerve fibers, in the central nervous system (CNS)?
oligodendrocytes
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
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
Which of the following circuit types is involved in the control of rhythmic activities such as the sleep-wake cycle, breathing, and certain motor activities (such as arm swinging when walking)?
reverberating circuits
The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.
saltatory conduction
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+
This neuron is most depolarized at __________ mV.
+30
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 extracellular fluid separating two neurons' membranes. 5) Graded potential of postsynaptic membrane.
Destruction of which of the neuroglial cell types leads to the disease multiple scleroses (MS)?
A
Which of the neuroglial cell types shown form myelin sheaths within the CNS?
A
At which point of the illustrated action potential are the most gated Na+ channels open?
B
Which lettered region in the figure is referred to as the soma?
B
Which of the neuroglial cell types shown is the most abundant in the CNS?
B
In which area of the neuron is an action potential initially generated?
C
Which of the neuroglial cell types shown control the flow of cerebrospinal fluid within the CNS?
D
Which area would contain an abundance of vesicles containing neurotransmitter?
E
T or F? Strong stimuli cause the amplitude of action potentials generated to increase.
F
T or F? The all-or-none phenomenon as applied to nerve conduction states that the whole nerve cell must be stimulated for conduction to take place.
F
T or F? The nodes of Ranvier are found only on myelinated, peripheral neuron processes.
F
Which of the following is NOT true of association neurons?
Most association neurons are confined within the peripheral nervous system (PNS).
Sort the phrases into the appropriate bins depending on whether they describe similarities or differences between voltage-gated K+ channels and voltage-gated Na+ channels. If a phrase is not factually correct, drag it to the "Incorrect" bin.
Similarities: The stimulus that triggers opening, The polarity of the substances they transport across the membrane, The placement of the channel protein relative to the membrane Differences: The direction of ion movement through the channel, The inactivation mechanism Incorrect: Both channels have inactivation gates, They move Na+ and K+ in the same direction
What type of channel on the postsynaptic membrane binds neurotransmitter?
a chemically gated channel
The period after an initial stimulus when a neuron is not sensitive to another stimulus is the ________.
absolute refractory period
Cold sores on the skin of the mouth occur when herpes simplex viruses that are dormant in neural ganglia become active and travel to the skin of the mouth. Which of the following is the mechanism by which these viruses travel from the ganglia (located within the head) to the skin of the mouth?
anterograde axonal transport
During depolarization, which gradient(s) move(s) Na+ into the cell?
both the electrical and chemical gradients
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.
During the action potential, when does sodium permeability initially DECREASE?
during the peak of depolarization
Which of the following neurotransmitters inhibits pain and is mimicked by morphine, heroin, and methadone?
endorphin
Which neurotransmitter(s) is/are the body's natural pain killer?
endorphins
Which of the following is true about the movement of ions across excitable living membranes?
Sodium gates in the membrane can open in response to electrical potential changes.
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.
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?
microglia
Which of the following would increase the membrane permeability to K+?
more K+ leakage channels
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
A molecule that carries information across a synaptic cleft is a
neurotransmitter.
Which of the following are gaps found along a myelin sheath?
nodes of Ranvier
Which of the following is not a chemical class of neurotransmitters?
nucleic acid
Which result of the stimulus applied is the likely cause of the response observed in the left graph?
opening of gated Na+ channels
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
Immediately after an action potential has peaked, which cellular gates open?
potassium
Which of the following is NOT a type of circuit?
pre-discharge circuits
Which best represents synaptic transmission?
presynaptic axon to synapse to dendrite or postsynaptic cell body
Which of the following is not a function of astrocytes?
provide the defense for the CNS
Which of the following is NOT one of the basic functions of the nervous system?
regulation of neurogenesis
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
Which pattern of neural processing works in a predictable, all-or-nothing manner, where reflexes are rapid and automatic responses to stimuli in which a particular stimulus always causes the same response?
serial processing
Which of the following describes the excitatory postsynaptic potential?
short distance depolarization
An impulse from one nerve cell is communicated to another nerve cell via the ________.
synapse
The small space between the sending neuron and the receiving neuron is the
synaptic cleft.
Which criterion is used to functionally classify neurons?
the direction in which the nerve impulse travels relative to the central nervous system
A second nerve impulse cannot be generated until ________.
the membrane potential has been reestablished
Saltatory conduction is made possible by ________.
the myelin sheath
T or F? Myelination of the nerve fibers in the central nervous system is the job of the oligodendrocyte.
T
T or F? Neurons in the CNS are organized into functional groups.
T
T or F? The oligodendrocytes can myelinate several axons.
T
T or F? The overlapping functions of the nervous system are sensory input, integration, and motor output.
T
T or F? Unipolar neurons have axons structurally divided into peripheral and central processes.
T
The part of a neuron that conducts impulses away from its cell body is called a(n) ________.
axon
Which of the following is the conducting region of the neuron?
axon
An inhibitory postsynaptic potential (IPSP) is associated with ________.
hyperpolarization
Which of the following is not a function of the autonomic nervous system?
innervation of skeletal muscle
What component of the reflex arc determines the response to a stimulus?
integration center
At which membrane potential, given the graphs shown, do a sufficient number of the voltage-gated Na+ channels start to open?
-60 mV
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 __________.
-70 mV
This cell reaches threshold at approximately __________ msec.
0.6
What is the magnitude (amplitude) of an action potential?
100 mV
This neuron spends approximately __________ msec in a hyperpolarized state.
2.5
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.
Which of the following is false or incorrect?
A nerve impulse occurs if the excitatory and inhibitory effects are equal.
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.
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.
C A E B F D (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 removed from the synaptic cleft
Which of the following membrane regions would have significant numbers of voltage-gated Na+ and K+ ion channels?
C and D
What is the role of calcium in synaptic activity?
Calcium influx into the synaptic terminal causes vesicle fusion.
Based on your knowledge of action potentials in neurons, what can you conclude about how they occur in cardiac muscle fibers?
Cardiac muscle fibers depolarize more quickly and spend more time depolarized than neurons do.
What type of conduction takes place in unmyelinated axons?
Continuous conduction
The membrane potential is more negative than the resting membrane potential:
Hyperpolarize
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.
Where do most action potentials originate?
Initial segment
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.
In which type of axon will velocity of action potential conduction be the fastest?
Myelinated axons with the largest diameter
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.
How do action potential propagation speeds compare in myelinated and unmyelinated axons?
Propagation is faster in myelinated axons.
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.
T or F? A postsynaptic potential is a graded potential that is the result of a neurotransmitter released into the synapse between two neurons.
T
Which of the stimuli in this experiment would be considered a threshold stimulus?
Stimulus 2
T or F? A stimulus traveling toward a synapse appears to open calcium ion channels at the presynaptic end, which in turn promotes fusion of synaptic vesicles to the axonal membrane.
T
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.
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 than the outside surface.
What characterizes depolarization, the first phase of the action potential?
The membrane potential changes from a negative value to a positive value.
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.
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.
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.
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.
A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell?
a neuron
The velocity of the action potential is fastest in which of the following axons?
a small myelinated axon
What type of stimulus is required for an action potential to be generated?
a threshold level depolarization
Which of the following correctly describes a graded potential?
amplitude of various sizes
Which of the following describes the nervous system integrative function?
analyzes sensory information, stores information, makes decisions
A neuron that has as its primary function the job of connecting other neurons is called a(n) ________.
association neuron
Neuroglia that control the chemical environment around neurons by buffering potassium and recapturing neurotransmitters are ________.
astrocytes
Which neuroglia are the most abundant and versatile of the glial cells?
astrocytes
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
Where are action potentials regenerated as they propagate along a myelinated axon?
at the nodes of Ranvier
What part of the nervous system performs information processing and integration?
central nervous system
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
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
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
What is the role of acetylcholinesterase?
destroy ACh a brief period after its release by the axon endings
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
What are ciliated CNS neuroglia that play an active role in moving the cerebrospinal fluid called?
ependymal cells
Neurotransmitter is released from presynaptic neurons through what mechanism?
exocytosis
Bipolar neurons are commonly ________.
found in the retina of the eye
What does the central nervous system use to determine the strength of a stimulus?
frequency of action potentials
Collections of nerve cell bodies outside the central nervous system are called ________.
ganglia
When a sensory neuron is excited by some form of energy, the resulting graded potential is called a(n) ________.
generator potential
Which of the following types of neurons carry impulses away from the central nervous system (CNS)?
motor
Which of the choices below describes the ANS?
motor fibers that conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands
What event is depicted in the structure labeled A?
movement of Ca2+ into the interior of the axonal terminus through voltage-gated channels
Complete the following sentence. The operation of the Na+−K+ ATPase pump __________.
moves 3 Na+ to the ECF and 2 K+ to the cytoplasm
What structural classification describes this neuron?
multipolar
Which of the following is NOT a functional classification of neurons?
multipolar
Saltatory propagation occurs in _________ axons, in which action potentials _________.
myelinated; move from one node of Ranvier to another
In multiple sclerosis, the cells that are the target of an autoimmune attack are the _________.
oligodendrocytes
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
Cold sores on the skin of the mouth occur when herpes simplex viruses that are dormant in neural ganglia become active and travel to the skin of the mouth. Which of the following is the mechanism by which these viruses travel from the ganglia (located within the head) to the skin of the mouth?
retrograde transport
In addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity?
reuptake and degradation
Hyperpolarization results from __________.
slow closing of voltage-gated K+ channels
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
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
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.
During an action potential, the rapid decrease in sodium permeability and simultaneous increase in potassium permeability is responsible for __________.
the repolarization phase
Which of the following allows us to consciously control our skeletal muscles?
the somatic nervous system
What structural classification describes the neuron associated with the neuroglia shown by E and F?
unipolar
An action potential releases neurotransmitter from a neuron by opening which of the following channels?
voltage-gated Ca2+ channels
The depolarization phase of an action potential results from the opening of which channels?
voltage-gated Na+ channels
Which ion channel opens in response to a change in membrane potential and participates in the generation and conduction of action potentials?
voltage-gated channel
The generation of an action potential in a neuron requires the presence what type of membrane channels?
voltage-gated channels
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 towards the cell membrane and eventually release their contents.
voltage-gated membrane channels open, and Ca+2 enters the cytoplasm, increasing intracellular calcium
T or F? Some neurotransmitters can be either excitatory or inhibitory depending upon the receptor.
T
T or F? The action potential is caused by permeability changes in the plasma membrane.
T
T or F? The autonomic nervous system is under voluntary control; whereas, the somatic nervous system is involuntary.
F
T or F? 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.
F
T or F? Unmyelinated fibers conduct impulses faster than myelinated fibers.
F
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.
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.
During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________.
K+ ions diffusing through voltage-gated channels
Select the correct statement regarding synapses.
The synaptic cleft prevents an impulse from being transmitted directly from one neuron to another.
Schwann cells are functionally similar to ________.
oligodendrocytes
What is the value for the resting membrane potential for most neurons?
-70 mV
What is the resting membrane potential of the neuron used in the experiment?
-80 mV
Place the action potential events below in the correct sequence. If two events occur simultaneously, place one on top of the other.
1) Activation gates on Na+ channels open; Na+ enters cell 2) Cell depolarizes 3) Inactivation gates on Na+ channels close AND Activation gates on K+ channels open; K+ leaves cell 4) Cell repolarizes 5) Activation gates on K+ channels begin to close 6) Cell experiences hyperpolarization
Drag the labels to identify the sequence of events that occurs at a synapse.
1) An action potential arrives at the synaptic terminal. 2) Calcium channels open, and calcium ions enter the synaptic terminal. 3) Vesicles containing neurotransmitter fuse with the plasma membrane of the sending neuron. 4) Neurotransmitter molecules diffuse across the synaptic cleft. 5) The neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron, causing ion channels there to open.
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 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 conditions will increase the diffusion of molecules, such as neurotransmitters?
An increase in the amount of neurotransmitter exocytized by the presynaptic axon.
How is an action potential propagated along an axon?
An influx of sodium ions from the current action potential depolarizes the adjacent area.
Which of the following statements is true of both membrane potential responses shown in the graphs?
Both responses are examples of graded potentials.
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?
D
The membrane potential is becoming more positive than the resting membrane potential:
Depolarize
Which of the neuroglial cell types shown are found in the PNS?
E
The concentration of __________ is higher inside than outside the cell.
K+
The ion __________ is crossing the cell's plasma membrane at 1.5 msec.
K+
The membrane is more permeable to __________.
K+
The resting membrane potential is maintained by Na+-K+ pumps that actively transport __________ into and __________ out of the cell.
K+ ; Na+
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
Which of the following peripheral nervous system (PNS) neuroglia form the myelin sheaths around larger nerve fibers in the PNS?
Schwann cells
T or F? Axon diameter and degree of myelination determine nerve impulse conduction velocity.
T
T or F? Cell bodies of sensory neurons may be located in ganglia lying outside the central nervous system.
T
T or F? During depolarization, the inside of the neuron's membrane becomes less negative.
T
T or F? Efferent nerve fibers may be described as motor nerve fibers.
T
T or F? Enkephalins and endorphins are peptides that act like morphine.
T
T or F? If bacteria invaded the CNS tissue, microglia would migrate to the area to engulf and destroy them.
T
T or F? In myelinated axons the voltage-regulated sodium channels are concentrated at the nodes of Ranvier.
T
T or F? Neurons are also called nerve cells.
T
What does 0 mV on the Y-axis of an action potential tracing represent?
The cell's membrane is at equilibrium.
Match each phase of an action potential with the states of the ion channels you have studied: resting state
Voltage-gated Na+ Channels: closed Voltage-gated K+ Channels: closed
What opens first in response to a threshold stimulus?
Voltage-gated Na+ channels
Which of the following mechanisms is most significant in returning the membrane potential to the resting state (from point D to point E)?
active transport by the Na+-K+ pump
Which part of the neuron is responsible for generating a nerve impulse?
axon
What is the electrochemical gradient of an ion?
the sum of the electrical and concentration gradients for that ion
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
In a synapse, neurotransmitters are stored in vesicles located in the __________.
presynaptic neuron
You are working on a new medication to selectively kill cancer cells. You test the drug on a culture of normal neurons to check for any side effects. Despite the presence of the drug, a normal resting membrane potential of −70 mV is maintained. Look at each of the figures below to analyze how the drug might be affecting the neuron. Figure A shows neuron activity under normal, or control, conditions (without the drug). Figure B shows neuron activity that has been altered due to exposure to the drug. Based on these results, the drug is most likely __________.
preventing Na+-gated channels from opening
Which of the following best characterizes depolarization?
small consecutive steps of Na+ penetration into the axon along its length
The repolarization phase of an action potential results from __________.
the opening of voltage-gated K+ channels
The term central nervous system refers to the ________.
brain and spinal cord
Binding of the neurotransmitter to its receptor causes the membrane to __________.
either depolarize or hyperpolarize
Which of the following are bundles of neurofilaments that are important in maintaining the shape and integrity of neurons?
neurofibrils
The substance released at axon terminals to propagate a nervous impulse is called a(n) ________.
neurotransmitter
Which component has a role in the postsynaptic cell during synaptic activity?
chemically gated channels
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. Drag the appropriate items to their respective bins.
More Positive: Triple the number of Na+ leak channels ; Double the concentration of K+ outside the cell More Negative: Double the number of K+ leak channels ; Decrease the concentration of Na+ outside the cell by half Largely Unchanged: Double the size of the cell, without adding channels ; Double the number of closed channels for K+
The concentration of __________ is higher outside than inside the cell.
Na+
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.
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
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.
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).
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).
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.
Which of the following is NOT true of an electrical synapse?
They are specialized for release and reception of chemical neurotransmitters.
Which of the following is not true of graded potentials?
They increase amplitude as they move away from the stimulus point.
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 ion channels. Why does injection of a local anesthetic into a finger still cause a loss of the sensation of touch from the finger?
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 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.
Match each phase of an action potential with the states of the ion channels you have studied: hyperpolarization
Voltage-gated Na+ Channels: closed Voltage-gated K+ Channels: open
Match each phase of an action potential with the states of the ion channels you have studied: repolarization
Voltage-gated Na+ Channels: inactivated Voltage-gated K+ Channels: open
Match each phase of an action potential with the states of the ion channels you have studied: depolarization
Voltage-gated Na+ Channels: open Voltage-gated K+ Channels: closed
What is the first change to occur in response to a threshold stimulus?
Voltage-gated Na+ channels change shape, and their activation gates open.
Following repolarization, the neuron may become slightly hyperpolarized before it re-establishes its resting membrane potential. Hyperpolarization is due to a difference between how the voltage-gated Na+ and K+ channels work. What is this difference?
Voltage-gated Na+ channels stop the flow of Na+ relatively quickly, while voltage-gated K+ channels are slow to close, resulting in the overshoot.
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 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 statement best describes exocytosis?
Membrane organelles fuse with the membrane and release contents out of the cell.
Place the events involved in the propagation of an action potential in the correct order of occurrence from left to right.
1) Local current flows to axon segment 2) Axon segment depolarized to threshold 3) Voltage-gated Na+ channels open 4) Influx of Na+ 5) AP regenerated in adjacent axon segment
Order each of the following events so that they occur in the proper order, from left to right, with respect to the function of the channels, ion permeability, and changes in membrane potential.
1) Opening of voltage-gated Na+ channels 2) Na+ ion flow into the neuron increases 3) Depolarization of the membrane to +30 mV 4) K+ ion flow out of the neuron increases 5) Repolarization of the membrane
Place the events involved in generation of an action potential in the correct order of occurrence from left to right.
1) Threshold stimulus, Na+ channels open 2) Na+ influx, Depolarization 3) Na+ channels close, K+ channels open 4) K+ efflux, Repolarization 5) Hyperpolarization, K+ channels close
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 neuromuscular neurotransmitter, cannot bind at its receptor because curare is blocking it. Predict the possible effects of curare on the postsynaptic membrane and muscle.
Local graded potentials and action potential transmission is blocked and there is no response by the postsynaptic cell, the muscle.
The resting membrane potential of the cell:
Membrane potential of −70 mV
The point at which there is no net movement of K+ into or out of the cell:
Membrane potential of −90 mV
The diffusion of what ion, across the neuronal membrane, is responsible for the local currents that depolarize regions of the axon to threshold?
Na+ (sodium)
The concentrations of which two ions are highest outside the cell.
Na+ and Cl-
The concentrations of which two ions are highest outside the cell?
Na+ and Cl−
What is happening to voltage-gated channels at this point in the action potential?
Na+ channels are inactivating, and K+ channels are opening.
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.
Which of the following is not characteristic of neurons?
They are mitotic.
Which of the following is an excitatory neurotransmitter secreted by motor neurons innervating skeletal muscle?
acetylcholine