What type of conduction takes place in unmyelinated axons?
Synaptic transmission
Saltatory conduction
Continuous conduction
Electrical conduction
answer
continuous conduction
rationale: An action potential is conducted continuously along an unmyelinated axon from its initial segment to the axon terminals. The term continuous refers to the fact that the action potential is regenerated when voltage-gated Na+ channels open in every consecutive segment of the axon, not at nodes of Ranvier.
question
An action potential is self-regenerating because __________.
repolarizing currents established by the efflux of Na+ flow down the axon and trigger an action potential at the next segment
repolarizing currents established by the efflux of K+ flow down the axon and trigger an action potential at the next segment
depolarizing currents established by the influx of K+ flow down the axon and trigger an action potential at the next segment
depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment
answer
depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment
rationale: The Na+ diffusing into the axon during the first phase of the action potential creates a depolarizing current that brings the next segment, or node, of the axon to threshold.
question
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.
The inactivation gates of voltage-gated K+ channels close in the node, or segment, that has just fired an action potential.
The activation gates of voltage-gated K+ channels open in the node, or segment, that has just depolarized.
The activation gates of voltage-gated Na+ channels close in the node, or segment, that has just depolarized.
answer
The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential.
rationale: At the peak of the depolarization phase of the action potential, the inactivation gates close. Thus, the voltage-gated Na+ channels become absolutely refractory to another depolarizing stimulus.
question
What is the function of the myelin sheath?
The myelin sheath decreases the speed of action potential conduction from the initial segment to the axon terminals.
The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.
The myelin sheath increases the insulation along the entire length of the axon.
The myelin sheath decreases the resistance of the axonal membrane to the flow of charge.
answer
The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.
rationale: The myelin sheath increases the velocity of conduction by two mechanisms. First, myelin insulates the axon, reducing the loss of depolarizing current across the plasma membrane. Second, the myelin insulation allows the voltage across the membrane to change much faster. Because of these two mechanisms, regeneration only needs to happen at the widely spaced nodes of Ranvier, so the action potential appears to jump.
question
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.
Activation gates of voltage-gated Na+ channels close, while inactivation gates of voltage-gated K+ channels open.
Activation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.
Inactivation gates of voltage-gated Na+ channels close, while inactivation gates of voltage-gated K+ channels open.
answer
Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.
rationale: Closing of voltage-gated channels is time dependent. Typically, the inactivation gates of voltage-gated Na+ channels close about a millisecond after the activation gates open. At the same time, the activation gates of voltage-gated K+ channels open.
question
In which type of axon will velocity of action potential conduction be the fastest?
Myelinated axons with the largest diameter
Unmyelinated axons with the largest diameter
Unmyelinated axons of the shortest length
Myelinated axons with the smallest diameters
answer
Myelinated axons with the largest diameter
rationale: The large diameter facilitates the flow of depolarizing current through the cytoplasm. The myelin sheath insulates the axons and prevents current from leaking across the plasma membrane.
question
The small space between the sending neuron and the receiving neuron is the
synaptic cleft.
synaptic terminal.
vesicle.
calcium channel.
neurotransmitter.
answer
synaptic cleft
rationale: The synaptic cleft is the small space between the sending neuron and the receiving neuron.
question
A molecule that carries information across a synaptic cleft is a
receiving neuron.
sending neuron.
neurotransmitter.
synaptic cleft.
synapse.
answer
neurotransmitter
rationale: Neurotransmitter molecules carry information across a synaptic cleft.
question
When calcium ions enter the synaptic terminal,
neurotransmitter molecules are quickly removed from the synaptic cleft.
they cause an action potential in the sending neuron.
the inside of the receiving neuron becomes more positive.
the inside of the receiving neuron becomes more negative.
they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.
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,
vesicles in the synaptic terminal fuse to the plasma membrane of the sending neuron.
the receiving neuron becomes more negative inside.
ion channels in the plasma membrane of the sending neuron open.
ion channels in the plasma membrane of the receiving neuron open.
the receiving neuron becomes more positive inside.
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,
the receiving neuron immediately generates an action potential.
the sending neuron becomes more negative inside.
the sending neuron becomes more positive inside.
the receiving neuron is less likely to generate an action potential.
the receiving neuron is more likely to generate an action potential.
answer
the receiving neuron is less likely to generate an action potential.
rationale: If the receiving neuron is more negative inside, it is less likely to generate an action potential.
question
The generation of an action potential in a neuron requires the presence what type of membrane channels?
voltage-gated channels
leakage channels
chemically gated channels
membrane channels are not required
answer
voltage-gated channels
question
Saltatory propagation occurs in _________ axons, in which action potentials _________.
unmyelinated; spread by depolarizing the adjacent region of the axon membrane
myelinated; move continuously along the axon toward the axon hillock
myelinated; move from one node of Ranvier to another
unmyelinated; move from one node of Ranvier to another
answer
myelinated; move from one node of Ranvier to another
rationale: Saltatory propagation is much faster than continuous propagation. The speed of propagation along an axon varies in two ways: 1) myelin sheaths limit the movement of ions across the axon membrane, thereby requiring the action potentials to "leap" from node to node during propagation, thus traveling at a greater speed; and 2) the diameter of the axon directly relates to the speed of propagation (i.e., the larger the diameter of the axon, the faster the speed of propagation).
question
Where do most action potentials originate?
Axon terminal
Nodes of Ranvier
Initial segment
Cell body
answer
Initial segment
rationale: The first part of the axon is known as the initial segment. The initial segment is adjacent to the tapered end of the cell body, known as the axon hillock.
question
What opens first in response to a threshold stimulus?
Ligand-gated cation channels
Ligand-gated Cl- channels
Voltage-gated K+ channels
Voltage-gated Na+ channels
answer
Voltage-gated Na+ channels
rationale: The activation gates of voltage-gated Na+ channels open, and Na+ diffuses into the cytoplasm.
question
What characterizes depolarization, the first phase of the action potential?
The membrane potential changes to a much more negative value.
The membrane potential reaches a threshold value and returns to the resting state.
The membrane potential changes from a negative value to a positive value.
The membrane potential changes to a less negative (but not a positive) value.
answer
The membrane potential changes from a negative value to a positive value.
rationale: The plasma membrane, which was polarized to a negative value at the RMP, depolarizes to a positive value.
question
What characterizes repolarization, the second phase of the action potential?
Once the membrane depolarizes to a threshold value of approximately -55 mV, it repolarizes to its resting value of -70 mV.
As the membrane repolarizes to a negative value, it goes beyond the resting state to a value of -80 mV.
Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.
Before the membrane has a chance to reach a positive voltage, it repolarizes to its negative resting value of approximately -70 mV.
answer
Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.
rationale: The plasma membrane was depolarized to a positive value at the peak of the first phase of the action potential. Thus, it must repolarize back to a negative value.
question
What event triggers the generation of an action potential?
The membrane potential must hyperpolarize from the resting voltage of -70 mV to the more negative value of -80 mV.
The membrane potential must return to its resting value of -70 mV from the hyperpolarized value of -80 mV.
The membrane potential must depolarize from the resting voltage of -70 mV to its peak value of +30 mV.
The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.
answer
The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.
rationale: This is the minimum value required to open enough voltage-gated Na+ channels so that depolarization is irreversible.
question
What is the first change to occur in response to a threshold stimulus?
Voltage-gated Na+ channels change shape, and their inactivation gates close.
Voltage-gated Na+ channels change shape, and their activation gates open.
Voltage-gated Ca2+ channels change shape, and their activation gates open.
Voltage-gated K+ channels change shape, and their activation gates open.
answer
Voltage-gated Na+ channels change shape, and their activation gates open.
rationale: The activation gates of voltage-gated Na+ channels open very rapidly in response to threshold stimuli. The activation gates of voltage-gated K+ channels are comparatively slow to open.
question
Strong stimuli cause the amplitude of action potentials generated to increase.
True
False
answer
False
question
What type of stimulus is required for an action potential to be generated?
a suprathreshold stimulus
hyperpolarization
multiple stimuli
a threshold level depolariza
answer
a threshold level depolarization
rationale: The axolemma must be depolarized to threshold in order to generate an action potential.
question
A postsynaptic potential is a graded potential that is the result of a neurotransmitter released into the synapse between two neurons.
True
False
answer
True
question
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?
Positive membrane potential
Action potential
Resting membrane potential (RMP)
Threshold potential
answer
Resting membrane potential (RMP)
rationale: The resting membrane potential is the baseline potential that can be recorded across the plasma membrane of an excitable cell prior to excitation.
question
Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?
Voltage-gated channels
Leak channels
Sodium-potassium ATPases
Ligand-gated channels
answer
Leak channels
rationale: Leak channels for Na+ and K+ are ubiquitous, and they allow for the diffusion of these ions across plasma membranes.
question
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 positively charged than the inside surface.
The outside surface of the plasma membrane is much more negatively charged than the inside surface.
The inside surface of the plasma membrane is much more negatively charged than the outside surface.
There is no electrical potential difference between the inside and the outside surfaces of the plasma membrane.
answer
The inside surface of the plasma membrane is much more negatively charged than the outside surface.
rationale: The inside surface of the plasma membrane accumulates more negative charge because of the presence of Na+ and K+ gradients and the selective permeability of the membrane to Na+ and K+.
question
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.
There are many more voltage-gated K+ channels than voltage-gated Na+ channels.
Ligand-gated cation channels favor a greater influx of Na+ than K+.
The Na+-K+ pumps transport more K+ into cells than Na+ out of cells.
answer
There are many more K+ leak channels than Na+ leak channels in the plasma membrane.
rationale: More leak channels translates into more leakiness. Thus the outward flux of K+ is greater than the inward flux of Na+.
question
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 a resting membrane potential and leak channels
The presence of concentration gradients and leak channels
The presence of concentration gradients and Na+-K+ pumps
The presence of concentration gradients and voltage-gated channels
answer
The presence of concentration gradients and leak channels
rationale: the concentration gradient and the large number of K+ leak channels allow for rather robust K+ diffusion out of a cell. In contrast, the concentration gradient and the relatively few Na+ leak channels allow for much less Na+ diffusion into a cell.
question
What prevents the Na+ and K+ gradients from dissipating?
Na+-K+ ATPase
Na+ and K+ leaks
Na+ cotransporter
H+-K+ ATPase
answer
Na+-K+ ATPase
rationale: Also known as the Na+-K+ pump, or simply the pump, this transporter moves three Na+ out of the cell and two K+ into the cell for every ATP it hydrolyzes. This pumping action prevents the Na+ and K+ gradients from running down as these ions passively move through leak channels.
question
Which of the following is NOT one of the basic functions of the nervous system?
Integrate sensory input for decision making.
Release hormones into the bloodstream to communicate with other cells in the body.
Generate direct, electrical signals.
Decode sensory information from the environment.
answer
Release hormones into the bloodstream to communicate with other cells in the body.
rationale: Hormones are released by endocrine organs. The nervous system does have some control over endocrine function, but the endocrine system is considered a separate signaling system.
question
As you start working out, you notice that your heart rate and breathing rate start to increase. Which division of your nervous system is generating this response? Be as specific as possible.
the somatic nervous system
the afferent division of the nervous system
the sympathetic division of the autonomic nervous system
the parasympathetic division of the autonomic nervous system
answer
the sympathetic division of the autonomic nervous system
rationale: The sympathetic division of the autonomic, or involuntary, nervous system consists of visceral motor nerve fibers that regulate the activity of smooth muscles, cardiac muscles, and glands. This division is responsible for generating actions required during activity.
question
What division of the nervous system is most specifically responsible for voluntary motor control?
central nervous system
parasympathetic nervous system
somatic nervous system
sympathetic nervous system
answer
somatic nervous system
rationale: The somatic nervous system is composed of somatic motor nerve fibers that conduct impulses from the central nervous system to skeletal muscles. It is often referred to as the voluntary nervous system because it allows us to consciously control our skeletal muscles.
question
In which area of the neuron is an action potential initially generated?
answer
C
question
Many neurons have many short, branching extensions called dendrites. What is the benefit of these structures for a neuron?
The dendrites provide a large surface area for connections from other neurons.
There is a large amount of space for myelin to form and make electrical conduction more efficient.
There is a large area for production of chemicals used to signal other neurons.
There is a large surface area to send signals to other cells.
answer
The dendrites provide a large surface area for connections from other neurons.
rationale: because of the branching and extensive membrane surface area, there is a large amount of membrane dedicated to synapses with other neurons.
question
Bundles of neurons in the central nervous system are called tracts.
True
False
answer
True
question
Which criterion is used to functionally classify neurons?
whether the nerve fibers are myelinated or unmyelinated
whether the neurons are found within the CNS or the PNS
the number of processes extending from the cell body neuron
the direction in which the nerve impulse travels relative to the central nervous system
answer
the direction in which the nerve impulse travels relative to the central nervous system
rationale: Functional classification groups neurons according to the direction in which the nerve impulse travels relative to the central nervous system. Based on this criterion, there are sensory neurons, motor neurons, and interneurons.
question
Which is the main receptive portion of the neuron?
the dendrite
the cell body or soma
the axon
the synapse
answer
the dendrite
rationale: Dendrites are the main receptive or input regions, providing an enormous surface area for receiving signals from other neurons.
question
Cell bodies of sensory neurons may be located in ganglia lying outside the central nervous system.
True
False
answer
True
question
During depolarization, the inside of the neuron's membrane becomes less negative.
True
False
answer
True
question
If the neuron membrane becomes more permeable to Na+, Na+ will transport across the membrane, causing the cell to depolarize.
True
False
answer
True
rationale: In either a graded or action potential, Na+ is transported into the cell faster than during resting potentials. As Na+ enters the cell, the inside of the cell becomes more positive, or depolarized.
question
The action potential is caused by permeability changes in the plasma membrane.
True
False
answer
True
question
Ca2+, which then causes release of neurotransmitter from the axon terminal
answer
What ion is entering the axon terminal at A, and what effect does it have?
Ca2+, which then causes release of neurotransmitter from the axon terminal
Na+, which then causes repolarization of the axon terminal's membrane
neurotransmitter, which then causes the presynaptic neuron to form an action potential
K+, which then causes increased production of neurotransmitter
question
exocytosis
rationale: The influx of Ca2+ triggers the release of neurotransmitters stored in synaptic vesicles (B) by exocytosis.
answer
By which method does the structure at B release neurotransmitter?
passive diffusion
active transport
facilitated diffusion
exocytosis
question
chemically gated
rationale: The receptors at C are affected by the binding of a chemical neurotransmitter.
answer
How would the receptors at C best be classified?
chemically gated
voltage gated
mechanically gated
question
Both responses are examples of graded potentials.
rationale: Both responses are short-lived, relatively small changes in the membrane potential.
answer
Which of the following statements is true of both membrane potential responses shown in the graphs?
Both responses are examples of excitatory postsynaptic potentials (EPSPs).
Both responses are examples of graded potentials.
Both responses are examples of inhibitory postsynaptic potentials (IPSPs).
Both responses are examples of action potentials.
question
opening of gated Na+ channels
rationale: Opening of gated Na+ channels allows Na+ to diffuse into the neuron, causing an increase in the local membrane potential.
answer
Which of the following stimuli caused the reaction in the graph on the left?
opening of gated Ca2+ channels
opening of gated Cl- channels
opening of gated Na+ channels
opening of gated K+ channels
question
Opening K+ or Cl- channels in a postsynaptic membrane would produce an inhibitory postsynaptic potential (IPSP).
True
False
answer
True
rationale: Opening K+ or Cl- channels in a postsynaptic membrane, resulting in K+ efflux or Cl- influx, respectively, would induce hyperpolarization. As the membrane potential increases and is driven farther from the axon's threshold, the postsynaptic neuron becomes less and less likely to "fire," and larger depolarizing currents are required to induce an action potential (AP). Hyperpolarizing changes in potential are called inhibitory postsynaptic potentials (IPSPs).
question
What component of the reflex arc determines the response to a stimulus?
effector
integration center
receptor
sensory neuron
answer
integration center
rationale: The integration center receives sensory information (input), determines the proper response, and then signals the appropriate effector(s) to produce the response.
question
The nervous system has three overlapping functions. Which of the following represents a logical sequence of these three functions?
a. sensory input, motor output, integration
b. motor output, integration, sensory input
c. sensory input, integration, motor output
d. integration, sensory input, motor output
answer
c. sensory input, integration, motor output
question
While studying for an exam, you reach for a beverage. To extend your arm, your _______ nervous system is activated.
A. afferent
B. autonomic
C. sympathetic
D. somatic
answer
D. somatic
question
The portion of an axon that communicates with its target cells is the ______.
A. dendrite
B. axon
C. axon terminal
D. cell body
answer
C. axon terminal
question
A change in membrane potential from -70 to -40 would be termed _______.
A. repolarization
B. depolarization
C. hyperpolarization
D. hypopolarization
answer
B. depolarization
question
Sodium ion concentration in the cytoplasm of a neuron ________ when its voltage-gated sodium channels open.
A. increase
B. decrease
C. remains unchanged
D. decreases tenfold
answer
A increase
question
Depolarization of the neuron refers to __________.
A. a reduction in membrane potential
B. an increase in membrane potential
C. an increased negativity of the neuron interior
D. both b and c
answer
A. a reduction in membrane potential
question
During membrane repolarization, there is a decrease in the membrane permeability to which ion?
A. potassium
B. sodium
C. calcium
D. both potassium and sodium
answer
B. sodium
question
Neurons generally repolarizing once the membrane potential reaches approximately +30mV because:
A. voltage gated sodium activation gates close
B. voltage-gated potassium channels open up
C. voltage-gated sodium inactivation gates open up
D. voltage-gated calcium channel gates open
answer
B. voltage-gated potassium channels open up
question
In an organism, action potentials are propagated unidirectionally toward the axon ending because:
A. membranes become nonresponsive due to inactive sodium channels after action potential generation
B. action potentials are always propagated in an anterograde fashion regardless of conditions
C. action potentials cannot start anywhere except at the axon hillock
D. both a and b
answer
A. membranes become nonresponsive due to inactive sodium channels after action potential generation
question
Stronger stimuli are interpreted when the CNS receives ______ action potentials
A. higher magnitude
B. more frequent
C. lower magnitude
D. more infrequent
answer
B. more frequent
question
The nodes of Ranvier are found _________.
A. in the CNS only
B. on dendrites
C. on the neuroglia
D. on myelinated axons
answer
D. on myelinated axons
question
The location at which a neuron interacts with its target cell (another neuron or a muscle cell or other effector cells is called the _________.
A. synapse
B. junction
C. connection
D. axaxonic target
answer
A. synapse
question
The presynaptic neuron releases neurotransmitters in response to an influx of _______ ions.
A. sodium
B. potassium
C. calcium
D. sodium and potassium
answer
C. calcium
question
Which type of potential does not decay with distance?
A. Graded potential
B. Action potential
C. Generator potential
D. Both a and b
answer
B. Action potential
question
Neurotransmitters are important in functioning of ______ synapses.
A. chemical
B. electrical
C. gap
D. converging
answer
A. chemical
question
You would expect a neuron that depolarizes to -75 mV would:
A. return to resting membrane potential without generating an action potential.
B. fire a much more intense action potential with a peak of +100 mV.
C. fire a much less intense action potential with a peak of +15 mV.
D.hyperpolarize.
answer
A. return to resting membrane potential without generating an action potential.
question
The point at which the all-or-none principle of action potential generation is reached is termed the ________.
A. peak
B. depolarization point
C. threshold
D. point of no return
answer
C. threshold
question
During the events involved in information transfer across a chemical synapse, which of the following steps would be interrupted by exposing a neuron to a calcium channel blocker?
A. Neurotransmitter exocytosis from the presynaptic neuron
B. Depolarization of the presynaptic neuron
C. Binding of neurotransmitters to the postsynaptic membrane
D.Depolarization of the postsynaptic membrane
answer
A. Neurotransmitter exocytosis from the presynaptic neuron
question
During the relative refractory period:
A. no action potentials can be generated.
B. the threshold is substantially elevated.
C. exceptionally strong stimuli could trigger action potentials.
D. both b and c apply.
answer
D. both b and c apply.
question
Generally speaking, opening chloride channels in the postsynaptic membrane will result in an _______.
A. excitatory postsynaptic potential
B. excitatory presynaptic potential
C. inhibitory postsynaptic potential
D. inhibitory presynaptic potential
answer
C. inhibitory postsynaptic potential
question
__________ has occurred when a neuron is stimulated by more than one terminal.
a. Temporal summation
b. Spatial summation
c. Synaptic delay
d. Synaptic potentiation
answer
b. Spatial summation
question
Generation of an action potential can be inhibited by all of the following except:
a. IPSPs.
b. presynaptic inhibition.
c. depolarization.
d. hyperpolarization.
answer
c. depolarization.
question
As a general rule of thumb, the greater the potential difference in charge between two points, the __________ the voltage.
A. Higher
B. Lower
C. Less difference in
D. More even
answer
A. Higher
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