What part of the nervous system performs information processing and integration?
central nervous system
Which of the following types of neurons carries impulses away from the CNS?
motor
Which of the following does not factor into the rate of impulse propagation?
The number of axon collaterals extending from a truncated axon.
Which of the following is not true of an electrical synapse?
They are specialized for release and reception of chemical neurotransmitters.
Which part of the neuron is responsible for generating a nerve impulse?
axon
Which of the following PNS neuroglia help to form myelin sheaths around larger nerve fibers in the PNS?
Schwann cells
Which of the following is the conducting region of the neuron?
Axon
Which of the following is not a functional classification of neurons?
Extraneurons
Which neuroglia are the most abundant and versatile of the glial cells?
astrocytes
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).
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)
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 __________.
saltatory conduction
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.
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.
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.
What type of conduction takes place in unmyelinated axons?
Continuous conduction
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
Where do most action potentials originate?
Initial segment
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.
Where in the neuron is an action potential initially generated?
axon hillock
The depolarization phase of an action potential results from the opening of which channels?
voltage-gated Na+ channels
The repolarization phase of an action potential results from __________.
the opening of voltage-gated K+ channels
Hyperpolarization results from __________.
slow closing of voltage-gated K+ channels
What is the magnitude (amplitude) of an action potential?
100 mV
A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell?
a neuron
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?
exocytosis
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
In a synapse, neurotransmitters are stored in vesicles located in the __________.
presynaptic neuron
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?
acetylcholine
Which pattern or neural processing works in a predictable, all-or-nothing manner, where reflexes are rapid, automatic responses to stimuli in which a particular stimulus always causes the same response?
Serial processing
Which neurotransmitter(s) is/are the body's natural pain killer?
endorphins
What component of the reflex arc determines the response to a stimulus?
integration center
The sodium-potassium pump ejects two Na from the cell and then transports three K back into the cell in order to stabilize the resting membrane potential.
False
Unmyelinated fibers conduct impulses faster than myelinated fibers.
False
Neurons and nerve cells are different names for the same thing.
True
Which neuron circuit pattern is involved in the control of rhythmic activities such as breathing?
reverberating circuit
Which criteria is used to functionally classify neurons?
The direction in which the nerve impulse travels relative to the central nervous system.
Which membrane potential results in depolarization without a nerve impulse being generated?
excitatory postsynaptic potential