Chapter 11 EXAM Physiology
Chapter Quiz #25 Which of the following is characteristic of an action potential? A. voltage-gated ion channels B. travels a short distance C. absent of positive feedback D. occurs in the dendrites and cell body
A. voltage-gated ion channels
What neurotransmitters bring resting post-synaptic neurons toward their threshold?
Acetylcholine and Glutamate
What is the 1st step of passing signals from neuron to neuron?
Action potential reaches axon terminal
Check Your Understanding #15: Which is bigger, a graded potential or an action potential? Which travels farther? Which initiates the other?
Action potentials are larger than graded potentials and travel farther. Graded potentials generally initiate action potentials.
Chapter Quiz #9 Which of the following electrical events occurs when a certain threshold is reached? A. resting membrane potential B. action potential C. EPSP D. IPSP
B. action potential
Chapter Quiz #14 The CNS can discriminate between strong and weak stimuli as strong stimuli __________. A. hyperpolarize the neuron B. increase the frequency of action potentials shift threshold C. increase the amplitude of action potentials
B. increase the frequency of action potentials shift threshold
Chapter Practice Test #14 Which of the following membrane ion channels open and close in response to changes in the membrane potential? A. nongated channels B. voltage-gated channels C. mechanically gated channels D. chemically gated channels
B. voltage-gated channels
What is the 5th step of passing signals from neuron to neuron?
Binding of neurotransmitter causes post-synaptic ion channels to open
Chapter Quiz #11 In a neuron, a membrane potential of -90 mV is considered __________. A. depolarized B. a graded potential C. a normal resting potential D. Hyperpolarized
D. Hyperpolarized
Chapter Quiz #10 Which of the following factors is associated with increased conduction velocity in an axon? A. small diameter B. the absence of the myelin sheath C. increased number of dendrites D. large diameter E. presence of collaterals
D. large diameter
Check Your Understanding #4: Which two types of neuroglia form insulating coverings called myelin sheaths?
Oligodendrocytes and Schwann cells.
What stimulates ligand-gated channels to open?
binding of ligands (chemicals; e.g. neurotransmitters)
Lidocaine is an anaesthetic. How does it block sensory signals via an effect on Na+ channels?
blocks voltage-gated Na+ channels, preventing action potentials from sweeping down the axons.
What stimulates voltage-gated channels to open?
the cell membrane reaching a certain voltage (threshold)
Review Question #19 Describe the events that must occur to generate an AP. Relate the sequence of changes in permeability to changes in the ion channels, and explain why the AP is an all-or-none phenomenon.
1) an increase in sodium permeability and reversal of the membrane potential (2) a decrease in sodium permeability (3) an increase in potassium permeability and repolarization. The all-or-none phenomenon means that the local depolarizing current must reach a critical threshold point before membrane channels will respond, and when a response occurs, it will lead to the conduction of an action potential along the entire length of the axon.
Check Your Understanding #9: Which part of the neuron is its fiber? How do nerve fibers differ from the fibers of connective tissue (see Chapter 4) and the fibers in muscle (see Chapter 9)?
A nerve fiber is a long axon, an extension of the cell. In connective tissue, fibers are extracellular proteins that provide support. In muscle tissue, a muscle fiber is a muscle cell.
Check Your Understanding #16: An action potential does not get smaller as it propagates along an axon. Why not?
An action potential is regenerated anew at each membrane patch.
Acetylcholine opens Na+ channels. does this lead to an EPSP or IPSP?
EPSP
Glutamine opens Na+ channels. does this lead to an EPSP or IPSP?
EPSP
In a Na+ channel, if Na+ enters the cell that qualifies as an _____.
EPSP
What is the 4th step of passing signals from neuron to neuron?
Neurotransmitter diffuses across synaptic cleft, binds to receptors in membrane of post-synaptic cell.
What is the 6th step of passing signals from neuron to neuron?
Neurotransmitter is disposed of.
Chapter Practice Test #15 True or False: An action potential is a phenomenon that either happens completely or doesn't happen at all.
True
What is a chemical gradient (for all substances)?
Substances diffuse from areas of higher concentration to areas of lower concentration
Check Your Understanding #23: What is the difference between temporal summation and spatial summation?
Temporal summation is summation in time of graded potentials occurring in quick succession at the postsynaptic membrane. It can result from EPSPs arising from just one synapse. Spatial summation is summation in space—a postsynaptic neuron is stimulated by a large number of terminals at the same time.
Chapter Practice Test #7 True or False: Dendrites and axons are both armlike processes that extend from neuron cell bodies.
True
Check Your Understanding #10: For an open channel, what factors determine in which direction ions will move through that channel?
The electrochemical gradient determines the direction in which ions flow through an open membrane channel.
What determines whether ions enter the cell or exit the cell?
The electrochemical gradient for that ion
What is "threshold" for a voltage-gated channel?
The membrane potential (voltage) at which the channel will open
How does the dumping of neurotransmitters into the synaptic cleft affect the post-synaptic neuron?
The neurotransmitter will bind to post-synaptic receptors, directly or indirectly causing some ion channels to open and thus changing the post-synaptic membrane potential.
What is an electrochemical gradient (for ions)?
The overall driving force for an ion, based on both its chemical and electrical gradients (which may reinforce each other OR may oppose each other).
Neurons A, B, and C all synapse onto post-synaptic neuron P. However, during a certain period of time, you only observe A firing. Each time that A fires, P fires soon after. Is this spatial summation, temporal summation, both, or neither?
This is neither. If a single action potential from A is enough to get P to fire, then no summation is needed.
What is the 2nd step of passing signals from neuron to neuron?
Voltage-gated calcium channels open, calcium enters.
Check Your Understanding #20: Draw a chemical synapse, showing the locations of voltage-gated and chemically gated ion channels. What causes each to open?
Voltage-gated ion channels open when an action potential reaches the axon terminal. Chemically gated ion channels open when neurotransmitter binds to the receptor protein.
For the question "Is this stimulus strong enough for the brain to pay attention to?," do excitatory neurons need to fire in large quantities?
Yes. One or two neurons firing does not open enough ion channels to reach threshold, so more are needed to fire an AP.
_____ spread causes the opening of additional ion channels.
active spread
only _____ spread regenerates the depolarization, so that it does not decay with distance.
active spread
In which parts of neurons (dendrites, soma, and/or axon)are ligand-gated channels found?
dendrites and soma
Why do serotonin-specific reuptake inhibitors (SSRIs) intensify stimulation of post-synaptic neurons?
inhibit reuptake of serotonin (a neurotransmitter).
Why does cocaine intensify stimulation of post-synaptic neurons that receive the neurotransmitter dopamine?
inhibits reuptake of dopamine (a neurotransmitter) into pre-synaptic neurons, enhancing dopamine's effect on the postsynaptic neurons.
relative to the outside of the cell membrane, the inside is...
more negative
What does "repolarization" mean?
moving back toward the resting voltage.
What is the membrane potential of a typical "resting" neuron?
negative-70 mV, i.e., 70 millivolts below zero.
Cl- is electrically attracted (into / out of) of the cell.
out of the cell
At a particular moment in time, a neuron receives neurotransmitters from various pre-synaptic neurons that cause the post-synaptic potentials (PSPs) shown below at the locations shown below. Do you think the axon will fire an action potential as a result of these PSPs? Explain your reasoning.
(A) PSPs sum together at any given moment in time, so if three different inputs lead to depolarizations of different dendrites, those local EPSPs will sum together as they spread to the axon hillock. (B) However, these EPSPs will also decay as they spread, and be smaller by the time they reach the axon hillock. (C) Threshold at the axon hillock is normally about 10 to 15 mV above resting potential, so with +11 mV worth of depolarizations spreading from the dendrites, what gets to the axon hillock will be less than +11 mV, and probably not enough to reach threshold.
Review Question #20 (a) Explain the difference between an EPSP and an IPSP. (b) What specifically determines whether an EPSP or IPSP will be generated at the postsynaptic membrane?
(a) An EPSP is an excitatory (depolarizing) postsynaptic potential that increases the chance of an action potential. An IPSP is an inhibitory (hyperpolarizing) postsynaptic potential that decreases the chance of an action potential. (b) EPSPs and IPSPs are determined by the type and amount of neurotransmitter that binds at the postsynaptic neuron and the specific receptor subtype to which it binds.
Review Question #15 The velocity of nerve impulse conduction is greatest in (a) heavily myelinated large-diameter fibers (b) myelinated, small-diameter fibers (c) nonmyelinated, small-diameter fibers (d) nonmyelinated, large-diameter fibers.
(a) heavily myelinated large-diameter fibers
Review Question #9 An IPSP is inhibitory because (a) it hyperpolarizes the postsynaptic membrane (b) it reduces the amount of neurotransmitter released by the presynaptic terminal (c) it prevents calcium ion entry into the presynaptic terminal (d) it changes the threshold of the neuron.
(a) it hyperpolarizes the postsynaptic membrane
Review Question #1 Which of the following structures is not part of the central nervous system? (a) the brain (b) a nerve (c) the spinal cord (d) a tract.
(b) a nerve
Review Question #4 Chemical synapses are characterized by all of the following except (a) the release of neurotransmitter by the presynaptic membranes (b) postsynaptic membranes bearing receptors that bind neurotransmitter (c) ions flowing through protein channels from the presynaptic to the postsynaptic neuron (d) a fluid-filled gap separating the neurons.
(c) ions flowing through protein channels from the presynaptic to the postsynaptic neuron
Chapter Quiz #12 During which phase of an action potential are voltage-gated K+ channels open, while voltage-gated Na+ channels are closed? A. threshold B. repolarization C. depolarization D. resting state
B. repolarization
Why do inhibitory neurons fire action potentials just like excitatory neurons?
Both the excitatory and inhibitory neurons reach a threshold at which voltage-gated Na+ channels open, etc. The only difference between them is which neurotransmitter is released
Chapter Quiz #8 Which of the following events occurs at an electrical synapse? A. Neurotransmitters diffuse across the synaptic cleft. B. Neurotransmitters bind to the postsynaptic receptors. C. Ions flow directly from one neuron to the next. D. A neurotransmitter is released by exocytosis. E. Calcium channels open in the presynaptic region.
C. Ions flow directly from one neuron to the next.
Chapter Quiz #16 Which of the following statements concerning inhibitory synapses (IPSPs) is correct? A. Channels allow both sodium and potassium ions to diffuse simultaneously through the membrane. B. The postsynaptic membrane becomes less permeable to sodium. C. The postsynaptic membrane becomes more permeable to potassium and chloride. D. The permeability of the postsynaptic membrane to sodium, potassium, and chloride is not changed. E. The postsynaptic membrane becomes less permeable to potassium.
C. The postsynaptic membrane becomes more permeable to potassium and chloride.
Chapter Practice Test #20 Which type of ion channel opens when a chemical binds to it? A. leakage channel B. mechanically gated channel C. chemically gated (ligand-gated) channel D. voltage-gated channel
C. chemically gated (ligand-gated) channel
Chapter Practice Test #8 Which of the following are the main receptive or input regions found in neurons? A. axons B. ganglia C. dendrites D. Neurofibrils
C. dendrites
Chapter Practice Test #22 Which part of the action potential occurs when the voltage-gated Na+ channels are inactivating and voltage-gated K+ channels open? A. Depolarization B. Resting state C. repolarization D. hyperpolarization
C. repolarization
Chapter Quiz #7 Which of the following characteristics is NOT associated with a myelinated nerve fiber? A. formation by Schwann cells in the peripheral nervous system B. rapid conduction of nerve impulses C. slow conduction of nerve impulses D. formation by oligodendrocytes in the central nervous system E. the presence of nodes of Ranvier
C. slow conduction of nerve impulses
Chapter Practice Test #9 Which of the following is NOT a function of the myelin sheath? A. to protect nerve fibers B. to electrically insulate nerve fibers C. to recapture and recycle released neurotransmitters D. to increase the speed of transmission of nerve impulses
C. to recapture and recycle released neurotransmitters
What is the 3rd step of passing signals from neuron to neuron?
Calcium binds to synaptic vesicles, causing them to release neurotransmitter by exocytosis
What is an electrical gradient (for ions)?
Charges repel, opposite charges attract
Review Question #21 Since at any moment a neuron is likely to have thousands of neurons releasing neurotransmitters at its surface, how is neuronal activity (to fire or not to fire) determined?
Each neuron's axon hillock keeps a "running account" of all graded potentials it receives via temporal and spatial summation. The net amount of depolarization determines whether or not threshold for an action potential has been reached. (pp. 419-420)
Additional practice: If given a post-synaptic potential, indicate which ion flow(s) through which ion channels could have given rise to it. • Example: A PSP of negative-6 millivolts, relative to baseline.
For this scenario, the membrane potential is hyperpolarizing, so this is an IPSP. This could be due to an influx of chloride (Cl-) or an outflow of potassium (K+).
What neurotransmitters do not bring resting post-synaptic neurons toward their threshold?
GABA and Glycine
Glycine opens Cl- channels. does this lead to an EPSP or IPSP?
IPSP
In a Cl- channel, if Cl-enters the cell that qualifies as an _____.
IPSP
In a K+ channel, if K+ exits the cell that qualifies as an _____.
IPSP
GABA opens K+ or CL- channels. does this lead to an EPSP or IPSP?
IPSP
Review Question #12 Since all APs generated by a given nerve fiber have the same magnitude, how does the CNS "know" whether a stimulus is strong or weak?
The CNS interprets a stimulus as strong when the frequency, or rate, of action potentials arriving at the CNS is high. Conversely, a low frequency of action potentials indicates a weaker stimulus.
For the question "Which of these 2 stimuli is stronger?," explain why a post-synaptic neuron Z might fire if and only if pre-synaptic neuron A is more active than B.
Threshold is only reached if A (excitatory) is firing significantly more often than B (inhibitory), and thus gets Z to threshold despite B's action pulling Z away from threshold.
In which parts of neurons (dendrites, soma, and/or axon) are voltage-gated channels found?
along the axon
What is meant by the term "membrane potential"?
difference in charge between outside of membrane and inside of membrane
Cl- is chemically attracted (into / out of) the cell.
into the cell
K+ is electrically attracted (into / out of) of the cell.
into the cell
Na+ is chemically attracted (into / out of) the cell.
into the cell
Na+ is electrically attracted (in/out) of the cell.
into the cell
The overall electrochemical gradient of Cl- attracts sodium ions (into / out of) the cell.
into the cell
The overall electrochemical gradient of Na+ attracts sodium ions (into / out of) the cell.
into the cell
K+ is chemically attracted (into / out of) the cell.
out of the cell
The overall electrochemical gradient of K+ attracts sodium ions (into / out of) the cell.
out of the cell
____ spread does not cause the opening of additional ion channels.
passive spread
For a cell membrane, what does "depolarization" mean?
the membrane becoming less negative and reaching at or above -55 mV