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The fundamental excitable cell in the nervous system is the _____. a) axon |
d) neuron A neuron is the fundamental cell type of the nervous system. This excitable cell utilizes electrochemical mechanisms to transmit signals from one location in the body to another. |
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The knee-jerk reflex has sensory neurons arising in the _____, interneurons in the _____, and efferent neurons that stimulate contraction in the _____. a) autonomic nervous system … peripheral nervous system … smooth muscles in the leg |
e) quadriceps muscle … spinal cord … hamstring muscle This spinal reflex helps a physician assess function of the spinal cord and muscles. |
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The cerebrospinal fluid is _____. a) secreted by the hypothalamus |
c) a filtrate of the blood |
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A neuron’s nucleus is located in its _____. a) cell body |
a) cell body The cell body is the region of a neuron where the nucleus is found. |
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A nerve impulse moves toward a neuron’s cell body along _____. a) dendrites |
a) dendrites Dendrites conduct an impulse from a synapse toward the cell body. |
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A nerve impulse moves away from a neuron’s cell body along _____. a) dendrites |
d) axons Axons conduct a nerve impulse away from the cell body. |
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An impulse relayed along a myelinated axon "jumps" from _____ to _____. a) oligodendrocyte … Schwann cell |
c) node of Ranvier … node of Ranvier In myelinated neurons the impulse jumps from node of Ranvier to node of Ranvier. |
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Axons insulated by a(n) _____ are able to conduct impulses faster that those not so insulated. a) node of Ranvier |
c) myelin sheath Myelin sheaths, formed when Schwann cells wrap around an axon, allow such neurons to conduct impulses more rapidly than unmyelinated axons. |
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What type of cell makes up the myelin sheath of a motor neuron? a) astrocytes |
e) Schwann cells Myelin sheaths are formed when Schwann cells wrap around the axons of motor neurons. |
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What part of a neuron relays signals from one neuron to another neuron or to an effector? a) dendrite |
c) synaptic terminal Synaptic terminals contain neurotransmitter molecules that relay the nerve impulse across a synapse. |
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The "information receiving" section of a neuron is its _____. a) glia |
c) dendrites The dendrites have receptor proteins that receive information by binding chemical messages called neurotransmitters. |
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Most of the neurons in the human brain are _____. a) motor neurons |
c) interneurons |
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In a simple synapse, neurotransmitter chemicals are released by _____. a) the presynaptic membrane |
a) the presynaptic membrane |
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Which term describes the difference in electrical charge across a membrane? a) Membrane potential. |
a) Membrane potential. Membrane potential is the difference in electrical charge across a membrane. |
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Resting neurons are most permeable to which of the following ions? a) Na+. |
d) K+. Resting neurons are most permeable to K+ ions. |
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True or false? The potential energy of a membrane potential comes solely from the difference in electrical charge across the membrane. a) True |
b) False The potential energy of a membrane potential comes both from the difference in electrical charge and from the concentration gradient of ions across a membrane. |
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Which channel is mainly responsible for the resting potential of a neuron? a) Potassium leak channel. |
a) Potassium leak channel. K+ ions flow along their concentration gradient to maintain the resting potential of a neuron. |
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Which term describes an electrical signal generated by neurons? a) Resting potential. |
d) Action potential. An action potential is a rapid electrical signal generated by neurons. |
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Which channel maintains the concentration gradients of ions across a neuronal membrane? a) The sodium-potassium pump moving Na+ ions out and K+ ions in. |
a) The sodium-potassium pump moving Na+ ions out and K+ ions in. This channel maintains the ion concentration gradients across a neuronal membrane. |
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What behavior is observed if the voltage across a neuronal membrane is set to -20 mV? a) The sodium channel opens, and Na+ ions flow out. |
c) The sodium channel opens, and Na+ ions flow in. Sodium ions flow into the cell when the membrane potential is between -20 mV and 30 mV. |
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The operation of the sodium-potassium "pump" moves _____. a) sodium and potassium ions into the cell |
d) sodium ions out of the cell and potassium ions into the cell |
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The membrane potential in which there is no net movement of the ion across the membrane is called the _____. a) equilibrium potential |
a) equilibrium potential |
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Two fundamental concepts about the ion channels of a "resting" neuron are that the channels _____. a) are always closed, but ions move closer to the channels during excitation |
b) open and close depending on stimuli, and are specific as to which ion can traverse them |
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Which structure is not part of a neuron? a) Axons. |
c) Myelin sheath. The myelin sheath is the layer of Schwann cells wrapped around a neuron. |
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Which of the following statements about action potentials in a given neuron is false? a) They are identical in magnitude. |
c) They are propagated down the length of the dendrite. They are propagated down the length of the axon. |
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True or false? Action potentials travel in only one direction down an axon because potassium channels in the neuron are refractory and cannot be activated for a short time after they open and close. a) True |
b) False Action potentials travel in only one direction down an axon because sodium channels in the neuron are refractory. |
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Which event triggers the creation of an action potential? a) The sodium—potassium pump shuttles ions across the membrane. |
b) The membrane depolarizes above a certain threshold potential. Influx of Na+ ions into the neuron can lead to membrane depolarization above the threshold potential; this event triggers the creation of an action potential. |
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Which of the following terms describes how a neuronal membrane’s potential is altered in the presence of inhibitory signals? a) Hyperpolarization. |
a) Hyperpolarization Inhibitory signals hyperpolarize the membrane and make the membrane potential even more negative than normal. |
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Where in the neuron do action potentials begin? a) Dendrite. |
c) Axon hillcock. The axon hillock is the region where voltage-gated channels begin in a neuron, near the cell body. |
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How is an action potential propagated down an axon after voltage-gated sodium channels open in a region of the neuron’s membrane? a) Potassium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated potassium channels farther down the axon. |
c) Sodium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated sodium channels farther down the axon. The entry of sodium ions into the neuron and their diffusion to adjacent areas of the membrane causes those portions of the membrane to become depolarized and results in the opening of voltage-gated sodium channels farther down the axon, which release potassium ions to the outside, returning the charge to its previous state. |
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A neuron has a resting potential of about _____ millivolts. a) +50 |
d) -70 This is the resting potential, the charge difference found across the plasma membrane of a "resting" neuron. |
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An action potential moves along a(n) _____. a) myelin sheath |
b) axon An axon is the only portion of a neuron capable of generating an action potential. |
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At rest, which of these plays a role in establishing the charge differential across a neuron’s plasma membrane? a) the sodium-potassium pump moving sodium ions into the neuron and potassium ions out of the neuron |
d) the sodium-potassium pump moving sodium ions out of the neuron and potassium ions into the neuron The sodium-potassium pump moves more sodium ions out of the cell than potassium ions into the cell; this net loss of positive ions establishes a charge differential across the plasma membrane. |
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The transmission of a nerve impulse first triggers the _____. a) action of the sodium-potassium pump |
b) opening of voltage-gated sodium channels and the diffusion of sodium ions into the neuron This is the first of the events listed here. As a result of the inward flux of sodium ions, that region of the neuron depolarizes. |
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A stimulus has opened the voltage-gated sodium channels in an area of a neuron’s plasma membrane. As a result, _____ rushes into the neuron and diffuses to adjacent areas; this in turn results in the _____ in the adjacent areas. a) potassium … opening of voltage-gated potassium channels |
c) sodium … opening of voltage-gated sodium channels This describes part of the process by which an action potential travels along an axon. |
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A graded hyperpolarization of a membrane can be induced by _____. a) increasing its membrane’s permeability to Na+ |
c) increasing its membrane’s permeability to K+ |
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After the depolarization phase of an action potential, the resting potential is restored by _____. a) the opening of voltage-gated potassium channels and the closing of sodium channels |
a) the opening of voltage-gated potassium channels and the closing of sodium channels |
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The "undershoot" phase of after-hyperpolarization is due to _____. a) rapid opening of voltage-gated calcium channels |
b) sustained opening of voltage-gated potassium channels |
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Why are action potentials usually conducted in one direction? a) The nodes of Ranvier conduct potentials in one direction. |
c) The brief refractory period prevents reopening of voltage-gated Na+ channels. |
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Why do Na+ ions enter the cell when voltage-gated Na+ channels are opened in neurons? a) because the Na+ concentration is much lower outside the cell than it is inside |
b) because the Na+ concentration is much higher outside the cell than it is inside, and the Na+ ions are attracted to the negatively charged interior |
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Which of the following will increase the speed of an action potential moving down an axon? |
I) Action potentials move faster in larger diameter axons. III) Action potentials move faster in myelinated axons. |
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Which of these causes the release of neurotransmitter molecules? a) the receipt of a signal from the postsynaptic neuron |
d) an action potential reaching the end of the axon When an action potential reaches the end of an axon, vesicles fuse with the plasma membrane and release neurotransmitter into the synaptic cleft. |
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The space between an axon of one neuron and the dendrite of another neuron is called a(n) _____. a) synaptic cleft |
a) synaptic cleft "Synaptic cleft" is the name given to the space between two neurons that meet at a synapse. |
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Neurons store neurotransmitter molecules in vesicles located within _____. a) the cell body |
e) synaptic terminals Vesicles within synaptic terminals contain neurotransmitter that may be released into the synaptic cleft. |
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A nerve poison that blocks acetylcholine receptors on dendrites would _____. a) cause continued stimulation of the postsynaptic membrane |
c) reduce the binding of acetylcholine to its receptors on the postsynpatic membrane The binding of neurotransmitter molecules to their specific receptors on the postsynaptic membrane opens ion channels, which completes the transmission of the impulse to the receiving cell. A nerve poison that blocked the acetylcholine receptors would prevent reception of the signal. |
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The following steps refer to various stages in transmission at a chemical synapse. |
3. An action potential depolarizes the membrane of the presynaptic axon terminal. 2. Calcium ions rush into neuron’s cytoplasm. 5. The synaptic vesicles release neurotransmitter into the synaptic cleft. 1. Neurotransmitter binds with receptors associated with the postsynaptic membrane. 4. The ligand-gated ion channels open. |
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When two excitatory postsynaptic potentials (EPSPs) occur at a single synapse so rapidly in succession that the postsynaptic neuron’s membrane potential has not returned to the resting potential before the second EPSP arrives, the EPSPs add together producing _____. a) temporal summation |
a) temporal summation |
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Which of the following is a direct result of depolarizing the presynaptic membrane of an axon terminal? a) Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft. |
d) Voltage-gated calcium channels in the membrane open. |
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Suppose a particular neurotransmitter causes an IPSP in postsynaptic cell X and an EPSP in postsynaptic cell Y. A likely explanation is that __________. a) cells X and Y express different receptor molecules for this particular neurotransmitter |
a) cells X and Y express different receptor molecules for this particular neurotransmitter |
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The plasma membrane of a neuron has voltage-gated sodium and potassium channels. What is the effect of membrane depolarization on these channels? a) Membrane depolarization first opens sodium channels and then opens potassium channels. |
a) Membrane depolarization first opens sodium channels and then opens potassium channels. Membrane depolarization opens both types of channels, but they respond independently and sequentially. Sodium channels open first, initiating the action potential. As the action potential proceeds, the sodium channels become inactivated and remain inactivated until after the membrane returns to the resting potential and the channels close. Potassium channels open more slowly than sodium channels but remain open and functional throughout the action potential. Read about the generation of action potentials. |
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One of the fundamental processes by which memories are stored and learning takes place _____. a) results in an increase in the diameter of axons |
c) involves two types of glutamate receptors |
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