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42 Cards in this Set
- Front
- Back
Outside the central nervous system, clusters of neuron cell bodies are called
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ganglia
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Outside the central nervous system, axons travel together in bundles called
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nerves
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The resting membrane potential of a cell is produced by ion movements through
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Ion movements through leak channels, which are not gated (that is, they remain open continuously), produce the resting membrane potential of all cells, including neurons.
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In neurons that generate many action potentials, why don't the ion gradients across the neuron's cell membrane dissipate?
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Not many ions move across the membrane during an action potential. Those that do are pumped back across the membrane by the Na+/K+ ATPase. Leak channels remain open at all times, even during an action potential.
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The types of channels that can be found in excitable cells such as neurons include
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Nonexcitable cells only have leak channels. Excitable cells like neurons may have all three types of channels: ligand-gated, leak, and voltage-gated
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In contrast to almost all other cell types in the body, neurons
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Unlike other cell types, an excitable cell such as a neuron can alter its membrane potential by opening or closing gated ion channels, thereby altering membrane permeability.
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The resting membrane potential depends directly or indirectly on
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the Na+ and K+ ATPase, the ion permeability of the cell membrane, the concentration gradients of ions across the cell membrane
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Put the following events of the action potential in the correct order, starting with depolarization: a. Na+ permeability > K+ permeability b. K+ permeability > Na+ permeability c. Vm approaches EK+ d. Vm approaches ENa+ (Vm = membrane potential; EK+ = equilibrium potential for potassium; ENa+ = equilibrium potential for sodium)
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At the threshold for an action potential, Na+ permeability begins to exceed K+ permeability. At the peak of the action potential, the membrane potential approaches ENa+. During the downsweep phase, the permeability of the cell to K+ is greater than that for Na+, and increases until the membrane potential approaches EK+.
a,d,b,c |
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Refractory periods contribute to which of the following properties of action potentials?
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Once an action potential propagates in one direction, it cannot "go backwards" because the patch of membrane that the action potential just passed through will be in the refractory period. The length of the refractory period in a neuron also helps to determine how many action potentials can be initiated per unit time, i.e., action potential frequency. Also, refractory periods prevent the overlap of action potentials, so they cannot summate the way graded potentials can.
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Graded potentials and action potentials are similar in that
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Only action potentials show an all or none response to a stimulus. Graded potentials decrement over distance and change their amplitude depending on stimulus strength.
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Sensory neurons are also called ______ neurons because they transmit information toward the central nervous system
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Afferent neurons transmit information to the central nervous system; efferent neurons transmit information away from the central nervous system.
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dendrites
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input area; receives signals from other neurons
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soma (cell body)
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input area; main nutritional and metabolic area
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axon
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conductive region; generates an action potential
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The area where the axon emerges from the soma
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axon hillock
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the action potential is generated from the
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axon hillock
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what support cell forms the myelin sheath?
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shwann cells
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myelin is found around which part of the neuron?
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axon
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the tightly wound cell membrane around the axon forms the myelin sheath and acts as a
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conductor
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the most common central nervous system neuron is called a _________ neuron.
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sensory (afferent)
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neurons have _____ axon(s)
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only one
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axons are ____ branched
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frequently
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Dendrites have _____ branch(es)
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many
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Neurons that innervate smooth muscle, such as the lining of blood vessels or the GI tract, belong to the __________ nervous system.
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peripheral, autonomic
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Glial cells ________.
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constitute 90% of the cells in the nervous system
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Interneurons
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are located entirely within the CNS
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Schwann cells
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are located in the peripheral nervous system, are a type of glial cell
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Action potentials propagate down the axon
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like a row of falling dominoes, by current flow through the intra- and extracellular fluid around sequential areas of the axonal membrane, by current flow through electrotonic conduction
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The neurotoxin called tetrodotoxin, or TTX,
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blocks voltage-gated sodium channels
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at the resting membrane potential,
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sodium is leaking into the cell, potassium is leaking out of the cell
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If the Na+/K+ ATPase was turned off, the membrane potential would eventually become equal to _______.
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zero mV
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Graded potentials
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spread through electrotonic conduction, can summate, and can be depolarizing or hyperpolarizing
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In sodium channels at the resting membrane potential,
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the activation gate is closed and the inactivation gate is open
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The positive feedback loop during the depolarization phase of the action potential is "turned off" during repolarization because
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Na+ channels inactivate, K+ channels open
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The amplitude of the peak of the action potential depends on
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the relative sizes of the electrochemical gradients for Na+ and K+, the differences in Na+ and K+ permeability
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During the after-hyperpolarization phase of the action potential,
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potassium channels are closing
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A suprathreshold stimulus can
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inc the frequency of action potentials
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Effector organs
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are muscles, are glands, may be controlled by the somatic nervous system, may be controlled by the autonomic nervous system
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Action potentials
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propagate faster in larger diameter axons, cannot go backward over a previously depolarized patch of membrane, can propagate in only one direction
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In myelinated axons,
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action potentials propagate by electronic conduction, minimal current leaks across the membrane between nodes, currents must reach the next node before the membrane potential falls below threshold
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During an action potential, what changes significantly?
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the membrane potential
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Action potential conduction velocity is the slowest in
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small unmyelinated axons
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