Propagation and Velocity of the Action Potential – Flashcards
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How is an action potential propagated along an axon?
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An influx of sodium ions from the current action potential depolarizes the adjacent area.
[the influx of sodium ions depolarizes adjacent areas, causing the membrane to reach threshold and cause an action potential. Thus, the action potential is regenerated at each new area.]
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Why does the action potential only move away from the cell body?
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The areas that have had the action potential are refractory to a new action potential.
[sodium channels are inactivated in the area that just had the action potential.]
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The velocity of the action potential is fastest in which of the following axons?
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a small myelinated axon
[ the myelination acts as insulation and the action potential is generated only at the nodes of Ranvier. Propagation along myelinated axons is known as saltatory conduction.]
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The central nervous system, which is composed of the brain and spinal cord, receives and processes information from both the external environment, known as __________ information and, the internal environment, which refers to __________ information.
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sensory : visceral
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What two divisions of the autonomic nervous system have opposite effects on the organs they innervate?
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parasympathetic and sympathetic
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What portion of the efferent branch of the nervous system communicates to glands and cardiac muscle?
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autonomic nervous system
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What portion of the efferent nervous system communicates with skeletal muscle?
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somatic nervous system
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What portion of the nervous system provides communication between peripheral organs and the brain and spinal cord?
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peripheral nervous system
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Voltage-gated calcium channels are localized to which part of the neuron?
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axon terminal
[Voltage-gated calcium channels are localized to the end of the axon where, when activated by an action potential, they initiate exocytosis of neurotransmitter.]
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On what portion of the neuron do action potentials propagate?
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axon
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In a neuron, where is the greatest concentration of voltage-gated sodium and voltage-gated potassium channels?
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axon hillock
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Which of the following best describes the function of the myelin sheath?
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reduce a membranes ion permeability
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The direction of change in membrane potential, in response to a stimulus that initiates a graded potential, is dependent upon
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the ion channels that are opened or closed.
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Which statement best describes how graded potentials determine whether an action potential will be generated or not?
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when an excitatory depolarization reaches threshold
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If the soma of a neuron became more permeable to potassium, which statement below best describes the graded potential that would be generated in the soma?
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Potassium would leave the cell, causing the membrane to hyperpolarize.
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Increased permeability to what ion is responsible for the relative refractory period?
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potassium (K+)
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The fact that the opening of some sodium channels can induce several other sodium channels to open describes the ________ property of these channels.
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regenerative
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Which of the following potentials has an all-or-none response?
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action potentials
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Which of the following potentials dissipate in size as the potential moves away from the site of initiation?
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graded potentials
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In myelinated nerve fibers, where do action potentials occur?
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nodes of Ranvier
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As an action potential is propagated away from the axon hillock, why does propagation continue in one direction?
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The region just behind the action potential is in the absolute refractory period
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What limits the maximum number of action potentials on an axon?
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the absolute refractory period
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How can action potentials relay information about the intensity of a stimulus, such as distinguishing between a loud and soft sound?
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due to the frequency of action potentials
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Toward the end of the relative refractory period, the continued decrease in stimulus intensity required to initiate an action potential is caused by
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decreased potassium permeability
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The all-or-none principle, associated with the action potential, states that
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once membrane potential reaches threshold, an action potential will be generated and that action potential will always be the same magnitude
