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Cards In This Set
| Front | Back |
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Multipolar neurons
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3 or more processes; one axon the rest dendrites.
most common, 99%, CNS sensory input and motor output |
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Bipolar neurons
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2 processes; one axon, and a dendrite, extend from opposite ends of the cell body.
rare, special sense organs; retina of the eye, olfactory mucosa (never myelinated) |
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Unipolar neurons
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Single short process that emerges from the cell body, divides T-like into proximal and distal branches.
ganglia in the PNS, sensory neurons |
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Peripheral and central processes (neuron)
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Peripheral = distal, sensory receptor
central = enters the CNS unipolar neurons are reffered to as pseudounipolar neurons; originate as bipolar neurons |
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Absolute refractory period
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the neuron cannot respond to a second stimuli, no matter how strong.
period from the opening of the Na+ channel until the NA+ channel reset |
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Depolarization
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Cell interior becomes less negative due to an influx of sodium ions.
Na channels open, Na+ rushes in, driven by the ionic currents created by Na+ influx |
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Repolarization
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Potassium ions diffuse out of the neuron, due to membrane permeability.
rising phase of action potential is self limiting, Na+ channels begin to close, membrane permeability declines to resting levels |
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Action potential
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Nerve impulses transmited by axons
only cells with excitable membranes (neurons & muscle cells) brief reversal of membrane potential, potassium gates open after the peak |
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Relative refractory period
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Exceptionally strong stimulus can trigger a response.
interval following the absolute refractory period, repolarization is occuring |
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Temporal summation (wave)
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Numerous nerve impulses arriving at synapse at closely timed intervals exert a cumulative effect.
second contraction occurs before the muscle has completely relaxed |
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Spatial summation
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Stimulation of a postsynaptic neuron by many terminals at the same time.
EPSP's, enhance depolarization |
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Subthreshold stimulus
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Insufficient stimulus.
brief weak stimuli, produce subthreshold depolarization, not transmitted into nerve impulses |
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Threshold stimulus
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Stimulus below this intensity will result in no response in a neuron.
produce depolarizing currents that push the membrane potential toward and beyond threshold voltage |
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Trigger zone
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Where nerve impulse is generated.
junction of the axon hillcock and axon |
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Receptive region
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Receives stimuli, plasma membrane exhibits chemically gated ion channels.
dendrites, enormous surface area for receiving signals from other neurons |
