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Threshold for excitation
Each type of nerve has it' own thershold for exictation
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Define Excitation
the events leading to the generation of an action potential
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Define Conduction
the transmission or propagation of the action potential away from the site of stimulation
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Action Potential
- adequate stimulation of nerve axon or muscle cell cuase an abrupt change in the resting potential which leads to development of an action potential
- Deffernt kinds of stimuli can excite a nerve: chemical, electrical, thermal, mechanical
- Mechanism of excitation is always membrane depolarization
- ALL OR NONE
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Absolute Refractory Period
- Drief period in which the nerve is completely unexcitable to a second stimulus regardless of the intesity
- Same duration as the action potential
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Relative Refractory Period
- Immediately after the absolute refractory period
- Nerve excited by second stimulus: must be greater than it was at resting, nerve returns to normal resting state
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Strenght Duration Curve
- Effectiveness of an electrical stimulus depends on the intensity, duration and speed of rise time.
- Shorter Duration = increased intensity required for excitation
- Sensory, motor, pain, denerated
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Define Rheobase
- minimus intesity required to elicit a minimal visible contraction
- 100-300 msec duration used
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Define Chronaxie
duration required for a stimulus with 2x the rheobase intensity to elicit a minimal visible contraction
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Concepts from the strength duration curve
- Shorter duration = increased intensity
- Stimuli whith very short duration will not depolarize except with very high intensity
- There is a level of inensity where therte is no action potential generated at any duration
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A fiber
- Largest: conduct the afters
- Both motor and sensory
- Subdivided into alpha, beta, gamma, delta
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Larger Nerve Properties
- More Rapid conduction velocity
- lower threshold of excitability to peripherally applied electrial stimulus
- Shorter duration of excitatory response
- shorter refractory period
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B Fibers
- Smaller
- Slower
- autonomic in function
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C Fibers
- Smallest
- Slowest
- foudn in cutaneous and viseral nerves
- Associated with pain information, reflex responses and autonomic function
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Twitcha nd Tetany
- low frequency 1-2 stim/sec procduce a single response - twich contraction complete relaxation
- Increase frquencsy 15stim/sec Sp's summate and have unfues tetany can't fully relax
- Frquency greater than 30stim/sec is tetany
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