Cell Response to Electricity

  1. Threshold for excitation
    Each type of nerve has it' own thershold for exictation
  2. Define Excitation
    the events leading to the generation of an action potential
  3. Define Conduction
    the transmission or propagation of the action potential away from the site of stimulation
  4. 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
  5. 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
  6. 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
  7. 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
  8. Define Rheobase
    • minimus intesity required to elicit a minimal visible contraction
    • 100-300 msec duration used
  9. Define Chronaxie
    duration required for a stimulus with 2x the rheobase intensity to elicit a minimal visible contraction
  10. 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
  11. A fiber
    • Largest: conduct the afters
    • Both motor and sensory
    • Subdivided into alpha, beta, gamma, delta
  12. Larger Nerve Properties
    • More Rapid conduction velocity
    • lower threshold of excitability to peripherally applied electrial stimulus
    • Shorter duration of excitatory response
    • shorter refractory period
  13. B Fibers
    • Smaller
    • Slower
    • autonomic in function
  14. C Fibers
    • Smallest
    • Slowest
    • foudn in cutaneous and viseral nerves
    • Associated with pain information, reflex responses and autonomic function
  15. 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
Card Set
Cell Response to Electricity