Chapter 10.6: Changed in Stimulus Intensity/Frequency

Twitch

• brief contraction of single stimulus

• minimal voltage that triggers is threshold

Period of twitch: latent

• time after stim but before contraction begins

• no change in tension

Period of twitch: Contraction

• tension is increasing

• begins as power strokes pull thin filaments

Periods of twitch: Relaxation

• tension decreasing to baseline

• beings with release of crossbridge

• generally last longer than contraction period

Recruitment (multiple motor unit summation)

• voltage increases, more units recruit to contract

  • explains varying degrees of force, picking up pencil versus suitcase

Wave summation (temporal summation)

• frequency 20 per sec, relaxation not complete between twitches, contractile forces add up produce higher tension

Incomplete tetany vs tetany

• increase past 20 per sec = incomplete tetany

  • twitches partially fuse

• increased further (40-50/sec) = tetany

  • tension is smooth line withou relaxation

• high frequency stimuli lead to fatigue