U3 Lecture 23 Flashcards
- List the 3 phases of a muscle twitch - Compare and contrast the characteristics of a muscle twitch and tetanic contraction. Describe the development of tetanus in terms of temporal summation - Define a motor unit and and discuss it in the context of spatial summation - describe the 'size principle' in the context of development of increased tension during a voluntary muscle contraction - Describe isometric and isotonic contraction - Describe the strategies used to increase force in the mu
Define muscle twitch
Contraction arising from a single electrical stimulus (like AP)
What are the 3 periods of muscle twitches?
Latent, Contraction, and Relaxation
Latent Period
- 2 msec or less
- Action potential sweeps over the sarcolemma
- Ca2+ is released from the SR
- No change in tension
Contraction Period
- 10-100 msec
- Ca2+ binds to troponin
- Myosin-binding site on actin are exposed
- crossbridge cycle begins and continues
- Peak tension develops
Relaxation Period
- 10 - 100 msec
- Ca2+ transported back into SR
- Myosin-binding sites are covered by tropomyosin
- Crissbridge cycle ends (Myosin can no longer to sites on actin)
- Tension decreases
What is unique about twitches?
Twitches vary for each muscle (fast - slow)
- fast : eye
- medium : gastroc.
- slow : soleus
Define Tetanus
‘summation’ over time (temporal summation) of individual twitches
Tetanus is a mechanism for what?
Increasing tension
Define motor unit
A motor neuron and all the muscle fibers (cells) it innervates
Do muscles have many or one motor unit?
Many
Define spatial summation
Recruiting/ increasing numbers of motor units -> tension is increased
What size is the first motor units recruited?
Small (innervate few fibers)
Slow = ?
Slow, oxidative
Intermediate = ?
Fast, oxidative-glycolytic (fatigue resistant)
Fast = ?
Fast, glycolytic (fatigable)
