muscles iv Flashcards
maximum tension depends on:
- rate of nerve impulse arrival
- amount of stretch before contraction
- nutrient and oxygen availability
- size of motor unit
How does load affect muscle contraction
A heavy load produces slower and shorter contractions
Muscle twitch
a mechanical event that’s the result of a single AP in one muscle fiber
3 parts of muscle twitch
- latent period = delay from stimulus onset to increased tension (includes EC coupling)
- Contraction period = increase in muscle tension due to crossbridge formation and movement
- Relaxation period = decrease in muscle tension because of calcium removal –> regulatory proteins reposition
Treppe / Staircase phenomenon
- stepping up of tension during multiple stimuli until uniform tension is reached
- step-wise increase of calcium availability, blood flow, heat, and efficiency of enzymes
- frequency and strength of stimulus are held constant
Temporal / wave summation
- increase the frequency of stimulation over time
- 2nd stimulation arrives before relaxation of the 1st
- 2nd contraction is bigger because of residual calcium
Twitch –> incomplete tetanus –> complete tetanus
tetany
sustained contraction without relaxation
motor unit
- motor neuron and muscle fibers it stimulates with its branching axon
- precise movements controlled by many small motor units
approximate number of ennervated muscle fibers by motor units for eye movement, arm movement, and voice production
10-20
2000-3000
2-3
what makes a contraction stronger?
the size of the motor units and the number of motor units that are activeated
what sized motor units are recruited first?
smaller ones
spatial summation / motor unit recruitment
- subthreshold stimuli = no observable contraction
- threshold stimuli = stimulus casing 1st observable contraction
- maximal stimulus = strongest stimulus that increases contractile force
Isotonic contraction
tension developed remains constant while muscle changes in length
- body movement and moving objects
- picking up a book
isometric contractions
- tension developed isn’t enough for object to be moved and muscle length doesn’t change
- holding a book with an outstretched arm
length-tension relationship
when muscle fibers are stretched, there’s less overlap bt filaments, so tension decreases
when muscle fiber is shortened, filaments are compressed, so less myosin heads make contact with thin filaments and there’s less tension
optimal muscle length is in between the two
