3.4 - Mechanics of Muscle Contraction & Body Movement Flashcards
Compared to slow twitch fibres, fast twitch fibers can generate more or less tension?
More tension
What factors influence tension exerted by a muscle during a single twitch?
- muscle type (slow twitch vs. fast twitch)
- sarcomere length at the start of contraction
What is the sarcomere length determined by?
the degree of overlap between thick and thin filaments
What happens if there is too little overlap?
- few cross-bridges
- little force can be generated
What happens if there is too much overlap?
- actin filaments interfere with each other
- less force generated
What happens if there is way too much overlap?
- thick filaments collide with Z disk
- force rapidly decreases
TRUE OR FALSE:
A single twitch represents the maximum force a muscle fibre can produce
FALSE
The force of a muscle fibre can be increased by ___
increasing the rate of action potentials firing to stimulate the fibre
What is summation? When does it happen?
- increase in force generated by a muscle
- Due to repeated stimulation from action potentials before muscle has fully relaxed
What is tetanus?
state of a muscle when it reaches maximum force of contraction
Define incomplete/unfused tetanus
- slow stimulation rate
- muscle fibre relaxes slightly b/w stimuli
Define complete/fused tetanus
- fast stimulation rate
- muscle fibre does not have time to relax b/w stimuli
What is a motor unit?
basic unit of contraction in an intact skeletal muscle
A motor unit is composed of:
- group of muscle fibres
- the somatic motor neuron that controls them
TRUE OR FALSE:
In a single motor unit, muscle fibres can be of both fast-twitch and slow-twitch muscle fibre types.
FALSE
All muscle fibres of a single motor unit are of the same muscle fibre type; either fast-twitch or slow-twitch
An action potential in the somatic motor neuron leads to what?
contraction of all muscle fibres in each motor unit
TRUE OR FALSE:
Muscle units contract in an all-or-none fashion
TRUE
Contraction of the muscle can be varied by?
- changing the type of motor unit that is activated
- changing the # of active motor units (# of motor units firing)
Explain recruitment as it relates to contraction
- force of contraction is increased by using more motor units
- different muscle fibres are recruited at different times
- slow oxidative fibres = low threshold for stimulation
- fast glycolytic fibres = high threshold for stimulation
Which will have more muscle fibres per motor unit, those involved in fine or coarse movement?
Coarse movements = 1 single motor neuron controls a lot more muscle fibres in a single motor unit
What are the 2 main types of muscle contraction?
- isotonic
- isometric
______ contraction creates force and movement while ______ contraction creates force without movement
isotonic = force + movement isometric = force only
During _____ contraction, muscle length changes while muscle length is constant during _____ contraction
- isotonic
- isometric
Why can’t movement be produced during isometric contractions?
because the load is larger than the force applied by the muscle
How can an isometric contraction create force if there is no change in muscle length?
- sarcomeres still shorten
- elastic components stretch to take up force until fully stretched
