Motor Units Flashcards
What is a motor unit?
A motor neurone and it’s muscle fibres
What is the all or none law?
When a motor neurone stimulates its fibres, either all of them contract, or none of them contract
If the stimulus reaches the required threshold to start a contraction, all fibres contract, if not, then no fibres contract
What is wave summation?
When there is a repeated nerve impulse with no time to relax so a smooth, sustained contraction occurs rather than twitches
What is spatial summation?
When the strength of a contraction changes by altering the number and size of the muscles motor units
What is PNF (proprioceptive neuromuscular facilitation)?
An advanced stretching technique to improve flexibility
How is PNF used in practice?
- Hold limb until muscle is stretched and tension is felt- hold for 30s
- Isometrically contract the stretched muscle by pushing the leg forwards against the partner for 10s- partner should resist all movement
- The limb is pushed past it’s normal range of movement for 30s, then 30s recovery before repeating the procedure
What are muscle spindles?
Detect how far and how fast a muscle is being stretched and produce the stretch reflex
How do muscle spindles work?
If there is a sudden stretch in a muscle, the muscle spindles send an impulse to the CNS and an impulse is sent back to the same muscle, instructing that muscle to contract, this is called the stretch reflex, this prevents the muscle over stretching
What are Golgi tendon organs (GTO’s)?
Activated when there is tension in a muscle
How to GTO’s work?
When a muscle is isometrically contracted, GTO’s sense the increased tension in the tendon and send inhibitory signals to the CNS which allows the antagonist muscle to relax and lengthen- this is known as autogenic inhibition
Basically, the GTO’s override the stretch reflex so the muscle is relaxed and can be stretched
