Muscualr System Flashcards
What is a motor unit
Motor unit - a motor neurone attached to a group of the same muscle fibre types (can’t have diff types attached). Muscles made of thousands of motor units of all three muscle fibre types
How does wave summation control the strength of a muscle contraction
Wave summation - controls strength of muscle contraction by determining the force (tetanic response) a motor unit will apply. Does this by changing the frequency of nerve impulses arriving at muscle fibres. Eg high frequency (no time to relax between twitches) = high force and smooth sustained contraction (tetanus) —> allows rugby player to kick the ball with more force during a conversion that is a long way away or kick the ball during play to gain territory
How does spatial summation control the strength and duration of a muscle contraction
Strength - size + no. of motor units recruited will determine the force applied - eg many large motor units (fast twitch) simultaneously =max force, low numbers of small motor units (slow) = low force —> can recruit fast muscle fibres to create large force during scrums inorder to maintain advantage of scrum and not collapse or during a tackle to stop player from easily running past
Duration - allowing some motor units to rest, while others recover (still applying necessary force) means they can be rotated. So recovered can take over contraction while others rest (revivers time varies) —>allows rugby players to continue to have required force in scrums and tackles throughout match
What is the all or none law
All or none law - for any motor unit to generate a contraction the stimulus received by the CNS must be over the threshold/be great enough to initiate a nerve impulse. Not possible to have a partial contraction
What are the 3 types of muscle fibres
- Slow oxidative (type1)
- Fast oxidative glycolytic (type 2a)
- Fast twitch glycolytic (type 2b)
When would type 1 be used in sport
Predominantly by a marathon runner (aerobic endurance based activity)
When would type 2a be used in sport
Predominantly in a 100m swim race as strength, power required as well as form of endurance
When would type 2b be used in sport
Predominantly used in a 100m sprint as requires working maximally and anaerobically
Functional + structural characteristics of type 1
High aerobic capacity
Fatigue resistant
Small
Slow speed of contraction
Low force of contraction
Greatest capacity to store muscle triglycerides
Functional + structural characteristics of type 2a
Fast speed contraction
Medium aerobic capacity
Large
High force of contraction
Less resistant to fatigue
Functional + structural characteristics of type 2b
High anaerobic capacity
Easily fatigued
Large
Fast speed of contraction
Largest store of pc
What is pnf
Proprioceptive neuromuscular facilitation - adv stretching technique
What is crac
Type of pnf (contract - relax - antagonist - contract)
Describe crac
- Individual performs passive stretch, muscle spindles (type of proprioceptors (sensory receptors)) between skeletal muscle fibres detect stretch.
- If stretched too far muscle spindles send exitory signals to cns to initiate stretch reflex
- individual isometrically contracts muscle for 10 secs which activates Golgi tendons (between muscle fibre + tendons)
- Golgi tendons sends inhibitory signals to override excitory signals this delays the stretch reflex which allows antagonist to relax + lengthen (autogenic inhibition)
- allows muscle to stretch further during a passive stretch — Inc Rom
Benefits of pnf
- Inc joint rom
- Inc muscle flexibility
- Inc muscle strength
Drawbacks of pnf
- Inc risk of injury (Inc Rom too far)
- not good for young athletes
