neuromuscular system

• What does a motor unit consist of?

  A motor neurone and muscle fibres that it stimulates

  Motor neurone transmits nerve impulse to each muscle fibre to contract
• How many neurones stimulate a bundle of fibres?

  1
• How many types of muscle fibres can be found in a motor unit?

  1
• How do motor units vary in size?

  Each muscle is made up of many motor units and vary in size and type

  Small muscles will have motor units that only have a few fibres per neurone

  Large muscles will have a motor neurone that feeds hundreds of fibres
• What makes up the mixture of fibres?

  Genetics

  Skeletal muscles contain a mixture but are not equal
• Can you change the mixtures of fibres?

  No, but you can train to improve existing fibres

  eg sprinter will train to improve size of the size of their fast twitch type 2X fibres
• What are the 3 types of muscle fibres?


  Slow twitch type 1

  Fast twitch/ fast oxidative glycolytic type 2A

  Fast twitch/ fast glycolytic type 2X
• What are the structural characteristics of slow twitch type 1 fibres? (7)

  Small muscle fibre diameter

  High mitochondrial density

  High capillary density

  High myoglobin stores

  High oxidative enzymes

  Low PC stores

  Low glycogen stores
• What are the functional characteristics of slow twitch type 1 fibres? (7)

  Slow contraction speed

  Slow motor neurone conduction speed

  Low force production

  Low fatiguability

  Very high aerobic capacity

  Low anaerobic capacity, (low PC and glycogen stores, low ATPase activity, low glycolytic enzyme activity)

  Low ATPase activity
• Why do slow twitch type 1 fibres have a high aerobic capacity?

  High capillary density supplies top 1 fibres with large amounts of oxygenated blood

  High myoglobin content means more of this oxygen is pulled into muscle cells, (myoglobin has higher affinity of oxygen than haemoglobin)

  High number of mitochondria in muscle cells means extra O2 can be used to resynthesise ATP for energy

  Ability of type 1 fibres to us oxygen more readily makes them highly resistant to fatigue and increases VO2 max and aerobic power
• Applying slow twitch type 1 fibres to sporting examples


  Higher VO2 max and increased lactate thresholdwill allow a long distance runner to run at a faster speed for longer without fatigue. This will give the runner afaster timecompared to an athlete with a high % of type 2A or 2X fibres. Theirposition will be determinedby their aerobic capacity and is much more important than speed in finishingRecruit type 1 fibres in muscles of leg during a 1500M to allow forsustained muscle contractionsto last duration of raceFootballer will recruit type 1 fibres in legs during periods of recovery eg jogging into position or sustaining sub maximal effort for 90 mins
• What are the structural characteristics of fast twitch/fast oxidative glycolytic type 2A muscle fibres?

  Large muscle fibre diameter

  Intermediate mitochondria density

  Intermediate capillary density

  Intermediate myoglobin stores

  High PC stores

  High glycogen stores
• What are the functional characteristics of fast twitch/fast oxidative glycolyitc type 2A muscle fibres?

  Fast contraction speed

  Fast motor neurone conduction speed

  High force production

  Intermediate fatiguability

  Intermediate aerobic capacity

  High anaerobic capacity

  High ATPase activity

  Properties of both fast and slow twitch muscle fibres
• Applying fast twitch/fast oxidative glycolytic type 2A fibres to sporting examples


  Used for speed/endurance in events like 400m-800m sprints. Will be recruited as the demands of the race increase to moderate intensity

  Midfield in football will recruit type 2A fibres in the legs during extended sprints eg sprinting from box to box or maintaining possession whilst being tracked down by opposition
• What are the structural characteristics of fast twitch/fast glycolytic 2X muscles fibres?

  Large muscle fibres density

  Low mitochondrial density

  Low capillary density

  Low myoglobin stores

  Very high PC stores

  Very high glycogen stores

  Very high glycolytic enzyme activity
• What are the functional characteristics of fast twitch/ fast glycolytic 2X muscle fibres?

  Fast contraction speed

  Fast motor neurone conduction speed

  High force production

  High fatiguability

  Low aerobic capacity, (low mitochondria, low myoglobin, low capillary density)

  Very high anaerobic capacity

  Very high ATPase activity

  Large motor neurone
• Why do fast twitch 2X fibres have a high anaerobic capacity?

  Large motor neurone provides a greater impulse to more muscle fibres, resulting in a faster, stronger contraction

  The fast speed of contraction and high force of contraction of 2X fibres provides power athletes, such as sprinters, with speed and power o drive out of the blocks and fast acceleration

  High PC stores provide an increased energy source for ATP products vis ATP-PC system which fuels fast and powerful muscle contractions

  High glycogen stores provide an increased energy source for ATP production via anaerobic glycolytic system which fuels high intensity muscle contractions.

  High ATPase activity means ATP can be broken down faster to produce energy from ATP for high intensity muscle contractions through ATP-PC

  High glycolytic enzyme activity means there is an increased enzyme activity for ATP production within the lactate anaerobic system

  In sprints and power events they are short and quick so aerobic power is not required and fatiguability is not an issue
• Applying fast twitch/fast glycolytic type 2X fibres to sporting examples


  Used to dive off starting blocks in swimming as quickly as possible because they have a fast speed of contraction and high force of contraction

  Recruit type 2X fibres in the muscles of legs in high jump for an explosive contraction to lift the body over the bar

  Recruit type 2X fibres for explosive action such as jumping high to head the ball, moving quickly into a tackle or sprinting for the ball
• What are proprioceptors?


  Receptors that provide CNS with information about body position and detect movement within muscles
• What are the 2 two of proprioceptors?

  Muscle spindles

  Golgi tendon organs
• What is the function of muscle spindles

  Detect changes in muscle length/tension- how far and fast a muscle is stretched

  Send info to central nervous system and CNS sends message back to the muscle telling it to contract- initiates stretch reflex to prevent injury
• What do muscle spindles initiate?

  Stretch reflex
• What is a stretch reflex?


  Protective function to prevent overstretching of a muscle- shortening of muscle/ concentric contraction
• What is the function of Golgi tendon organs?

  Detect increases in tension and causes muscle to relax and lengthen
• What do Golgi tendon organs override?

  The stretch reflex- autogenic inhibition
• What is autogenic inhibition?

  When the stretch reflex is delayed due to Golgi tendon organs sending inhibitory signals to relax and lengthen the muscle
• What is an example of an advanced stretching technique to improve flexibility?


  PNF
• What does PNF stand for?

  proprioceptive neuromuscular facilitation
• What is the aim of PNF?

  To increase flexibility and override the stretch reflex
• What technique is used during PNF?

  CRAC
• What does CRAC stand for?

  Contract, relax, antagonist, contract
• What are the stages of PNF, (without proprioceptors)?

  Done with a partner

  Passive stretch in target muscle until tension is felt eg hamstring stretch. Stretched position is held for 30 seconds

  Isometric contraction is performed, (pushing agaisnt resistance given by partner) for 5-10s

  Muscle is relaxed

  Passive stretch of the target muscle is repeated again, able to go further
• What is the role of muscle spindles in PNF?

  When the muscle is in the first passive stretch, they send a message to CNS to initiate a stretch reflex/ concentric contraction/shortening of muscle to stop leg going further/ overstretching
• What is the role of the Golgi tendon organs during PNF?

  During isometric contraction they detect increase in tension of the tendons in target muscle

  Inhibitory signals are sent to the brain and therefore causes auto genie inhibition which overrides/delays the stretch reflex, muscle relaxes

  When the muscle goes through the last passive stretch, the Golgi tendon organs relax it and allow to move further though it's range of motion
• What are the benefits of PNF stretching?

  Most effective form of flexibility training for increasing range of motion

  Gymnastics and dance- allows performance of more advanced routines and performers can produce more aesthetically pleasing shaped with their bodies. This increases their scores and chances of success

  Swimming and sprinting- greater flexibility allows a more efficient technique to be used which can increase the speed of performer and decrease the effort required to travel at the same speed

  Football and rugby- can be used as an injury prevention method. A greater range of movement at the joints means players are likely to incur injuries such as strains and tears
• What are the drawbacks of PNF stretching?

  Very specialised training method, focusing just on improving flexibility, however in lots of sports, other components of fitness might be deemed more important such as anaerobic power in sprinting

  Due to the passive nature of stretches and overriding of stretch reflex, the risk of injury is increased if precautions such as a thorough warm up and a knowledgeable partner are not adhered to

  If performed immediately before activity, PNF stretching reduces power and speed, therefore is not an appropriate specialist training method during a warmup for sports requiring these components of fitness
• What is the law that controls a motor unit?

  All or none law
• What is the all or none law?

  At the synaptic cleft, a minimum amount of stimulation, (occurring from repeated nerve impulses,) needs to reach a threshold to release transmitter substance, (acetylcholine,) so the nerve impulse is able to cross and cause contraction the fibres in the motor unit

  If the sequence of impulses is equal to or more than the threshold, all the fibres in the motor unit will contract maximally- if not then no contraction
• What is the small gap where the motor neurone reaches the muscle fibres called?

  Synaptic cleft
• What is the transmitter substance called that is released when impulse has reached threshold?

  Acetylcholine