A16- Neuromuscular system

• what is the 'all or none law'?

  the impulse travelling down a motor neurone must exceed the threshold, if it does it will cause all muscle fibres to contract maximally and at the same time.
• define motor unit?


  consists of a single motor neuron and all the muscle fibres supplied by that neuron
• define motor neuron?


  nerve cells which transmit the brain's instructions through electrical impulses to the muscles
• define neuromuscular junction?


  where the motor neuron and muscle fibre meet
• the muscle can only contract if calcium is present
• all muscle fibres within a motor unit will be the same type (fast/slow twitch)
• fast twich motor neuron has a larger diameter. impulses therefore travel quicker. the quicker the impulse causes faster contractions= more force
• the number of muscle fibres within a motor unit depends on the degree of accuracy and power required
• eye: as few as 5 muscle fibres joined to one motor neuron, provides precision, accuracy, fine control.
• Hamstring: as many as 1000 muscle fibres joined to one motor neuron, provides force and power
• what acronym is used to remember how muscles vary the force of contraction?

  F: Frequency

  A: Amount

  S: Size

  T: Type
• ForceofC: define frequency?


  recruiting motor units via wave or spatial summation
• what is spatial summation?


  some motor units are contracting, whilst others are relaxing (recovery), ATP consumption and workload is shared across motor units (muscle)

  Fatigue is evenly distributed (delay fatigue)

  used during prolonged endurance events

  E.g long distance running
• What is wave summation?


  • flood motor unit with electrical impulses
  • next impulse arrives, before motor unit has had time to relax
  • accumulation of impulses leads to 'tetanic contraction'
  • produces maximal force
• what is a tetanic contraction?


  a sustained muscle contraction caused by a series of fast repeating stimuli
• ForceofC: define amount?

  recruiting more or fewer motor units
• Amount: fewer/more=?


  recruit fewer motor units= less force, more accuracy and precision

  recruit more motor units= more power and force, less accuracy
• ForceofC: define Size?

  recruiting smaller or larger motor units
• Size: smaller vs larger motor units?


  Recruit smaller motor units (fewer muscle fibres) for smaller force and accuracy. e.g darts

  Recruit larger motor units (more muscle fibres) for stronger force and power. e.g 100m sprint
• ForceofC: define Type?


  the type of motor unit (muscle fibre) recruited
• Type: fast vs slow twitch?


  Recruit fast twitch motor units (fast twitch muscle fibres) for greater force and faster speed of contraction. e.g 100m sprint

  Recruit slow twitch motor units (slow twitch muscle fibres) for smaller force and slower speed of contraction. e.g darts
• define muscle spindles?


  muscle spindles are sensitive proprioceptors that lie between muscle fibres. They consist of smaller intrafusal muscle fibres (normal fibres are called extrafusal fibres).
• What do muscle spindles detect?

  they detect length and speed of stretch.

  When a muscle is stretched the spindles stretch and send sensory impulses to the CNS. If the CNS believes the muscle is stretching too far too quickly it will control the movement by initiating the stretch reflex which causes the muscle to shorten.

  In this way the spindles are a safety mechanism. - the respomse to initiate a stretch reflex
• What are the 3 phases to the stretch reflex from muscle spindles?


  1. detects speed and length of stretch
  2. sends impulse to CNS via the sensory neuron
  3. sends impulse to muscle to concentrically contract
• define golgi tendon organs?

  these are found between tendon fibres and relay sensory impulses to the CNS about the state of tension in them.
• how do golgi tendon organs react?

  (they are similar to muscle spindles in that theyre a protection mechanism)

  they respond when the tension or force becomes excessive and causes the muscle to relax (the opposite of the stretch reflex) - autogenic inhibition
• what is autogenic inhibition?

  Autogenic inhibition= there is a sudden relaxation of the muscle in response to high tension detected by the goligi tendon organs
• what are the 3 phases to the autogenic inhibition?


  1. detect load and muscle tension
  2. send impulse to CNS via the sensory neuron
  3. 'GTO Response' - inhibitory impulses are sent via the motor neuron to the muscle to cause it to relax. this is called autogenic inhibition.
• muscle spindles- detect, response, outcome?

  Detect: speed and length of stretch

  Response: send impulse via sensory neuron to CNS

  Outcome: Stretch Reflex- an impulse is sent down the motor neuron to cause a concentric contraction
• Golgi Tendon Organs- detect, response, outcome?

  Detect: load and muscle tension

  Response: send impulse via sensory neuron to CNS

  Outcome: Autogenic inhibition- an inhibitory impulse is sent down the motor neuron to cause the muscle to relax
• define PNF?


  Proprioceptive Neuromuscular Facilitation
• define flexibility?


  the range of movement at a joint
• what does CRAC technique stand for?

  contract-relax (type1) / antagonist-contract (type 2)

  type 1= autogenic inhibition

  type 2= reciprocal inhibition
• What is PNF?


  an advanced and effective form of flexibility training. The technique is known as CRAC Technique.
• What is the Plyometrics technique, The contract relax phase?


  an individual performs a stretch with help of a partner until tension if felt. the muscle spindles detect the stretch and should initiate a stretch reflex. However if the performer isometrically contracts the muscle for 10secs by pushing against the partner, this puts tension on the muscle and activates the Golgi tendon organ and inhibitory signals are sent causing the muscle to relax and lengthen (autogenic inhibition) overriding the strech reflex. This process is repeated until no gains or possible.
• What are the 3 steps to PNF stretching?

  Step 1:

  the athletes hamstring is stretched to its limit by a partner --> this stimulates the muscle spindles

  Step 2:

  the athlete then pushed back against their partner, isometrically contracting their hamstring for 10secs --> this stimulates the golgi tendon organs

  Step 3:

  The GTO response overrides the stretch reflex --> the relaxed muscle is then able to be stretched further by their partner

  
  

  (often repeated 3 times)
• what are the 4 strengths to PNF stretching? (gymnastics, athletics, games player)

  • increased range of movement at a joint
  • Gymnastics- enables them to create more advanced/complex moves, makes movement more aesthetically pleasing.
  • Athletics- enables a sprinter to have more efficient technique, generate more muscular force and speed.
  • games player- helps prevent injury
• what are the 3 limitations to PNF stretching?

  • flexibility is not always the most important component of fitness to improve.
  • You need to ensure you have warmed up effectively- overriding the stretch reflex increases the risk of injury
  • PNF stretching reduces speed and power if done just prior to performing