Motor units - summation

• Neuromuscular System

  The nervous system and the muscles work together to allow movement
• Sympathetic nervous system

  Prepares the body for exercise. Flight or fight response
• Parasympathetic nervous system

  Relaxes the body and slows down the high energy functions
• Slow Oxidative (Type 1)

  They have a slower contraction speed and produce most of their energy aerobically. They're used for lower intensity exercise (EG - Long distance running)
• Fast Twitch (Type 2)

  These muscle fibres have a faster contraction and a greater contraction force. They produce energy anaerobically and fatigue quickly. There are 2 types
• Fast Glycolytic (Type 2b)

  Provide a quick, short burst of energy so are used for highly explosive events, such as 100m
• Fast Oxidative Glycolytic (Type 2a)

  These provide a longer burst of energy, as the fibres are more resistant to fatigue, so are used for events such as 1500m
• Hypertrophy

  Where the muscle has become bigger and stronger
• Motor unit

  A motor neurone and its muscle fibres
• Motor neurone

  Nerve cells which transmit the brains information as electrical impulses to the muscles
• Muscle spindle

  Type of proprioceptor that detects how far and how fast a muscle is being stretched and produce a stretch reflex
• Golgi Tendon Organs

  Type of proprioceptor that is activated when there is tension in a muscle (PNF). They are found between muscle fibres and the tendons
• Isometric contraction

  Where there is tension in a muscle but no visible movement
• All or None law

  Where a sequence of impulses has to be of sufficient intensity to stimulate all of the muscle fibres in a motor unit in order for them to contract. If not none of them contract
• Threshold

  A minimum amount of stimulation that is required to start a contraction
• Wave Summation

  Where there is a repeated nerve impulse with no time to relax, so a smooth, sustained contraction occurs, rather than twitches. Calcium builds up in the muscle cell as there is no time for the muscle to relax
• Tectonic contraction

  A sustained muscle contraction caused by a series of fast repeating stimuli
• Spatial summation

  When the strength of a contraction changes by altering the number and size of muscles motor units
• Aerobic

  Using oxygen
• Anaerobic

  Without oxygen
• Neuromuscular junction

  Where the motor neurone and the muscle fibre meet
• Autogenic inhibition

  Where there is a sudden relaxation of the muscle in response to high tension. The receptors involved in this process are Golgi Tendon Organs
• How does spatial summation work to increase force ?

  Impulses are received at the same time at different places on the neurone which add up to fire the neurone. It involves the recruitment of additional, bigger motor units and fast twitch fibres within a muscle to develop more force. Activation of these motor units is staggered which enables a sustained muscle contraction to be maintained as some motor units are contracting and others are relaxing - delaying fatigue.