Motor units

• Motor unit


  • Consists of a motor neuron and a number of muscle fibres
  • Carries a nerve impulse from the CNS to the muscle fibres
• Nervous stimulation of a motor unit


  1. Stimulus causes an action potential

  2. Release of sodium/NA+ ions causes depolarisation

  3. Neurotransmitter/acetylcholine is released

  4. Transmits the nerve impulse across the synaptic cleft to the muscle

  5. Impulse stimulates motor unit/muscle fibres/causes wave of contraction/causes muscles to contract
• All or none law

  All fibres within a motor unit contract (or none contract)
• Stimulating more motor units


  Increases the force/strength of muscle contraction