Skeletal Muscle Contractions

• Motor Neurons

  specialised cells which transmit nerve impulses rapidly to a group of muscle fibres

  they have a cell body in the brain or spinal cord with an extending axon which branches to connect motor end plates to a group of muscle fibres
• Motor Unit

  the motor neuron & its muscle fibres are termed the motor unit

  functions to carry nerve impulses from the brain & spinal cord to the muscle fibres initiating muscular contraction
• All or None Law

  when all the muscle fibres within a motor unit contract completely or not at all

  this increases/decreases the rate of stimulation, which increases the force of contraction
• Skeletal Muscle Contractions Process

  1. nerve impulse is initiated in the motor neuron cell body
  2. nerve impulses conducted down the axon of the motor neuron by a nerve action potential to the synaptic cleft
  3. neurotransmitter called acetylcholine is secreted into the synaptic cleft to conduct the nerve impulse across the gap
  4. if the electrical charge is about the threshold, the muscle fibre will contract
  5. this happens in an 'all or none fashion'