Motor units

• What are motor neurones?

  motor neurones are specialised cells which transmit nerve impulses to the skeletal muscle fibre, causing them to contract and therefore create movement.
• What makes up the motor unit?

  The motor neurone, axon and associated muscle fibres.
• Definition of a motor neurones?

  A nerve cell which conducts a nerve impulse to a group of muscle cells.
• Definition of the axon?

  Part of the motor unit, this passes the impulse to the muscle.
• Definition of the motor end plate?

  The point at which the axon joins the muscle fibres.
• What process does the nerve impulse use to create muscular movement?

  And electrochemical one.
• What is the definition of action potential?

  Positive electrical charge inside nerves and muscle cells which conducts the nerve impulses down the neurone and into the muscle fibres
• What is the point of which the axons motor end plates meet the muscle called?

  The neuromuscular junction
• What is the synaptic cleft?

  The small gap between the motor end plate and the muscle fibre
• What does the nerve action potential do?

  Conducts the nerve impulses down the neurone and into the muscle fibre
• What is a neurotransmitter?

  A chemical (Acetycholine) which is secrete by the neurone which transmits the nerve impulses across the synaptic cleft
• What is the all-or-none law?

  When a muscular unit receives a stimulus and creates an action potential that reaches a threshold charge. All the muscles will contract at the same time and with maximum force. If the threshold charge isn’t met, none of the fibres will contract.
• What is the flow diagram of the motor unit?

  • Nerve impulse in initiated by motor neurone cell body
  • Nerve impulse conducted down axon of the motor neurone by a nerve action potential to the synaptic cleft
  • Neurotransmitter called acetylcholine is secreted into the synaptic cleft to conduct nerve impulses over a gap
  • If the electrical charge meets/is above the threshold then muscle fibres will contract
  • This happens in an all-or-none fashion