All or None Law

• What is required for a skeletal muscle to contract?

  An electrical impulse sent from the CNS
• What role do motor neurones play in muscle contraction?

  They transmit signals rapidly to the muscle fibre
• What is a motor unit?

  A motor neurone linked to a muscle fibre
• What happens when the motor neurone is activated?

  Positive sodium ions (Na+) diffuse into the axon
• What does the diffusion of sodium ions trigger?

  An action potential
• What is an action potential?

  A positive electrical charge that creates an impulse down the axon
• Where does the action potential travel to?

  Down the axon to the muscle fibre
• What is located at the end of the axon?

  The synapse
• What are the axon terminals?

  Structures at the end of the axon
• What are motor end plates?


  They are located at the end of the axon terminals and meet the muscle fibres
• What are neuromuscular junctions?

  They are formed when motor end plates meet muscle fibres
• What is required for a skeletal muscle to contract?

  An electrical impulse sent from the CNS
• What role do motor neurons play in muscle contraction?

  They transmit signals rapidly to the muscle fibre
• What is a motor unit?

  A motor neuron linked to a muscle fibre
• What happens when the motor neuron is activated?

  Sodium ions diffuse into the axon
• What does the diffusion of sodium ions trigger?

  An action potential
• What is an action potential?

  A positive electrical charge that creates an impulse down the axon
• Where does the impulse travel to after the action potential is generated?

  To the muscle fibre
• What is located at the end of the axon?

  The synapse
• What are the axon terminals?

  Structures at the end of the axon
• What are motor end plates?

  They are structures that meet with muscle fibres at the neuromuscular junctions
• What is the neuromuscular junction?

  The junction where motor end plates meet muscle fibres
• What is the synaptic cleft?

  A gap at the neuromuscular junction where the nerve impulse travels
• What neurotransmitter is involved in muscle contraction?

  Acetylcholine
• What happens if enough acetylcholine is secreted?

  A muscle action potential is created, leading to muscle contraction
• What is the all-or-none law in muscle contraction?

  If the electrical impulse reaches a certain threshold, the muscle contracts fully
• What is the point where the axon’s motor end plate meets the muscle fibre called?

  Neuromuscular junction
• What is the gap between the end plate and the muscle fibre known as?

  Synaptic cleft
• What happens when an impulse reaches the end plate of a muscle fibre?

  It stimulates the vesicle to release the neurotransmitter acetylcholine (Ach)
• What is the role of acetylcholine (Ach) in muscle contraction?


  It is secreted across the synaptic cleft to transmit the action potential
• What occurs if acetylcholine (Ach) is secreted above a threshold?

  The action potential will be transmitted into a muscular contraction
• What is the all or none law in relation to motor units?

  If a motor unit receives a sufficient stimulus, all muscle fibres will contract at maximum force
• What happens if the action potential does not reach the threshold in a motor unit?


  None of the fibres will contract
• What are the key components involved in the neuromuscular junction process?

  • Neuromuscular junction: meeting point of axon and muscle fibre
  • Synaptic cleft: gap between end plate and muscle fibre
  • Acetylcholine (Ach): neurotransmitter released to stimulate contraction
  • Action potential: triggers contraction if Ach exceeds threshold
• What are the implications of the all or none law for muscle contraction?

  • All muscle fibres in a motor unit contract simultaneously if threshold is reached
  • No contraction occurs if the threshold is not met
  • Ensures coordinated and maximum force generation in muscle units
• What is required for a skeletal muscle to contract?

  An electrical impulse sent from the CNS
• What is a motor unit?

  A motor neurone linked to a muscle fibre
• What ions diffuse into the axon when the motor neurone is activated?

  Positive sodium ions (Na+)
• What triggers an action potential in the motor neurone?

  The diffusion of sodium ions into the axon
• What is the action potential?

  The positive electrical charge that creates an impulse down the axon