Skeletal Muscle Contraction

• Skeletal muscles only contract when stimulated by electrical impulses from the central nervous system.
• A nerve impulse is initiated in the motor neuron. The impulse is conducted down the axon of the motor neuron by a nerve action potential. A neurotransmitter (acetylcholine) is secreted into the synaptic cleft to conduct the impulse across the gap to contract the muscle.
• All or none law: If the electrical charge is above threshold, muscle fibre contracts. Either all muscle fibres give a complete contraction, or no contraction at all.
• Motor Neurons: specialised cells which transmit nerve impulses to muscle fibres.
• Action Potential: positive electric charge in nerve and muscle cells which conducts the impulse.
• Axon: branches off nerve cells to connect to muscle fibres (at the neuromuscular junction).
• Synaptic Cleft: gap between axon motor end plates and msucle fibre.