The Motor Unit Flashcards
What are the features of the motor unit?
• A skeletal muscle only contracts when stimulated by an electrical impulse sent from the CNS.
• Motor neurons are specialised cells which transmit nerve impulses 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 neuron and its muscle fibres are the motor unit.
What happens at the motor unit?
1) Nerve impulse initiated in the motor neuron cell body.
2) Nerve impulse conducted down axon of motor neuron by nerve action potential to synaptic cleft.
3) Neurotransmitter called acetylcholine is secreted into synaptic cleft to conduct nerve impulses across gap.
4) If electrical charge is above a threshold, the muscle fibre will contract.
5) This happens in ‘all or none fashion’.
