Question

Describe how the motor unit causes neurotransmitter release from the synaptic bulb at the neuromuscular junction.

Answer 1

A motor unit is made up of a motor neuron and a skeletal muscle which gets innervation by that motor neuron. Each motor neurons synapses with many muscle fibres.

A neuromuscular junction is the a chemical synapse between a motor neuron and a muscle fiber.

Neurotransmitters are chemical messengers which transfer signals from the neuron to muscle fibre.

Molecules of neurotransmitters are stored in small vesicles in presynaptic nerve terminal. They help to transport impulses across neuromuscular junction.

When an impulse reaches nerve terminal, it causes neurotransmitter to be released into the synaptic cleft.

It involves following steps:

• An action potential reaches presynaptic nerve terminal results in depolarization
• Activation of voltage gated Ca2+ channels
• Ca2+ enters the nerve terminal
• It causes confirmational change in specific protiens in synaptic vesicles
• Fusion of vesicle to the plasma membrane of nerve terminal.
• Fusion causes the neurotransmitters in the vesicle to spill out into the synaptic cleft
• They diffuse toward the receptors on the postsynaptic cell