Final answer:
The statement is true; acetylcholine (ACh) does diffuse across the synaptic cleft and bind to receptors on the motor end plate, which can initiate muscle contraction.
Step-by-step explanation:
The statement that 'ACh released by a motor neuron crosses the synaptic cleft and reaches the motor end plate by diffusion' is true.
When an action potential arrives at the axon terminal of a motor neuron, it leads to the opening of voltage-gated calcium channels, allowing the influx of calcium ions.
This triggers the synaptic vesicles to merge with the presynaptic membrane and release acetylcholine (ACh) into the synaptic cleft.
Acetylcholine then diffuses across the cleft and binds to the ACh receptors located on the muscle cell's motor end plate.
As ACh binds, it opens ion channels that allow an influx of sodium ions into the muscle cell, initiating a depolarizing event known as an end-plate potential.
This depolarization ultimately leads to muscle contraction through the generation of an action potential.