Which of the following is true about acetylcholine being released?

Acetylcholine is a neurotransmitter that plays a crucial role in the communication between nerve cells and muscle fibers at the neuromuscular junction. When a nerve impulse reaches the end of a motor neuron, acetylcholine is stored in synaptic vesicles and released into the synaptic space (the small gap between the nerve ending and the muscle fiber). This release occurs through a process called exocytosis, where the vesicles fuse with the cell membrane, releasing acetylcholine into the synaptic cleft. The presence of acetylcholine then binds to receptors on the muscle fibers, leading to muscle contraction.

The other options suggest processes that do not accurately describe the function or behavior of acetylcholine. For instance, it isn't absorbed directly by muscle fibers or synthesized in the muscle itself; rather, it is synthesized in the neuron before being released. Additionally, while acetylcholine does play a role in neural communication, it does not activate electrical impulses in the brain directly; its main function occurs at the neuromuscular junction, influencing muscle contraction.