乙酰胆碱在肌肉收缩过程中起着关键作用。

___Acetylcholine plays a vital role in muscle contraction.

乙酰胆碱在神经系统中起着传递信号的重要作用。

___Acetylcholine plays a crucial role in transmitting signals within the nervous system.

医生给患者注射了乙酰胆碱来调节他的心率。

The doctor injected ___acetylcholine to regulate the patient's heart rate.