A 68-year-old man with a history of benign prostatic hyperplasia and urinary retention presents to the emergency department with acute angle-closure glaucoma. His intraocular pressure (IOP) is 58 mmHg, and he has corneal edema and a mid-dilated pupil. The ophthalmologist prescribes pilocarpine drops immediately. Within 2 hours, his IOP drops to 32 mmHg. However, the patient develops severe bronchospasm, profuse salivation, and bradycardia (HR 42/min). Which of the following best explains the adverse effect profile observed in this patient?