What happens to pupils when the parasympathetic system is slowed down by drugs like heroin?

When the parasympathetic nervous system is slowed down by substances such as heroin, a notable effect is the constriction of pupils, often referred to as miosis. Heroin, being an opioid, stimulates the body’s opioid receptors and leads to a sedative effect, which greatly influences the autonomic nervous system functions, particularly those controlled by the parasympathetic system.

In typical physiological terms, when the parasympathetic system is functioning properly, it promotes rest and digestion, often leading to reduced heart rate, increased salivation, and constricted pupils. However, when this system is suppressed or slowed down by opioids like heroin, the usual response of pupil dilation from the sympathetic nervous system predominates. Thus, the pupil response to heroin is constriction, because the drug intensifies the activity of the parasympathetic system while also inhibiting the sympathetic response.

Understanding pupil response in this context is critical in assessing opioid intoxication, as pupils that are notably constricted can be indicative of drug use, helping healthcare professionals recognize and respond to potential overdose situations effectively.