The pupil is constricted or dilated by the smooth muscle in the iris. Increased release of acetylcholine by the parasympathetic nervous system (rest and digest reaction) causes contraction of the circular smooth muscle. This makes the pupil (the dark hole) smaller – miosis (also spelled myosis as you can see in the picture). Drugs that cause pupillary constriction include heroin, morphine, codeine, fentanyl, demerol, methadone, and oxycontin.
Fun fact: miosis comes from the ancient Greek word “to close the eyes”
Increased release of norepinephrine by the sympathetic nervous system (fight or flight reaction) causes contraction of the radial smooth muscle. This makes the pupil (the dark hole) larger - mydriasis. Here are some drugs that cause pupillary dilation:
- CNS stimulants: cocaine, amphetamines, methamphetamine
- Hallucinogens: LSD, ecstasy
- Cannabis: marijuana, hashish, marinol
Answer: (D). Morphine
The dental hygiene board exams (NBDHE, NDHCE) put a lot of emphasis on pharmacology. Therefore, review this chapter very thoroughly.
Lastly, I just wanted to share how I remember parasympathetic and sympathetic nervous systems. Think about a time you ate too much. You feel “PARAlyzed (food coma)” and need to “rest.” This helps me remember PARAsympathetic with “REST and digest system.” The sympathetic system is the opposite and is called “fight or flight response.” Why am I talking about the sympathetic and parasympathetic nervous system? Because pupil dilation and contraction result from those natural body responses.
Feel free to ask anything related to the dental hygiene board exams (NBDHE, NDHCE). Our goal at StudentRDH is to make you successful wherever you are!
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