Constriction of pupils is seen in: September 2005
**Core Concept**
The constriction of pupils is a response to light, mediated by the autonomic nervous system, involving the parasympathetic nervous system's stimulation of the iris sphincter muscle. This response helps regulate the amount of light entering the eye.
**Why the Correct Answer is Right**
The correct answer involves the stimulation of the parasympathetic nervous system, which releases acetylcholine (ACh) from the Edinger-Westphal nucleus. ACh acts on muscarinic receptors in the iris sphincter muscle, causing it to contract and constrict the pupil. This is a classic example of a parasympathetic response, involving the release of a neurotransmitter that stimulates a specific effector organ.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because constriction of pupils is not typically associated with sympathetic nervous system activity, which would instead cause dilation of the pupils through the release of norepinephrine from the superior cervical ganglion.
* **Option B:** This option is incorrect because constriction of pupils is not a characteristic of the somatic nervous system, which is responsible for voluntary movements, not autonomic responses.
* **Option C:** This option is incorrect because constriction of pupils is not a response to the release of dopamine, which is involved in other physiological processes.
**Clinical Pearl / High-Yield Fact**
The pupillary light reflex is a critical aspect of neuro-ophthalmology, and any abnormalities in this reflex can indicate underlying neurological or ophthalmological conditions, such as third nerve palsy or Adie syndrome.
**Correct Answer: B. Adie syndrome**