GROSS ANATOMY

Detailed explanation-1: -Pupil dilation is mediated by a sympathetic output acting in opposition to parasympathetically mediated pupil constriction. While light stimulates the parasympathetic output, giving rise to the light reflex, it can both inhibit and stimulate the sympathetic output.

Detailed explanation-2: -Oculomotor nerve (III) is responsible for the control of the pupil (constriction) via parasympathetic fibres (this is opposed by dilator tone controlled by sympathetic pathways).

Detailed explanation-3: -Stimulation of the sympathetic pathway results in the release of norepinephrine onto -adrenergic receptors on the sphincter dilator, dilating the pupil and increasing the activation of light receptors in the retina.

Detailed explanation-4: -Your pupils get bigger or smaller, depending on the amount of light around you. In low light, your pupils open up, or dilate, to let in more light. When it’s bright, they get smaller, or constrict, to let in less light. Sometimes your pupils can dilate without any change in the light.