Mechanism
When light activates the melanopsin signaling system, the melanopsin-containing ganglion cells discharge nerve impulses, which are conducted through their axons to specific brain targets. These targets include the olivary pretectal nucleus (OPN) (a center responsible for controlling the pupil of the eye) and, through the retinohypothalamic tract, the suprachiasmatic nucleus of the hypothalamus (the master pacemaker of circadian rhythms). Melanopsin-containing ganglion cells are thought to influence these targets by releasing from their axon terminals the neurotransmitters glutamate and pituitary adenylate cyclase activating polypeptide (PACAP). Melanopsin-containing ganglion cells also receive input from rods and cones that modifies or adds to the input to these pathways.
Read more about this topic: Melanopsin
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