>> Interesting. So is the rhodopsin in the human pineal gland functional -
>> in that it cycles between two configurations and that cycling is
>> essential to pineal function? Presumably, the cycling is no longer
>> driven directly by light, but then what does drive it?
It is light in humans.
However the signal goes via the sympathetic nervous system:
How does the retina transmit information about light-dark exposure to
the pineal gland? Light exposure to the retina is first relayed to the
suprachiasmatic nucleus of the hypothalamus, an area of the brain well
known to coordinate biological clock signals. Fibers from the
hypothalamus descend to the spinal cord and ultimately project to the
superior cervical ganglia, from which post-ganglionic neurons ascend
back to the pineal gland. Thus, the pineal is similar to the adrenal
medulla in the sense that it transduces signals from the sympathetic
nervous system into a hormonal signal.
http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/pineal.html
