Mice who are totally blind (lacking both rods and cones) have no
trouble keeping their circadian clock on time. This is common to all
mammals.

They are able to do this because some 1--2% of the ganglion cells in
their retina -- instead of depending on signals arriving from rods
and/or cones -- detect light directly.

These ganglion cells have an extensive network of dendrites that
contain the pigment Melanopsin. When exposed to light (diffuse light is
fine), these ganglion cells become depolarized and send their signals
back to the Suprachiasmatic nucleus (SCN). The SCN sends information
to other hypothalamic nuclei and the pineal gland to modulate body
temperature and production of hormones such as cortisol and melatonin.

If the eyes were to be nonexistent or more severely damaged then this
of course could not happen.

Tony, Suki and Sweetie.
In memory of Sally, Sue and Sugar.

[Posted in FML 7515]