caused by congenital factors, excess ultraviolet (UV) radiation, or high glu-
cose levels.
Thechoroidandscleraare the supportive, protective coats of the eye.
Theaqueous humor,produced by processes of the ciliary body, flows
between the lens and iris to the anterior chamber of the eye toward the iri-
docorneal angle,where it is drained into the canal of Schlemm.Blockage
of the canal of Schlemm or associated structures leads to increased
intraocular pressureandglaucoma.
EARThe ear functions in two separate but related signal transduction systems,
auditionandequilibrium.Theexternal ear,largely formed from the first
two branchial arches,funnels sound to the tympanic membrane.The
middle earis made up of the malleus, incus, and stapesformed from the
first two arch cartilages.Theinternal earconsists of a membranousand
abony labyrinthfilled with endolymphandperilymph,respectively. The
saccule (ventral) and utricle (dorsal), parts of the membranous
labyrinth, form from the otic vesicle(an ectodermal invagination). The
cochleacontains three spaces, the scala vestibuli, scala media(cochlear
duct,which extends from the saccule), and scala tympani.Thesemicircu-
lar canals(which extend from the utricle) contain the cristae ampulares,
made up of cupulaewithhair cellsembedded in a gelatinous matrix that
respond to changes in directionandrate of angular acceleration.The
hair cells are located within the organ of Cortiand respond to different
frequencies.In the sacculeandutricle,themaculae,along with stere-
ocilia, kinocilia,andotoconia(crystals of protein and calcium carbonate),
detectchanges in positionwith reference to gravity.
High-Yield Facts 37