Regulation and Integration of the Body
becomes the retina. Overlying ectoderm folds to form the lens
vesicle, which gives rise to the lens. Te remaining eye tissues and
the accessory structures are formed by mesenchyme.
Te eye is foreshortened at birth and reaches adult size at the age of
8–9 years. Depth perception and color vision develop before age 3.
With age, the lens loses its elasticity and clarity, there is a decline
in the ability of the iris to dilate, and visual acuity decreases. Te
elderly are at risk for eye problems resulting from dry eyes and
Hearing and Balance
Te membranous labyrinth develops from the otic placode, an
ectodermal thickening lateral to the hindbrain. Mesenchyme
forms the surrounding bony structures. Pharyngeal pouch
endoderm, in conjunction with mesenchyme, forms most
middle ear structures; the external ear is formed largely by
Congenital ear problems are fairly common. Maternal rubella can
Response to sound in infants is reﬂexive. By the fourth month, an
infant can locate sound. Critical listening develops in toddlers.
Te spiral organ deteriorates throughout life as noise, disease,
and drugs destroy cochlear hair cells. Age-related loss of hearing
(presbycusis) occurs in the 60s and 70s.
the cerebellum. Tese centers initiate responses that ﬁx the eyes
on objects and activate muscles to maintain balance.
Homeostatic Imbalances of Hearing and Equilibrium
Conduction deafness results from interference with conduction
of sound vibrations to the ﬂuids of the internal ear. Sensorineural
deafness reﬂects damage to neural structures.
±innitus is an early sign of sensorineural deafness; it may also
result from inﬂammation or certain drugs.
Ménière’s syndrome is a disorder of the membranous labyrinth.
Symptoms include tinnitus, deafness, and vertigo. Excessive
endolymph accumulation is the suspected cause.
Developmental Aspects of the Special Senses
Taste and Smell
Te chemical senses are sharpest at birth and gradually decline
with age as receptor cells are replaced more slowly.
Congenital eye problems are uncommon, but maternal rubella
can cause blindness.
Te eye starts as an optic vesicle, an outpocketing of the
diencephalon that invaginates to form the optic cup, which
(Some questions have more than one correct answer. Select the best
answer or answers from the choices given.)
Accessory glands that produce an oily secretion are the
Te portion of the ﬁbrous layer that is white and opaque is the
Which sequence best describes a normal route for the ﬂow of
tears from the eyes into the nasal cavity?
lacrimal sacs, nasolacrimal ducts;
lacrimal ducts, lacrimal
canaliculi, nasolacrimal ducts;
nasolacrimal ducts, lacrimal
canaliculi, lacrimal sacs.
Activation of the sympathetic nervous system causes
contraction of the sphincter pupillae muscles,
of the dilator pupillae muscles,
contraction of the ciliary
a decrease in ciliary zonule tension.
Damage to the medial recti muscles would probably aﬀect
Te phenomenon of dark adaptation is best explained by the fact
rhodopsin does not function in dim light,
breakdown occurs slowly,
rods exposed to intense light need
time to generate rhodopsin,
cones are stimulated to function
by bright light.
Blockage of the scleral venous sinus might result in
Nearsightedness is more properly called
Of the neurons in the retina, the axons of which of these form the
Which sequence of reactions occurs when a person looks at a
pupils constrict, ciliary zonule (suspensory
ligament) relaxes, lenses become less convex;
ciliary zonule becomes taut, lenses become less convex;
dilate, ciliary zonule becomes taut, lenses become more convex;
pupils constrict, ciliary zonule relaxes, lenses become more
During embryonic development, the lens of the eye forms
as part of the choroid coat,
from the surface ectoderm
overlying the optic cup,
as part of the sclera,
Te blind spot of the eye is
where more rods than cones are
where the macula lutea is located,
where only cones
where the optic nerve leaves the eye.
Olfactory tract damage would probably aﬀect your ability to
Sensory impulses transmitted over the facial, glossopharyngeal,
and vagus nerves are involved in the sensation of
±aste buds are found on the
anterior part of the tongue,
posterior part of the tongue,
all of these.
Gustatory epithelial cells are stimulated by
substances in solution,
Cells in the olfactory bulb that act as local “integrators” of
olfactory inputs are the
amacrine granule cells,
olfactory stem cells,
Olfactory nerve ﬁlaments are found
in the optic bulbs,
passing through the cribriform plate of the ethmoid bone,
in the optic tracts,
in the olfactory cortex.
Conduction of sound from the middle ear to the internal ear
occurs via vibration of the
malleus against the tympanic