Chapter 17: Special Senses (Vision) Flashcards
the act of seeing, is extremely important to human
survival because it allows us to view potentially
dangerous objects in our surroundings.
More than half the sensory receptors in the human
body are located in the eyes, and a large part of the
cerebral cortex is devoted to processing visual
information.
VISION
is the science that deals with the eyes and their
disorders
OPTHAMOLOGY
is energy in the form of waves that radiates from the
sun. There are many types of electromagnetic
radiation, including gamma rays, x-rays, UV rays,
visible light, infrared radiation, microwaves, and radio
waves.
ELECTROMAGNETIC RADIATION
CTROMAGNETIC SPECTRUM
This range of _____________
The distance between two consecutive peaks of an
electromagnetic wave is the wavelength.
Wavelengths range from short to long; for example,
gamma rays have wavelengths smaller than a
nanometer, and most radio waves have wavelengths
greater than a meter
electromagnetic radiation
include the eyelids, eyelashes, eyebrows, the
lacrimal (tear-producing) apparatus, and extrinsic
eye muscles.
ACCESSORY STRUCTURES OF THE EYE
The upper and lower eyelids, or palpebrae
(singular: palpebral)
o shade the eyes during sleep, protect the
eyes from excessive light and foreign objects, and spread lubricating secretions
over the eyeballs.
EYELIDS
more movable than the lower and contains
in its superior region the levator palpebrae
superioris.
Upper Eyelid
more movable than the lower and contains
in its superior region the levator palpebrae
superiori
Palpebral Fissure
narrower and closer to the temporal bone,
Lateral Commissure
o broader and nearer the nasal bone. In the
_______ is a small, reddish
elevation
Medial Commissure
which contains sebaceous (oil) glands and
sudoriferous (sweat) glands. The whitish
material that sometimes collects in the
medial commissure comes from these
glands.
Lacrimal Caruncle
o thick fold of connective tissue that gives
form and support to the eyelids
Tarsal Plate
Embedded in each tarsal plate is a row of
elongated modified sebaceous glands
o Or Meibomian glands
o secrete a fluid that helps keep the eyelids
from adhering to each other
Tarsal Glands
Infection of the tarsal glands produces a
tumor or cyst on the eyelid
Chalazion
is a thin, protective mucous membrane
composed of nonkeratinized stratified
squamous epithelium with numerous goblet
cells that is supported by areolar connective
tissue
Conjunctiva
lines the inner aspect of the eyelids
Palpebral Conjunctiva
passes from the eyelids onto the surface of
the eyeball, where it covers the sclera (the
“white” of the eye) but not the cornea, which
is a transparent region that forms the outer
anterior surface of the eyeball.
Bulbar Conjunctiva
which project from the border of each eyelid
Eyelashes
which arch transversely above the upper
eyelids, help protect the eyeballs from
foreign objects, perspiration, and the direct
rays of the sun
Eyebrows
Sebaceous glands at the base of the hair
follicles of the eyelashes
o release a lubricating fluid into the follicles
Sebaceous Ciliary Glands
Infection of these glands, usually by
bacteria, causes a painful, pus-filled
swelling
Sty
a group of structures that produces and drains
lacrimal fluid or tears in a process called
lacrimation.
THE LACRIMAL APPARATUS
each about the size and shape of an
almond, secrete lacrimal fluid, which drains
into 6–12 excretory lacrimal ducts
Lacrimal Glands
empty tears onto the surface of the
conjunctiva of the upper lid.
Excretory Lacrimal Ducts
o (singular: punctum)
o From here the tears pass medially over the
anterior surface of the eyeball to enter two
small openings
o Tears then pass into two ducts, the superior
and inferior lacrimal canaliculi, which lead
into the lacrimal sac (within the lacrimal
fossa) and then into the nasolacrimal duct.
Lacrimal Puncta
This duct carries the lacrimal fluid into the
nasal cavity just inferior to the inferior nasal
concha where it mixes with mucus.
Nasolacrimal ducts
An infection of the lacrimal sacs.
Dacryocystitis
The adult eyeball measures about 2.5 cm (1 in.) in
diameter
Anatomically, the wall of the eyeball consists of three
layers
(1) fibrous tunic, (2) vascular tunic, and (3)
retina (inner tunic).
the superficial layer of the eyeball and
consists of the anterior cornea and posterior
sclera.
FIBROUS TUNIC
a transparent coat that covers the colored
iris
Cornea
the “white” of the eye, is a layer of dense
connective tissue made up mostly of
collagen fibers and fibroblasts
o The sclera covers the entire eyeball except
the cornea; it gives shape to the eyeball,
makes it more rigid, protects its inner parts,
and serves as a site of attachment for the
extrinsic eye muscles
Sclera
or (canal of Schlemm). A fluid called
aqueous humor, which will be described
later, drains into this sinus
Scleral Venous Sinus
Or uvea is the middle layer of the eyeball. It
is composed of three parts: choroid, ciliary
body, and iris
VASCULAR TUNIC
the posterior portion of the vascular tunic,
lines most of the internal surface of the
sclera.
o Its numerous blood vessels provide
nutrients to the posterior surface of the
retina. The choroid also contains
melanocytes that produce the pigment
melanin, which causes this layer to appear
dark brown in color. Melanin in the choroid
absorbs stray light rays, which prevents
reflection and scattering of light within the
eyeball.
Choroid
In the anterior portion of the vascular tunic,
the choroid becomes the ciliary bod. It
extends from the ora serrata
Ciliary Blood
o the jagged anterior margin of the retina, to
a point just posterior to the junction of the
sclera and cornea
Ora Serrata
are protrusions or folds on the internal
surface of the ciliary body. They contain
blood capillaries that secrete aqueous
humor
Ciliary Processes
Extending from the ciliary process
o or suspensory ligaments that attach to the
lens.
Zonular Fibers
a circular band of smooth muscle.
Contraction or relaxation of the ciliary
muscle changes the tightness of the zonular
fibers, which alters the shape of the lens,
adapting it for near or far vision.
Ciliary Muscles
the colored portion of the eyeball, is shaped
like a flattened donut. It is suspended
between the cornea and the lens and is
attached at its outer margin to the ciliary
processes
Iris
o the hole in the center of the iris. The pupil
appears black because, as you look
through the lens, you see the heavily
pigmented back of the eye (choroid and
retina)
Pupil
or sphincter pupillae
o causing a decrease in the size of the pupil
(constriction).
Circular muscles
or dilator pupillae of the iris to contract,
causing an increase in the pupil’s size
(dilation).
Radial Muscles
The third and inner layer of the eyeball
lines the posterior three-quarters of the eyeball and
is the beginning of the visual pathway
RETINA
is the site where the optic (II) nerve exits
the eyeball.
Optic Disc
a branch of the ophthalmic artery
Central Retinal Artery
o Branches of the central retinal artery fan
out to nourish the anterior surface of the
retina; the central retinal vein drains blood
from the retina through the optic disc
The retina consists of a pigmented layer and a neural
layer
Central Retinal Vein
a sheet of melanin-containing epithelial
cells located between the choroid and the
neural part of the retina.
Pigmented Layer
a multilayered outgrowth of the brain that
processes visual data extensively before
sending nerve impulses into axons that
form the optic nerve.
Neural (sensory) Layer
the photoreceptor cell layer, the bipolar
cell layer, and the ganglion cell layer- are
separated by two zones, the outer and inner
synaptic layers, where synaptic contacts
are made
Three distinct of retinal neurons
Two other types of cells present in the
bipolar cell layer of the retina
o These cells form laterally directed neural
circuits that modify the signals being
transmitted along the pathway from
photoreceptors to bipolar cells to ganglion
cells.
Horizontal cells and Amacrine cells
o allow us to see in dim light, such as
moonlight. Because rods do not provide
color vision, in dim light we can see only
black, white, and all shades of gray in
between.
Rods
Brighter lights stimulate
o produce color vision. Three types of cones
are present in the retina: (1) blue cones,
which are sensitive to blue light, (2) green
cones, which are sensitive to green light,
and (3) red cones, which are sensitive to
red light.
Cones
also called the blind spot
Optic Disc
or yellow spot is in the exact center of the
posterior portion of the retina, at the visual
axis of the eye.
Macula lutea
a small depression in the center of the
macula lutea, contains only cones.
Fovea Centralis
Behind the pupil and iris, within the cavity of the
eyeball
LENS
arranged like the layers of an onion, make
up the refractive media of the lens, which
normally is perfectly transparent and lacks
blood vessels
Crystallins
The lens divides the interior of the eyeball into two
cavities: the anterior cavity and vitreous chamber.
INFERIOR OF THE EYEBALL
the space anterior to the lensconsists of two
chambers
Anterior Cavity
o lies between the cornea and the iris
Anterior Chamber
o lies behind the iris and in front of the zonular
fibers and lens
Posterior chamber
o a transparent watery fluid that nourishes the
lens and cornea.
Acqueous Humor
which lies between the lens and the retina
Vitreous Chamber
a transparent jellylike substance that holds
the retina flush against the choroid, giving
the retina an even surface for the reception
of clear images
Vitreous Body
a narrow channel that is inconspicuous in
adults and runs through the vitreous body
from the optic disc to the posterior aspect of
the lens.
Hyaloid Canal
The pressure in the eye
o produced mainly by the aqueous humor and
partly by the vitreous body; normally it is
about 16 mmHg (millimeters of mercury
Intraocular Pressure
This increase in the curvature of the lens for
near vision
o The near point of vision is the minimum
distance from the eye that an object can be
clearly focused with maximum
accommodation. This distance is about 10
cm (4 in.) in a young adult.
Accommodation
is a narrowing of the diameter of the hole
through which light enters the eye due to
the contraction of the circular muscles of the
iris.
Constriction of the Pupil
o provide output from the retina to the brain.
Optic (II) Nerve
a crossing point of the optic nerves
Optic Chiasm
After passing through the optic chiasm, the
axons, now part of the optic tract, enter the
brain and most of them terminate in the
lateral geniculate nucleus of the
thalamus.
Optic Tract
they synapse with neurons whose axons
form the optic radiations
Lateral Geniculate Nucleus
project to the primary visual areas in the
occipital lobes of the cerebral cortex
Optic radiations
visual perception begins
Primary Visual Areas
which control the extrinsic eye muscles
Super Colliculi
which control pupillary and accommodation
reflexes.
Pretectal Nuclei
o Everything that can be seen by one eye is
that eye’s ________
visual field.
