Lesson 2 - Part 2 - Special Senses Flashcards
vision (sight)
perception of objects in the environment by means of light they emit or reflect
light
visible part of the electromagnetic spectrum
light must cause a _____ reaction to produce a nerve signal
photochemical
ultraviolet radiation
< 400nm, has too much energy and destroys macromolecules
infrared (IR) radiation
> 700 nm, too little energy to cause photochemical reaction, but does warm the tissues
orbital region
area around the orbit (eye socket), contain structures that protect and aid the eye
eyebrows
enhance facial expression, protect eyes from glare and perspiration
eyelids (palpebrae)
consist of orbicularis oculi muscle and supportive fibrous tarsal plate
medial and lateral commissures
where the eyelids meet on the medial and lateral sides of the eyes
eyelids are covered with _____ outside and _____ inside
skin, conjunctiva
tarsal glands
secrete oil that reduces tear evaporation and prevents the eyelids from sticking together
eyelashes help….
keep debris out of the eye
conjunctiva
transparent mucous membrane lining the eyelids and covering the anterior eyeball, expect the cornea
conjunctivitis
pinkeye, inflammation and associated redness caused by allergic reaction, chemical irritations, or an infection by a pathogen
what does the conjunctiva do?
secretes a thin mucous film to prevent the drying of the eyeball
lacrimal apparatus
gland and tear ducts for production and drainage of tears
lacrimal gland
in superolateral corner of the orbit, it secretes tears
tears
slightly alkaline, watery secretion containing antibodies and bactericidal lysozyme; washes over and lubricates the eye, delivers oxygen and nutrients to conjunctiva
lacrimal punctum
opening on the eyelid edge
how do tears flow through the eye? (4)
- lacrimal punctum
- lacrimal sac
- nasolacrimal duct
- empty into the nasal cavity
lacrimal caruncle
mass of soft tissue containing glands that produce a thick secretion that forms into a gritty deposit (you discover after waking up)
orbital fat
cushions the eye, protects vessels and nerves
extrinsic eye muscles
attach to exterior surface of the eye
rectus muscles
superior, inferior, medial, and lateral rectus
oblique muscles
superior and inferior
all of the extrinsic eye muscles (6)
- superior rectus
- inferior rectus
- medial rectus
- lateral rectus
- superior oblique
- inferior oblique
what cranial nerves innervate the extrinsic eye muscles? What muscles do they innervate? (3)
- IV innervates superior oblique
- VI innervates lateral rectus
- III innervates other four extrinsic muscle
how does the superior rectus move the eyeball?
up
how does the inferior rectus move the eyeball?
down
how does the medial rectus move the eyeball?
medially
how does the lateral rectus move the eyeball?
laterally
how do the superior and inferior obliques turn the eye?
turns the 12 o’clock pole of each eye toward or away from the nose; they also produce slight elevations and depressions of the eye
three tunics of the eye
- fibrous layer
- vascular layer
- inner layer
fibrous layer of the eye (3)
outer layer derived from two regions
- sclera
- cornea
- corneal limbus
vascular layer of the eye
uvea; middle layer with three regions
- choroid
- ciliary body
- iris
how does the ciliary body support the eye?
it supports the lens and iris by secreting aqueous humor
how does the pupil dilate?
dilation of the pupil caused by sympathetic stimulation of pupillary dilator muscle
how does the pupil constrict?
constriction of the pupil is caused by the parasympathetic stimulation of the pupillary constrictor muscles
what causes a dark iris?
a lot of melanin in chromatophores
chromatophores
iris pigmented cells
choroid
highly vascular, darkly pigmented layer behind the retina that provides oxygen and nutrients to the retina
ciliary body
extension of the choroid, a muscular ring around the lens
iris
colored diaphragm controlling the size of the pupil
functions of the uvea (4)
- provides route for blood/lymphatic vessels that supply the eye
- regulates amount of light entering the eye
- secretes and reabsorbs aqueous humor that circulate within the anterior cavity of the eye
- controls the shape of the lens to focus light onto the retina
sclera
tough, fibrous protective layer; the white of the eye
cornea
anterior transparent region; admits light into the eye
corneal limbus
border separating the sclera from the cornea
inner layer of the eye
retina and pigmented epithelium located next to choroid of the uvea
what does the pigmented epithelium do?
absorbs light that passes through the inner neural layer and prevents light from bouncing back into the retina
the inner layer contains what specialized cells?
photoreceptors called rods and cones
rods
do not detect different wavelengths (cannot detect colors); however, very sensitive to light, used in low light surroundings
cones
provides color vision; cones clustered at fovea centralis at the center of the macula lutea
cornea
transparent window allowing light into the eye, the initial refraction of light occurs here
aqueous humor
serous fluid secreted by ciliary body into the posterior chamber between the iris and lens
posterior chamber of the eye
the area between the iris and the lens
anterior chamber of the eye
the space between the iris of the cornea
scleral venous sinus
reabsorbs aqueous humor at the same rate at which it is secreted
where are the anterior and posterior chambers located?
located in the anterior cavity of the eye
lens
transparent structure composed of flattened compressed transparent cells called lens fibers
suspensory ligament
the ligament connected to the ciliary muscles of the ciliary body
what does contraction of the ciliary muscle do?
loosens the suspensory ligament and causes lens to become thicker/rounder to focus near objects
what does relaxation of ciliary muscle do?
muscle tightens the suspensory ligament and causes lens to flatten to focus on far objects
vitreous body
gelatinous substance that fills the vitreous chamber (posterior cavity) located behind lens
what does the vitreous body maintain?
intraocular pressure; helps hold the retina against the wall of the eye and blood supply
what are lens fibers filled with?
crystallins, which provides transparency to the lens
cataracts
clouding of the lenses
cataracts consists of….
- lens fibers darken with age
- fluid filled bubbles and clefts filled with debris appear between the fibers
treatment for cataracts
replacing natural lens with plastic one
what can cataracts be induced by? (5)
- diabetes
- smoking
- drugs
- ultraviolet radiation
- certain viruses
glaucoma
pressure within the eye due to obstruction of scleral venous sinus causing improper drainage of aqueous humor and increased intraocular pressure
what does glaucoma cause?
this causes compression of blood vessels and lack of oxygen and death of retinal cells (peripheral vision is first affected)
macular degeneration
death of photoreceptor cells in macula lutea (central part of the retina)
what does macular degeneration cause?
loss of vision in the center of visual field
can macular degeneration be cured?
no, but its progression can be slowed
diabetic retinopathy
retinal degeneration caused by effects of diabetes mellitus; causes blockage of normal retinal blood vessels and growth of abnormal vessels and blood leakage into the posterior cavity
what causes the most cases of adult blindness in the US?
diabetic retinopathy
optic disc
medial to macula lutea where the ganglion cell axons converge and leave the eye as the optic nerve
blind spot
the optic disc where no photoreceptor cells are located
visual filling
brain fills in the blind spot area
scotomas
abnormal blind spots (blind spots in areas in other than the optic disc)
causes of scotomas (3)
- compression of optic disc
- damage to photoreceptors
- damage to the visual pathway
visual process
light enter the eye, focused on the retina, and produces a tiny inverted image
what two sets of contractile elements control iris diameter?
- pupillary constrictor
- pupillary dilator
pupillary constrictor
smooth muscle encircling the pupil
parasympathetic stimulation to the pupillary constrictor does what?
narrows the pupil
sympathetic stimulation to the pupillary dilator does what?
widens the pupil
pupillary dilator
spoke-like myoepithelial cells located distal to the pupil compared to pupillary constrictor muscle
what do pupil constriction and dilation occur in response to? (3)
- emotions
- changes in light intensity
- when gaze shifts between distant and nearby objects
photopupillary reflex
pupillary constriction in response to light
refraction
bending of light =
refractive light index
of a medium; how much a substance retards light rays
the _____ refracts light more than the _____
cornea, lens
astigmatism
condition where light passing through the cornea and lens is not refracted properly causing visual distortions
emmetropia
normal vision where the eye is relaxed and focused on object more than 20ft away
near response
adjustment to close-range vision
three steps of near response
- convergence of eye
- constriction of pupils
- accommodation of lenses
near response: convergence of the eyes
eyes orient their visual axis
near response: constriction (miosis) of the pupil
blocks peripheral light rays and reduces spherical aberration
spherical aberration
blurry edges
near response: accommodation of the lens (3)
change in the curvature of the lens
- ciliary muscles contract, suspensory ligaments slacken, and lens takes more convex shape
- light is refracted more strongly and focused onto the retina
hyperopia
farsightedness; far objects appear clear, but nearby objects are blurry
presbyopia
age-related hyperopia in adults 40+
myopia
nearsightedness; nearby objects appear clear but far objects are blurry
pigmented layer (pigmented apithelium)
most posterior part of retina; absorbs stray light so visual image is not degraded
neural components of the retina: photoreceptor cells
rods, cones, and certain ganglion cells
photoreceptor cells
absorb light and generate a chemical electrical signal, but are not neurons
bipolar cells
synapse with rods and cones, serve as first-order neurons that carry signal to ganglino cells
ganglion cells
second-order neurons of the visual pathway; their axons form the optic nerve
outer segment of rods and cones
points toward the wall of the eye, towards the pigmented layer, and contains modified cilium specialized to absorb light
inner segment of rods and cones
facing the interior of the eye; contains organelles and gives rise to cell body and process that form synapse
rods
responsible for night (scotopic) vision, produces images in shades of grey
monochromatic vision
images produced by rods are in shades of grey
rhodopsin
the visual pigment in the outer segment of rods
cone
responsible for day (photopic) vision and color (trichromatic) vision
the outer segment of cones contain discs that are plasma membrane infolding that contain…
pigments for light absorption
where do rods and cones continually renew their discs?
new ones add to the proximal (basal) end of the outer segment, old discs shed from the distal tips of the cells and are phagocytized in the pigment epithelium
horizontal cells
don’t form separate layers in the retina; modulates information from photoreceptors to bipolar cells
amacrine cells
don’t form separate layers in the retina; modulates information from bipolar cells to ganglion cells
neural convergence
multiple rods or cones synapse on one bipolar cells and multiple bipolar cells synapse on one ganglion cell
retinitis pigmentosa
most common inherited visual problem; caused by a mutation in a visual pigment that results in photoreceptor cells death, and ultimately blindness
two major parts of rhodopsin
- opsin protein and retinene (retinal) derived from vitamin A
where is opsin in rods?
embedded in disc membranes of the outer segment
nyctalopia
night blindness, can be caused by a dietary vitamin A deficiency
all rods contain a single kind of rhodopsin that _____ distinguish color
cannot
cones contain a pigment called
photopsin
the different parts of opsin in cones contain
different amino acid sequences that determine wavelengths of light absorbed
three types of cones
red, green, blue
how do red, green, and blue differ?
each type expresses a different type of opsin, therefore absorbs slightly different wavelengths of light
how does the brain determine color?
it compares the response levels across all three types of cones to determine color
light adaptation
adjustment in vision when moving from a dark or dim area into brighter light
what is the time needed for pigment bleaching to adjust retinal sensitivity to high light intensity?
5 to 10 minutes
dark adaptation
adjustment to vision when moving from a bright area into a dark or dim area
how long does it take for night vision to start working?
1-2 minutes
when does night vision reach peak sensitivity?
20-30 minutes
duplicity theory of vision
a single receptor system cannot produce both high sensitivity and high resolution; explains why we need rods and cones
spatial summation
onge ganglion cell receives info from 1mm^2 of retina producing only a coarse image
edges of the retina have widely spaced rods that act as
motion detectors; low-resolution systems only, cannot resolve finely detailed images
what happens to rods when light is bright enough to have color vision?
rods are photobleached and not contributing to vision
the fovea has no, what?
no neuronal convergence, each cone has its “private line to the brain”
color blindness
hereditary alteration of lack or one photopsin or another
red-green color blindness
results from a lack of either red or green cones since the individual has difficulty distinguishing shades of red and green
stereoscopic vision (stereopsis)
depth perception, the ability to judge distance to objects
what does stereoscopic vision require?
two eyes with overlapping visual fields which allows each eye to look at the same object from different angles
fixation point
point in space which the eyes are focused
first-order neurons of the retina
bipolar cells
second-order neurons of the retina
retinal ganglion cells
axons exiting the back of each eye leave the eye as which nerve?
the optic nerve, CN II
hemidecussation
half the fibers from each optic nerve cross over at the optic chiasm
optic tracts
fibers come together after the chiasm to form the right and left of these
the optic tracts pass laterally around the hypothalamus with most of their axons ending where?
lateral geniculate nucleus of the thalamus
third-order neurons arise and form the _____ _____ of fibers in the white matter of the cerebrum
optic radiation
what does the optic radiation do?
project to the primary visual cortex of the occipital lobe where conscious visual sensation occurs
where do some fibers of the optic radiation project? why?
hypothalamus to affect circadian rhythm
a few optic nerve fibers project to the midbrain and terminate in the _____ _____ and _____ _____
superior colliculi and pretectal nuclei
what does the superior colliculi control?
controls the visual reflexes and extrinsic eye muscles
what are the pretectal nuclei involved in?
photopupillary and accommodation reflexes
