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what are three layers of the eye?

fibrous, vascular and sensory

what layer of the eye carries out the eye function?

the sensory layer

what part of the eye focuses?

the lens

what separates the anterior and posterior parts of the eye?

the lens

the five special senses


five special senses all have..

specialized sensory receptors inside sensory organs or epithelial structure


receptor that provides information about the external environment
found in all special senses


the dominant sense in humans

size of an adult human eye


amount of eye exposed in humans

1/6 of anterior

lacrimal apparatus

contains the lacrimal glands and ducts

lacrimal glands

located at the superiolateral corner of eye
produces tears


saline-like with mucus, antibodies, and lysozyme

pathway of tears

enter superiolaterally and exit medially, then drain into nasal cavity

function of eye muscles

move the eye
maintain eye shape
hold in place

extrinsic eye muscles

superior rectus
inferior rectus
medial rectus
lateral rectus
superior oblique
inferior oblique

superior rectus

elevates eye and turns medially

inferior rectus

depresses eye and turns medially

medial rectus

moves eye medially

lateral rectus

moves eye laterally

superior oblique

depresses eye and turns laterally

inferior oblique

elevates eye and turns laterally

muscles that move the eye laterally

lateral rectus
superior oblique
inferior oblique

muscles that move the eye medially

superior rectus
medial rectus
medial rectus


fill the internal cavity of the eye
maintain shape

aqueous humor

watery substance that fills the anterior chamber
supports, nourishes and removes waste

vitreous humor

gel-like substance in posterior chamber of eye
supports lens and holds retina in place
creates pressure to offset pulling of extrinsic muscles

how long does vitreous humor last?

a life time; it forms in embryo


when aqueous humor is made faster than drained

composition of the fibrous layer

made of avascular dense connective tissue

posterior portion of fibrous layer in eye

opaque and white schlera


white off the eye
made of fibrous connective tissue
(posterior end is pierced by optic nerve)

function of sclera

protects eye and anchors extrinsic muscles

anterior part of fibrous layer

made of cornea


anterior part of fibrous layer
allows light to enter the eye
contains lots of touch and pain receptors

what part of the eye contains epithelial cells that renew regularly?

the cornea

when cornea is touched...

...eye will blink automatically

what part of the eye can be transplanted? why?

cornea, because it contains no blood vessels

choroid region

posterior 5/6 of vascular layer in eye
supplies blood to all eye layers
contains melanin to prevent light scattering

ciliary body

anterior 1/6 of vascular layer in eye
a thickened ring of tissue surrounding lens
ciliary muscles
ciliary zonule
ciliary process

ciliary muscles

control shape of lens
part of the ciliary body

ciliary zonule

ligament holding lens in place

ciliary process

radiating folds near lens
secretes aqueous humor

what determines the color of the iris?



central opening of the iris
part of the vascular layer

what regulates amount of light entering the eye?

the pupil

in close vision and bright light the pupil will...


in distant vision and dim light the pupil will...


another name for the sensory layer

the retina

two layers of the retina

pigmented layer
neural layer

pigmented layer in the retina

absorbs and prevents light from scattering

neural layer in the retina

contains photoreceptors and blood vessels

what layer in the eye responses to light?

neural layer of the retina

optic disc

where the optic nerve leaves the eye

why does the optic disc create a blind spot?

there are no photoreceptors on the optic nerve

fovea centralis

contains only cones and has highest visual acuity


cones and rods


bright light receptors
produce high-acuity color vision

what colored cones do humans have?

blue, green and red
all respond to different lights

what causes colorblindness?

a lack of one or more cones types
is genetic


dim light and peripheral vision receptors
sensitivity to light
produce black and white images

which are more common? rods or cones?

rods are more common

structure of the lens

biconvex and flexible


lens becomes dense and less elastic with age

what causes near point of accommodation to increase?



lens becomes cloudy with age
(can be surgically replaced)

pathway of an image

light -> cornea -> aqueous humor -> lens -> vitreous humor -> retina -> photoreceptors -> optic nerve -> cerebral cortex

how is an image flipped through pathway?

up-side-down and right-and-left reversed

what "corrects" a flipped image?

cerebral cortex

emmetropic eye

normal eye with proper focus

myopic eye

nearsighted (can not see far well)

hyperopic eye

farsighted (can not see close well)

chemical senses

gustation and olfaction

chemoreceptors respond to what?

chemicals in aqueous solution
taste - dissolved in saliva
smell - dissolved in nasal mucus

olfactory epithelium

organ of smell
located on the roof of the nasal cavity

olfactory receptors

located on the olfactory epithelium
bipolar neurons
each with dendrite with several olfactory cilia

supporting cells

secrete mucus
surround olfactory receptors

olfactory cilia

extend from dendrites of bipolar olfactory receptors
increase receptive surface area

what is formed by the axons of olfactory receptors?

olfactory nerve

smell stimulates what parts of the brain?

olfactory cortex for interpretation
thalamus for emotional response

if a smell if associated with danger, it will trigger the...

...sympathetic nervous response

if a smell is appetizing...

...saliva will be secreted

if a smell is unpleasant...

...sneezing and coughing reflexes are triggered

organs for taste

taste buds

tongue papille

peg-like projections of the tongue mucosa
where taste buds can be found

types of tongue papille


what is the least functional tongue papille?

foliate (though more active in kids)

what is the most numerous tongue papille?


what is the largest tongue papille?


how many gustatory and basal cells does a taste bud have?


gustatory hairs

extend through taste pore to the epithelial surface

in the mouth, basal cells...

differentiate into new gustatory cells
(stem cells)

how many different smells do humans have?

10, 000
(500 proteins deposited on receptor cells)

five basics tastes


part of the brain that is stimulated by taste

gustatory cortex for recognition
hypothalamus for appreciation (emotional response)

cranial nerves associated with taste

facial - anterior 2/3 tongue
glossopharyngeal - posterior 1/3 tongue
vagus - epiglottis and pharynx

how many different tastes do humans have?


what percentage of taste is actually smell?


what parts of the ear are involved in hearing?

outer and middle parts

what part of the ear is involved in hearing and equilibrium?

inner ear

differences between hearing and equilbrium

have two different receptors
receptors respond to different stimuli
activated independently

parts of the outer ear

auricle and external acoustic meatus
tympanic membrane


outer ear
supported by elastic cartilage
helix and lobule

helix of ear

rim of the outside
part of the auricle



external acoustic meatus

curved tube on the temporal bone
filled with hair, sebaceous glands and ceruminous glands

tympanic membrane

thin, translucent connective tissue membrane
vibrates in response to sound
transfers sounds to middle ear bones

what divides the outer and middle ears?

tympanic membrane

what two openings connect the middle ear with the inner ear?

superior oval window
inferior round window

middle ear

small, air filled, mucosa-lined cavity

superior oval window

connects middle ear to vestibule

inferior round window

connects middle ear to cochlea

auditory tube

connects middle ear to pharynx
usually flattened and closed, opens when yawning

what equalizes middle ear pressure with external air?

auditory tube

bones of the middle ear (ossicles)

malleus, incus and stapes

what transmits eardrum vibrations to the inner ear?

malleus, incus and stapes

vibration of very loud sounds is dampened by...

...two small muscles????

where is the inner located?

deep in temporal bone and behind the eye socket

what is the most complex part of the ear?

the inner ear

bony labyrinth

channels within the bone
vestibule, semicircular canals and cochlea
filled with perilymph


fills the bony labyrinth

membranous labyrinth

membrane sacs within the bony labyrinth
suspended in perilymph
filled with endolymph

what do the fluids of the inner ear do?

conduct sound vibrations (hearing)
respond to mechanical forces during position change (equilibrium)

what is the central cavity of the bony labyrinth?

the vestibule


contains saccule and utricle
houses equilbrium receptors


smaller sac of the vestibule
extends into the cochlea


larger sac of the vestibule
extends into the semicircular canals

equilibrium receptors

respond to gravity and changes in head position

semicircular canals

three canals that define 2/3 of a circle and lie in three planes of space
(90 degrees from each other)

membranous semicircular ducts

line each canal and communicate with the utricle

what part of the semicircular canals house equilibrium receptors?

the swollen ends of the canal

what responds to angular movements of the head?

swollen ends of the semicircular canals


houses hearing receptors spiral organs of corti
spiral bony chamber extending from vestibule
houses cochlear duct that ends at cochlear apex

how many turns does the cochlea take?

about 2.5

what is the dead end of the cochlea?

the cochlear apex

transmission of sound

outer ear (pinna and auditory canal)
tympanic membrane
middle ear bones
oval window
inner ear
cochlear duct
organ of corti
hair cell bending
basilar membrane
action potential in cochlear nerve
nerve cerebral cortex

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