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what are your special senses?
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smell, taste, sight, hearing, equilibrium
what are your special sense receptors?
large, complex sensory organs (eye and ear)
localized clusters of receptors (taste buds and olfactory epithelium)
how many receptors are in the eye?
70% of all sensory receptors are in the eye
what are the accessory structures of the eye?
extrinsic eye muscles, eyelids, conjunctiva, lacrimal apparatus
opens and closes to protect the eye
meet at medial and lateral commissure (canthus)
glands secrete different lubricants to moisture and protect eye
2 types of glands
produce an oily secretion that lubricates the eye
located between the eyelashes
membrane that lines the eyelid and eyeball
connects with the transparent cornea
secretes mucus to lubricate the eye and keep it moist
lacrimal gland and ducts
produces lacrimal fluid
situated on lateral end of the eye
path of tears
tears drain across the eye into the lacrimal canaliculi, then the lacrimal sac, and into the nasolacrimal duct, which empties into the nasal cavity
dilute salt solution
lysozyme (enzyme that destroys bacteria)
function of tears
lubricate the eye
extrinsic eye muscles
6 muscles attach to the outer surface of the eye
produce gross eye muscles
moves eye laterally
cranial nerve VI -- abducens
moves eye medially
cranial nerve III -- oculomotor
elevates eye and turns it medially
depresses eye and turns it medially
elevates eye and turns it laterally
depresses eye and turns it laterally
cranial nerve IV -- trochlear
internal structures of the eyeball
humors and fluids
how many layers form the wall of the eyeball?
what are they three layers of the eyeball?
fill the interior of the eyeball
lens divides the eye. . .
into 2 chambers
fibrous layer of the eyeball
sclera and cornea
white connective tissue layer
seen anteriorly as the white of the eye
holds structure of the eye
1st area where light enters the eye
transparent, central anterior portion
allows for light to pass through
repairs itself easily
the only human tissues that can be transplanted without fear or rejection due to lack of blood vessels
a blood rich nutritive layer that contains pigment (prevents light from scattering)
how is the choroid modified anteriorly?
into two smooth muscle structures
ciliary body and iris
attached to lens by a suspensory ligament called the ciliary zonule
regulates the amount of light entering the eye
the pigmented layer that gives the eye color
rounded opening in the iris
while within iris, black part is the back of the retina
retina and rods and cones
how many layers does the retina contain?
what are the two layers of the retina?
outer pigmented layer absorbs light and prevents it from scattering
inner neural layer contains receptor cells (photoreceptors)
what are the photoreceptors?
rods and cones
electrical signals pass from photoreceptors via __________
two neuron chain
what are the two neurons in a two neuron chain?
bipolar cells and ganglion cells
how do signals leave the retina to go to the brain?
via the optic nerve
the blind spot
where the optic nerve leave the eyeball
cannot see images focused on the optic disc because it lacks rods and cones
most are found toward the edges of the retina
allow vision in dim light and peripheral vision
all perception is in gray tones
allow for detailed color vision
densest in the center of the retina
lateral to the blind spot
area of the retina with only cones
visual acuity is here
3 types of cones (RBG)
each cone type is sensitive to different wavelengths of visible light
what segments does the lens divide the eye into?
anterior to the lens
contains aqueous humor
posterior to the lens
contains vitreous humor
watery fluid found between the lens and cornea
similar to blood plasma
helps maintain intraocular pressure
provides nutrients for the lens and cornea
reabsorbed into venous blood through the sclera venous canal/canal of schlemm
prevents eye from collapsing
instrument used to illuminate the interior of the eyeball and fundus (posterior wall)
can detect diabetes, arteriosclerosis, degeneration of the optic nerve and retina
light must be focused to a point on the ___ for optimal vision
light is _______ by the cornea, aqueous humor, lens, and vitreous humor
the eye is set for _______
distant vision (over 20 ft away)
the lens must change shape to focus on closer objects (less than 20 ft away)
image formed on the retina is a ________
real images are . . .
reversed L from R
smaller than the object
bundles of axons that exit the back of the eye carrying impulses from the retina
location where the optic nerves cross
fibers from the medial side of each eye cross over to the opposite side of the brain
contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye
synapse with neurons in the thalamus
axons from the thalamus run to the occipital lobe
synapse with cortical cells and vision interpretation (seeing) occurs
pathway of impulses from the retina to the point of visual interpretation
visual cortex in occipital lobe of the brain
overlap for each eye
each eye sees a slightly different view
results and provides depth perception
eye focuses images correctly on the retina (normal vision)
distant objects appear blurry
light from those objects fails to reach the retina and are focused in front of it
results from having an eyeball that is too long
near objects appear blurry, whereas distant objects are clear
distant objects are focused behind the retina
results from an eyeball that is too short or from a lazy lens
images are blurry
results from light focusing as lines, not points, on the retina because of unequal curvatures of the cornea or lens
reflexive movement of the eyes medially when we focus on a close object (going cross eyed when a pen is brought to your nose)
bright light causes pupils to constrict
accommodation pupillary reflex
viewing objects causes PUPILS to constrict
how many senses does the ear house?
what are the two senses that the ear houses?
hearing and equilibrium (balance)
what are the receptors in the ear?
how many areas is the ear divided into?
what are the divisions of the ear?
external (outer) ear
internal (inner) ear
external acoustic meatus (auditory canal)
only involved in collecting sound waves
narrow chamber in the temporal bone
lined with skin and ceruminous (earwax) glands
glands secrete cerumen (earwax)
cerumen traps foreign objects and repels insects
ends at the tympanic membrane (eardrum)
middle ear cavity (tympanic cavity)
air-filled mucosa-lined cavity within the temporal bone
involved in sense of hearing
located btwn tympanic membrane and by a bony wall with two openings
3 bones (ossicles)