CH 16 - Special Senses Part 2`

lens and ciliary zone divides the eye into

two segments

• anterior and posterior

posterior segment - vitreous humor

filled with vitreous humor

• clear, jelly-like substances

• composed of collagen fibers and water-rich ground substance

• more than 98% water

functions of vitreous human

• transmit light through eye

• supports posterior surface of the lens

• hold the neuron retina against the pigmented retina

• helps maintain intraocular pressure

• counteracts pulling forces from extrinsic eye muscles

internal chambers and fluids - anterior segment - aqueous humor

divided into

• anterior chamber (between cornea and iris)

• posterior chamber (between iris and lens)

aqueous humor

clear fluid similar to blood plasma

• continuously produced and replaced

functions of aqueous humor

• maintains constant intraocular pressure

• provides internal support for the eyeball

• delivers oxygen and nutrients to the avascular cornea

aqueous human is renewed continuously

1. aqueous human is formed by filteration from the capillaries in the ciliary processes

2. flows from the posterior chamber through the pupil into the anterior chamber; some also flows through the vitreous humor

3. aqueous human is reabsorbed into the venous blood by the scleral venous sinus luag

glaucoma occurs when

aqueous humor drains more slowly than it is produced

• causes a buildup within the eye

• leads to increased intraocular pressure

glaucoma cause

• usually results from obstruction of aqueous humor outflow

• often due to clogging of the drainage pathway into the scleral venous sinus

effects of increased intraocular pressure

• compresses the retina

• damages the optic nerve

• can eventually lead to blindness

the lens

a thick, transparent, biconvex disc

• held in place by its ciliary zonule

lens epithelium -

covers the anterior surface of the lens

lens fibers form the

bulk of the lens

• new lens fibers are continuously added

• lens enlarges throughout life

a cataracts is

the clouding go the lens

• causes vision too appear blurry or distorted, as if looking though frosted glass

cataracts - types

can be either congenital (present at birth) but most commonly develop as a result of aging

cataracts - risk factors

• excessive exposure to sunlight

• heavy smoking

• certain medications,

  • oral steroids, long-term aspirin use, tamoxifen

cataracts - underlying cause

thought to result from inadequate nutrient delivery to deeper lens fibers

cataracts - effects on vision

• reduced transparency of the lens

• blurred, cloudy, or distorted vision

• difficulty seeing clearly

cataracts - treatment

surgical removal of the clouded lens, replacement with an artificial intraocular lens

light rays converge on the

retina at a single focal point

lens is convex -

projects images that upside down and revered from left to right onto the retina

images are “flipped back” by the

cerebral cortex

light blinding structures called refractory media are the

lens, cornea, and humors

accommodation -

curvature of the lens is adjustable

• allows for focusing on nearby objects

accommodation controlled by

parasympathetic fibers that signal ciliary muscle to contract

focusing is accompanied by

pupillary constriction

• prevents divergent rays from entering the eye and passing through the edges of the lens

myopic eye

nearsighted

• eye ball too long

  • uncorrected - focal point is in front of retina

hyperopic eye

farsighted

• eyeball too short; focal point is behind the retina

  • uncorrected - focal point is behind retina

refractive errors are common vision problems that affect

hoe the eye focuses light t

he four main types of refractive errors

myopia, hyperopia, astigmatism, and presbyopia

myopia (nearsightedness) occurs when the

eyeball is too long to the cornea is too curved, causing light to focus in front of the retina instead of directly on it

• results in clear close objects, but blurry far objects

hyperopia (farsightedness) eyeball is too

short or the cornea is not curved enough → causes light to focus behind the retina

• clear vision for distant object, blurry vision for close objects

astigmatism occurs when

the cornea or lens has an irregular shape, causing light to focus enevenly on the retina

astigmatism results in

• Blurred or distorted vision at all distances

• Difficulty seeing vertical lines more clearly than horizontal ones (or vice versa)

• resbyoia pPotential issues with night driving

presbyopia is an

age-related condition (40-45); occurs due to the hardening of the eye’s natural lens

presbyopia leading to

● Difficulty focusing on close objects

● The need to hold reading materials at arm's length

● Eyestrain or headaches when doing close-up work

most visual information travels to the

cerebral cortex (responsible for conscious “seeing”)

pathway begins in the

retina

visual pathway

light activates photoreceptors → signal bipolar cells → signal ganglion cells → axons of ganglion cells exit the eye as the optic nerve

at the optic chiasma, axons from the medial halves of the

retinas intersect

• provides each visual cortex with information on the opposite half of the visual field as seen by both eyes

the visual cortex compares two similar but different images and creates

the “perception of depth”

retinopathy of prematurity

• blood vessels grow within the eyes of premature infants

• vessels have weak walls - causes hemorrhaging and blindness

trachoma

contagious infection of the conjunctiva

the ear -

receptor organ for hearing and equilibrium

the ear is composed of three main regions

outer, middle, and internal eat

outer and middle ear -

functions in hearing

internal ear - functions in both

hearing and equilibrium

eat is a receptor for

sound impulses as well as an energy transducer

• covert sound energy into electrical energy of an action potential

the outer (external) ear - composed on

auricle (pinna), external acoustic meatus, tympanic membrane

auricle (pinna)

helps direct sounds

external acoustic meatus contains

hairs, sebaceous glands, and ceruminous glands

tympanic membrane forms the

boundary between the external and middle ear

middle ear =

air-filled sac

tympanic cavity -

transmits vibrations from the eardrum across cavity to the fluid of the inner ear

tiny ligaments suspend the

ossicles in the middle ear and tiny synovial joints link the ossicles into a chain

by concentrating the vibrations of the eardrum onto the mulch small oval window, the ossicles

amplify the pressure of the sound vibration about 20-fold

without the ossicles, people could hear only

loud sounds

pharyngotympanic tube -

links the middle ear to the pharynx

pharyngotympanic tube is normally

flattened; opens when you yawn or swallow so air can equalize with outside pressure

auditory ossicles =

malleus (hammer), incus (anvil), stapes (stirrup)

oval window and round window -

both opening are between the middle ear and inner ear

sound vibrations enter the inner ear primarily through the

oval window

oval window receives sound waves directly from the

middle ear

round window acts a

pressure release valve

round window - maintains

fluid pressure within the cochlea by moving in the opposite direction of the oval window

oval window is situated directly between the

middle ear a dn vestibule of the inner ear

round window is positioned slightly

below and behind the oval window

auditory tube

duct that connects the middle ear to the nasopharynx

auditory tube - equalizing pressure

helps to balance the pressure in the middle ear, which can be felt as your ears are popping

auditory tube - draining fluid

helps to draw fluid from the middle ear

auditory tube - protecting the eat

helps to protect the ear form hearing sounds caused by the body and nasal drainage

auditory tube - optimizing sound transmission

helps to optimize the transmission of sound in the middle ear

Eustachian tube

• is made of cartilage and bone

  • normally closed, but opens when the pharynx or mandible moves, like when swallowing or chewing t

two skeletal muscles occur in middle ear cavity

tensor tympani snd stapedius

• contract reflexively to limit the vibration of the ossicles, preventing damage to the hearing receptors

tensor tympani -

originates on the cartilage part of the pharyngotympanic tube and inserts on the malleus

stapedius -

runs from the posterior wall of the middle ear to the stapes

inner ear components

semicircular canal, cochlea, vestibule

semicircular canals

fluid filled tubes that communicate information about the bodies position to the cerebellum via the vestibulocohclear nerve

cochlea -

snail shaped structure that contain hair cells (mechanoreceptors) that transmit auditory input to the temporal lobe

vestibule -

space between semicircular canals and vestibule

cochlear duct (scala media)

located within the cochlea

• contains the sensory receptors for hearing

modiolus -

pillar of bone that cochlea wraps around

within cochlea are three regions

• one with endolymph (internal water)

• two are perilymph (surrounding water)

spiral organ -

receptor organ for hearing within the cochlea (hair cells)

spiral organs contains

inner and outer rows of hair cells (receptors)

spiral organ - tips of these hairs are called

stereo cilia which are embedded within tectorial membrane

• at their base, hair cells synapse with the cochlear nerve

role of cochlea in hearing - sound waves travel through the

auditory canal, striking the eardrum (vibrate)

role of cochlea in hearing - vibration is passed though

the malleus, the incus, and the stapes

role of cochlea in hearing - stapes the vibrates the

oval window of the vestibule canal, translating motion into the perilymph fluid fo the cochlea

role of cochlea in hearing - the vibrating fluid begins stimulating the

endolymph fluid in the membranous area of the cochlea

role of cochlea in hearing - the endolymph fluid in turn stimulates the

hair cells, transmit the impulses to the brain over the auditory (cochlear) nerve

inner ear is responsible for

encoding information about equilibrium

sense of balance occurs in the

vestibular apparatus (vestibule and semicircular canal)

sense of balance involves

multiple receptors, as information is integrated form numerous structures

types of equilibrium

static (gravitational) and dynamic (rotational)

static (gravitational) equilibrium -

involves the movement of the head with gravity

vestibule - houses receptors for

static equilbirum and linear acceleration

dynamic (rotational) equilibrium -

involved acceleration of the head in rotation, horizontal, and vertical movements

semicircular canals- houses receipts for

rotational equilibrium

• hair cells with stereo cilia detect movement of fluid within the inner ear (changes in position and acceleration)

macula -

sense organ containing stereo cilia

• oriented 90* to one another; respond to positions in different planes