Accessory Structures of the Accessory Structures of the EyeEye

Eyebrow:Eyebrow: shade the eye, shade the eye, protect from sweatprotect from sweat

Eyelids:Eyelids: protects, protects, prevents drying of the prevents drying of the eye.eye.

Conjunctiva:Conjunctiva: membrane membrane that lines the eyelid and that lines the eyelid and covers the white of the covers the white of the eye. Prevents the eye eye. Prevents the eye from drying. from drying. Pink eye is an

infection of the conjunctiva

Structure of the EyeStructure of the Eye

Structure of the EyeStructure of the Eye

CorneaCornea:: transparent layer, transparent layer, helps focus light rays helps focus light rays

ScleraSclera:: white part of the eye, white part of the eye, protects and shapes the eyeprotects and shapes the eye

Choroid:Choroid: black-brown inner black-brown inner layer, absorbs excess light layer, absorbs excess light

LensLens:: transparent, flexible transparent, flexible structure, focuses images structure, focuses images

Ciliary body:Ciliary body: ring of smooth ring of smooth muscle, controls the shape of the lens.muscle, controls the shape of the lens.

The cornea is the only tissue that can be transplanted with almost no possibility of rejection.

Cataract = clouding of lens caused by age, smoking, sun damage. Vitamin C decreases risk.

Structure of the Eye (cont.)Structure of the Eye (cont.) IrisIris:: colored part of the eye, has muscles colored part of the eye, has muscles

that change size of the pupilthat change size of the pupil PupilPupil:: opening in center of opening in center of

iris, allows light to enter the eye iris, allows light to enter the eye RetinaRetina: contains photoreceptors: contains photoreceptors

– Rods:Rods: fuzzy vision in low light (gray fuzzy vision in low light (gray scale)scale)

– Cones:Cones: sharp, color sharp, color vision (red, blue, green)vision (red, blue, green)

Optic discOptic disc::“blind spot”, lacks “blind spot”, lacks photoreceptorsphotoreceptors

Color blindness is due to a lack of one or more cones. Red-green is most common.

Humans have about 100 million rods and 3 million cones.

Structure of the Eye (cont.)Structure of the Eye (cont.)

FoveaFovea: depression in retina, : depression in retina, produces the sharpest vision produces the sharpest vision

Vitreous humorVitreous humor:: clear gel that clear gel that transmits light and supports the lens transmits light and supports the lens and retina.and retina.

Aqueous humorAqueous humor:: fluid that fluid that nourishes the lens, cornea, and nourishes the lens, cornea, and retina.retina. Glaucoma=aqueous humor

blocked, pressure builds on optic nerve and retina. May cause blindness.

The fovea is about the size of the head of a pin

Basics of SightBasics of Sight We see reflected light.We see reflected light. Light passes through the Light passes through the

cornea and lens, is focused cornea and lens, is focused on the photoreceptors of the on the photoreceptors of the retina.retina.

Image on retina is upside Image on retina is upside down and reversed from left down and reversed from left to right. The visual cortex of to right. The visual cortex of the cerebrum corrects this the cerebrum corrects this so objects are seen in the so objects are seen in the correct position.correct position.

Newborns have very poor eyesight and cannot see colors.

Diabetes and arteriosclerosis can both cause blindness.

How we see color http://www.youtube.com/watch?v=nAbxfKPKorc

Smell and TasteSmell and Taste Senses of smell and taste are very Senses of smell and taste are very

closely linked. closely linked. – Both are chemoreceptors (respond to Both are chemoreceptors (respond to

changes in chemical concentrations).changes in chemical concentrations).– 80% of flavor actually comes from smell.80% of flavor actually comes from smell.

Primary taste sensations include sweet, Primary taste sensations include sweet, salty, sour, bitter, and umami.salty, sour, bitter, and umami.– Carbs stimulate sweet, acids stimulate sourCarbs stimulate sweet, acids stimulate sour– Metal ions stimulate salty flavorMetal ions stimulate salty flavor– Alkaloids stimulate bitter tasteAlkaloids stimulate bitter taste– Umami is stimulated by specific amino acids.Umami is stimulated by specific amino acids.

http://www.pbs.org/wgbh/nova/body/neuroscience-taste.html (13min)

Purpose of TastePurpose of Taste

Umami = intake of proteinUmami = intake of protein Sweet = intake of carbohydratesSweet = intake of carbohydrates Salty = intake of some mineralsSalty = intake of some minerals Sour = Vitamin CSour = Vitamin C Bitter = protective, many poisonous Bitter = protective, many poisonous

and spoiled substances are bitter.and spoiled substances are bitter.

Did you know…Did you know… Humans have about 12 million olfactory Humans have about 12 million olfactory

receptors, 500 receptor types, and can receptors, 500 receptor types, and can discern 10,000 scents.discern 10,000 scents.

Umami is involved in sensing the taste Umami is involved in sensing the taste of steak, some cheeses, and MSG.of steak, some cheeses, and MSG.

Humans have about 10,000 taste buds.Humans have about 10,000 taste buds. Don’t believe those taste bud maps, all Don’t believe those taste bud maps, all

tastes can be elicited from all areas that tastes can be elicited from all areas that contain taste buds.contain taste buds.

Spicy foods actually stimulate pain Spicy foods actually stimulate pain receptors.receptors.

The Ear

Structures of the EarStructures of the Ear External ear:External ear:

– Auricle (pinna): collects sound wavesAuricle (pinna): collects sound waves– External auditory meatusExternal auditory meatus

Middle ear:Middle ear:– Tympanic membrane (eardrum)Tympanic membrane (eardrum)– Malleus, incus, stapesMalleus, incus, stapes

Inner ear:Inner ear:– CochleaCochlea– Semicircular canalsSemicircular canals

Auditory (eustachian) tube:Auditory (eustachian) tube: connects middle connects middle ear to throat. Helps maintain air pressure on ear to throat. Helps maintain air pressure on each side of the tympanic membrane.each side of the tympanic membrane.

Jaw movements (talking, chewing) help push old, dry earwax out of the ear.

The auditory tube is usually closed. It opens when we yawn or swallow to equalized pressure in the middle ear.

How we HearHow we Hear Sound waves (vibrations) enter the ear.Sound waves (vibrations) enter the ear. Vibrations hit the tympanic membrane Vibrations hit the tympanic membrane

which passes the vibration to the which passes the vibration to the malleus, incus, and stapes. malleus, incus, and stapes.

Vibration of the stapes at the oval Vibration of the stapes at the oval window causes the fluid in the cochlea window causes the fluid in the cochlea to move.to move.

Movement of the fluid stimulates Movement of the fluid stimulates receptors (cochlear hair cells).receptors (cochlear hair cells).

Hair cells are sensitive to specific Hair cells are sensitive to specific frequencies.frequencies.

Ear canal

Ear drum(tympanicmembrane) Eustachian tube

Cochlea

Auditory nerve

Semicircular canal

Oval window

Malleus

Incus

Stapes

Roundwindow

Sound

DecibelsDecibels Measure sound intensity.Measure sound intensity. 50 dB = normal conversation50 dB = normal conversation 70 dB = noisy restaurant70 dB = noisy restaurant 90 db = lawnmower, frequent 90 db = lawnmower, frequent

or prolonged exposure causes or prolonged exposure causes hearing loss.hearing loss.

120 dB = rock concert, causes 120 dB = rock concert, causes discomfortdiscomfort

140 dB = gunshot, causes pain 140 dB = gunshot, causes pain and immediate damageand immediate damage

EquilibriumEquilibrium Senses the position of body parts, helps Senses the position of body parts, helps

maintain stability and posture, detects maintain stability and posture, detects motion, and helps maintain balance.motion, and helps maintain balance.

When the head moves or rotates, fluid in the When the head moves or rotates, fluid in the semicircular canals moves causing hair cells semicircular canals moves causing hair cells to bend (stimulates the nerves). to bend (stimulates the nerves).

Also influenced by vision and stretch Also influenced by vision and stretch receptors in muscles and tendons. receptors in muscles and tendons.

Nystagmus is a type of eye movement that occurs during and after rotation.

Motion sickness http://www.youtube.com/watch?v=evBdytnlXnM