Download Senses Notes

Accessory Structures of the Eye

Eyebrow: shade the eye,
protect from sweat
 Eyelids: protects, prevents
drying of the eye.
 Conjunctiva: membrane
that lines the eyelid and
covers the white of the eye.
Prevents the eye from drying.
Pink eye is an infection
of the conjunctiva
Structure of the Eye
Structure of the Eye

Cornea: transparent layer,
The cornea is the only
tissue that can be
transplanted with almost
no possibility of rejection.
helps focus light rays
 Sclera: white part of the eye,
protects and shapes the eye
 Choroid: black-brown inner
Cataract = clouding of
layer, absorbs excess light
lens caused by age,
smoking, sun damage.
 Lens: transparent, flexible Vitamin C decreases
risk.
structure, focuses images
 Ciliary body: ring of smooth
muscle, controls the shape of the lens.
Structure of the Eye (cont.)

Iris: colored part of the eye, has muscles
that change size of the pupil
Color blindness is
due to a lack of
 Pupil: opening in center of
one or more
Rediris, allows light to enter the eye cones.
green is most
 Retina: contains photoreceptors common.
– Rods: fuzzy vision in low light (gray scale)
Humans have about
– Cones: sharp, color
100 million rods and 3
vision (red, blue, green) million cones.
 Optic disc:“blind spot”, lacks photoreceptors
Structure of the Eye (cont.)
 Fovea:
The fovea is about
the size of the
head of a pin
depression in retina,
produces the sharpest vision
 Vitreous humor: clear gel that transmits
light and supports the lens and retina.
 Aqueous humor: fluid that nourishes the
lens, cornea, and retina.
Glaucoma=aqueous humor blocked,
pressure builds on optic nerve and
retina. May cause blindness.
Basics of Sight
We see reflected light.
 Light passes through the cornea
and lens, is focused on the
photoreceptors of the retina.
 Image on retina is upside down
and reversed from left to right.
The visual cortex of the
cerebrum corrects this so objects
are seen in the correct position.

Newborns have very poor
eyesight and cannot see colors.
How we see color
http://www.youtube.com/watch?v=nAbxfKPKorc
Diabetes and
arteriosclerosis can
both cause
blindness.
Smell and Taste

Senses of smell and taste are very closely
linked. http://www.pbs.org/wgbh/nova/body/neuroscience-taste.html (13min)
– Both are chemoreceptors (respond to changes in
chemical concentrations).
– 80% of flavor actually comes from smell.

Primary taste sensations include sweet, salty,
sour, bitter, and umami.
– Carbs stimulate sweet, acids stimulate sour
– Metal ions stimulate salty flavor
– Alkaloids stimulate bitter taste
– Umami is stimulated by specific amino acids.
Purpose of Taste
Umami = intake of protein
 Sweet = intake of carbohydrates
 Salty = intake of some minerals
 Sour = Vitamin C
 Bitter = protective, many poisonous and
spoiled substances are bitter.

Did you know…
Humans have about 12 million olfactory
receptors, 500 receptor types, and can
discern 10,000 scents.
 Umami is involved in sensing the taste of
steak, some cheeses, and MSG.
 Humans have about 10,000 taste buds.
 Don’t believe those taste bud maps, all tastes
can be elicited from all areas that contain
taste buds.
 Spicy foods actually stimulate pain receptors.

The Ear
Structures of the Ear
External ear:
– Auricle (pinna): collects sound waves
Jaw movements
– External auditory meatus
(talking, chewing)
help push old, dry
 Middle ear:
earwax out of the
ear.
– Tympanic membrane (eardrum)
The auditory tube is
– Malleus, incus, stapes
usually closed. It opens
 Inner ear:
when we yawn or swallow
to equalized pressure in
– Cochlea
the middle ear.
– Semicircular canals
 Auditory (eustachian) tube: connects middle ear to
throat. Helps maintain air pressure on each side of
the tympanic membrane.

How we Hear
Sound waves (vibrations) enter the ear.
 Vibrations hit the tympanic membrane which
passes the vibration to the malleus, incus,
and stapes.
 Vibration of the stapes at the oval window
causes the fluid in the cochlea to move.
 Movement of the fluid stimulates receptors
(cochlear hair cells).
 Hair cells are sensitive to specific frequencies.

Semicircular canal
Stapes
Oval window
Auditory nerve
Incus
Malleus
Round
window
Cochlea
Ear drum
(tympanic
membrane)
Sound
Ear canal
Eustachian tube
Decibels
Measure sound intensity.
 50 dB = normal conversation
 70 dB = noisy restaurant
 90 db = lawnmower, frequent or
prolonged exposure causes hearing
loss.
 120 dB = rock concert, causes
discomfort
 140 dB = gunshot, causes pain and
immediate damage

Equilibrium
Senses the position of body parts, helps maintain
stability and posture, detects motion, and helps
maintain balance.
 When the head moves or rotates, fluid in the
semicircular canals moves causing hair cells to bend
(stimulates the nerves).
 Also influenced by vision and stretch receptors in
muscles and tendons.

Motion sickness
http://www.youtube.com/watch?v=evBdytnl
XnM
Nystagmus is a type of eye
movement that occurs
during and after rotation.