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Objective:
 Describe and observe how taste and smell are
related to one another
 Describe different sensory receptors found in the
body

Journal: What are your five senses?

Ability to sense changes in the environment is
necessary for maintaining homeostasis

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All sense organs must be able to detect a
stimulus in the environment
Depending on the stimulus, a different
receptor will be activated
Signal is transmitted over a nervous system
“pathway” to brain
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Photoreceptors – stimulated by light, in eye
Chemoreceptors – stimulated by chemicals, in
tongue and nose
Pain receptors – stimulated by physical damage
Thermoreceptors – stimulated by change in
temperature
Mechanoreceptors – stimulated by change in
position
Taste and smell:
 Receptors are chemoreceptors

Associated with food intake, influence flow of
digestive juices, and affect appetite


Chemoreceptors in taste buds in mouth and
throat
Taste bud consists of
 Taste pore
▪ Opening through which fluids in mouth come into
contact with surface of receptor cells
 Taste receptor cells
▪ Modified epithelial cells with surface folds called
microvilli that contain chemical receptors


Located on papillae
(bumps on your
tongue and throat)
Two Types:
 Fungiform papillae
▪ Small, all over the top
and sides of the tongue
 Circumvallate Papillae
▪ Large, on the back of the
tongue

Taste buds consist of:
 ~50 receptor cells
surrounded by
supporting cells
 Basal cells develop into
supporting cells then
receptor cells
▪ Gustatory hairs
project through the
taste pore

Four kinds of tastes caused by different
chemical stimuli: Sweet, Sour, Bitter, and Salty


Chemoreceptors
that allow for
smell are called
olfactory
receptors
Located in the
nasal cavity

Olfactory neurons
 Located in the olfactory epithelium and sense
changes in smell through the olfactory hairs
 Connect to olfactory nerve tract

Supporting Cells
 Metabolic and physical support cells for the
olfactory neurons
The physical stimuli are chemical substances
carried in the air that are dissolved in the mucus in
the nose.
 Pathway:
 Olfactory Hairs  Olfactory Neurons  Olfactory
Nerve in the Brain
 Neurons connect directly into the brain from the
nasal epithelium through the cribriform plate


Journal: Explain why ice cream tastes
different than a lemon.

Two functions:
 Hearing and Equilibrium

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Physical forces from sound and movements
stimulate the mechanoreceptors
Three parts of the ear:
 External ear, Middle ear, Inner ear

Made up of:
 Auricle (aka Pinna) – appendage on side of head
 External auditory canal – curving tube, about 1 in long
▪ Ends at ear drum (aka Tympanic membrane)
▪ Separates external and middle ear
▪ Auditory canal lined with hair and contains
ceruminous glands
▪ Produces cerumen (ear wax) to protect inner ear
▪ Sound waves travel thru canal, strike the tympanic
membrane and cause it to vibrate
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Tiny cavity hollowed out of temporal bone
Also connects to the throat by
Pharyngotympanic tube
 Sore throat could spread to ear, causes middle ear
infection

Contains three small bones called ossicles
 Names describe shape:
▪ Malleus (hammer), Incus (anvil), Stapes (stirrup)
Malleus attached to tympanic
membrane and incus
 Incus attached to stapes
 Stapes presses against a
membrane that covers the oval
window (small opening in inner
ear)
 Sounds cause tympanic
membrane to vibrate, which is
then transmitted and amplified by
ossicles

 Causes movement of fluid in inner ear

Mechanoreceptors found in fluid-filled chambers
known as the membranous labyrinth
 Endolymph – thick fluid

Bony labyrinth covers membrane labyrinth to
provide protection
 Perilymph – watery fluid between bony and
membranous labyrinth
Bony labyrinth divided into three parts:
 Cochlea (hearing)– snail-like shape, contains
organ of Corti which is covered in hairs
 Surrounded by endolymph, sound waves causes liquid
to move, which moves hairs
▪ Nerve impulse stimulated when hairs are bent

Semicircular Canal (balance) – 3 half-circle canals
 Endolymph surrounds receptors (crista ampullaris)
which are covered in hair
▪ Nerve impulse stimulated by rotation of head

Vestibule (sense gravity) – btw cochlea and s.
canal
In US – over 6 million people with a hearing deficit
CONDUCTIVE DEAFNESS
 Conditions in outer or middle ear blocks vibrations

 External auditory canal blocked with wax, water
 Scarring of eardrum
NERVE DEAFNESS
 Problem in cochlea or auditory pathway to brain
 Receptors in organ of Corti can’t interpret sounds
 Correction - chochlear implant

Nerve impulse doesn’t make it to brain

http://www.youtube.com/watch?v=Go9pONJ
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Frequency
8 kHz
10 kHz
12 kHz
14 kHz
15 kHz
16 kHz
17 kHz
18 kHz
19 kHz
20 kHz
21 kHz
22 kHz
Heard?
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Could you hear all the frequencies?
What is your hearing threshold?
How do dog whistles work?
Does the frequency of sound you can hear
change as you age?

Objective:
 Label and describe the structures of the eye
 Explain how the eye allows you to see

Journal:
 List and explain the difference between the two
types of deafness.

The eye is covered with three layers of tissue:
sclera, choroid, retina

SCLERA (aka “whites of the eyes”)
 Made up of tough, fibrous tissue
 Front has a transparent portion – Cornea
▪ Covers iris – colored portion of eyes
 Conjuntiva – mucous membrane keeps eye moist
 Lacrimal Gland – produces tears
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CHOROID
 Middle layer of eyeball
 Contains dark pigment to prevent scattering of
incoming rays of light
 Made up of 2 involuntary muscles: Iris and ciliary
▪ Pupil is actually a hole in the center of the iris muscle
▪ 2 kinds of muscles in iris: circular – constricts pupil,
lateral – dilates pupil
▪ Ciliary muscle helps to focus on objects
▪ Relaxed for distance, contracted for close

RETINA
 Contains microscopic
photorecepotors:
▪ Rods – nightime vision, black
and white
▪ Cones – daytime vision, color
▪ 3 types detect color – red,
green, blue

Macula Lutea – yellowish area near center of
retina
 Surrounds fovea centralis – a depression that
contains the most cones

Visual sharpness is obtained by focusing the
image on the fovea centralis
Fluid maintains intraocular pressure of eyeball
 Fluid refracts light rays to focus on retina
 Aqueous Humor – fluid in front of lens
 Vitreous Humor – Jellylike material in the posterior
cavity
 Lens – directly behind pupil
 Held in place by ligament
 Elastic to allow change of shape
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Light stimulates photoreceptors
Light enters the eye at the pupil, and is
refracted by lens to focused on retina
Nerve impulses created by rods and cones
are collected and exit with the optic nerve
 No rods cones are present where optic nerve
exists which is known as the blind spot

Myopia - Image focuses in front of retina,
distant objects blurry

Hyperopia - Image focuses behind retina, close
objects blurry
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Astigmatism – Abnormal curvature of cornea
or lens, fails to refract light properly
CATARACTS
 Lens of eye becomes cloudy so less light enters the eye
 If completely opaque, person will be blind
 CORRECTION – surgery to replace lens
GLAUCOMA
 Aqueous humor not drained properly, intraocular pressure
builds up
 Distorts soft tissue of the eye and can cause blindness
 CORRECTION - surgery to drain fluid, drugs to increase
drainage
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Unable to distinguish certain colors
Caused by a recessive gene on the X
chromosome
 Men more likely to be colorblind

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Occurs when cones are nonfunctional
Most common – red cones missing
 Can’t distinguish red from green

https://www.youtube.com/watch?v=ea_xOq
NvntA