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F. Sensory Receptors
What are sensory receptors?
http://www.youtube.com/watch?v=1vLsZ_dXFAg&feature=related
a life without pain
Sensory Receptors are:
• highly modified ends of sensory
neurons that are activated by a specific
stimulus
• specialized cells that receive stimuli and
translate them to a nerve message in a
sensory neuron

Sensory adaptation occurs once the receptor
has become accustomed to the stimulus. The
neuron ceases to fire even though the stimulus
is still present (often occurs with the sense of
smell).
1. Taste and Smell
Taste
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there are 300 taste buds on the tongue
the taste is perceived in the parietal lobe of the brain
the tongue has four different taste receptors (salty,
sweet, sour and bitter) See fig. 12.25
http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/taste.html
http://www.agen.ufl.edu/~chyn/age2062/lect/lect_24/lecture_24.htm
Smell
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olfactory (smell) cells are located in the
nasal cavity
airborne chemicals combine with the
receptor ends on olfactory cells to
create an action potential
the smell is perceived by the
temporal lobe of the brain
the senses of taste and smell work
together
http://instruct1.cit.cornell.edu/courses/biog105/pages/demos/105/unit10/tastesmell.html
2. Pressure

a mechanical stimulus involving the movement
of the skin or changes in the body surface
 Includes touch and pain
3. Proprioreceptors
a
mechanical stimulus involving
movement of the muscles, tendons and
joints in the arms and/or legs
 Responsible for maintaining body position
4. Heat and cold
 thermoreceptors
detect a change in
temperature on the surface of the skin
5. Balance
 body
movement equilibrium is maintained
by specialized structures in the inner ear
 Fluid movement causes the movement of
special hair cells in the inner ear, which
results in a stimulus and eventual
response
6. Eye (Photoreceptors)
Why do we see illusions? Mark Changizi
 http://www.youtube.com/watch?v=1xcvWS
eZPbw&list=PLJicmE8fK0Ehrg3meytY7D
T8LJiwuU3Th&index=36
 PPT
Illusions
 ..\Optical_Illusions.ppt
a. Structures
http://www.youtube.com/watch?v=Sqr6LKIR2b8
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sclera (outer eye) – the white portion of the eye,
supports and protects photocells
cornea (outer eye) – transparent tissue that bends
light toward the pupil. Requires oxygen and
nutrients but has no blood vessels so most of the
oxygen absorbed from the atmosphere are found in
tears
lens (accessory) – focuses the image on the retina,
flatten/narrows as you focus near or far
iris (middle eye) – regulates the amount of light
entering the eye
a. Structures
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pupil (middle eye) – hole in the iris, allows light to
penetrate the eye
aqueous humor (accessory) – supplies the cornea
with nutrients and bends light entering the eye
vitreous humor (accessory) – holds retina and lens
in place
retina (inner eye) – contains photoreceptors that
respond to light
fovea centralis (inner eye) –sensitive area of the
retina, contains only cones
a. Structures
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blind spot (inner eye) – area where the optic nerve
attaches to the retina
choroid layer (middle eye) – contains pigments that
prevent the scattering of light in the eye by
absorbing stray light – contains blood vessels
optic nerve (accessory) – carries impulses from the
rods and cones to CNS
rods – used for seeing in dim light
cones – identify color, used for sharp vision
http://www.accesslearning.com/videodetail.cfm?ass
et_guid=599B05FF-4640-4B57-8C419CF68CE5479F
(25 min)
b. Focusing image
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light passes through the cornea, lens and fluid
humours where it is bent
the image is sent to the fovea centralis of the retina
where it if fixed smaller, upside down and reversed
from left to right
when nearby objects are viewed, the ciliary muscles
contract causing the lens to become rounder
when far-away objects are viewed, the ciliary
muscles relax causing the lens to become flattened
the ability of the lens to change shape in order to
focus images clearly on the retina is a reflex called
accommodation (6 m away requires no
accommodation)
c. Chemistry of vision
 vision
begins as light is focused on the
light-receiving cells called photoreceptors
(rods and cones)
Rods
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rods are responsible for detecting motion and
peripheral vision
rods are spread throughout the retina but are more
concentrated on the outside edges
rods contain a pigment called rhodopsin, made of
Vitamin A (retinal) and a protein called opsin
http://health.howstuffworks.com/eye2.htm
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when a small unit of light strikes the rhodopsin
molecule it splits into retinal (pigment) and opsin
(protein).
A cascade of reactions result in the closure of ion
channels in the rod cell’s plasma membrane
Inhibition of an inhibitory transmitter causes an action
potential to travel to the visual areas of the cerebral
cortex
A signal is transmitted to the optic nerve
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in bright light, rhodopsin is broken down faster than it
can be restored
• rods incapacitated until they can be restored
in the absence of light, retinal is changed to Vitamin
A, and with the addition of ATP, the Vitamin A
recombines with opsin to restore rhodopsin levels
nocturnal animals have a higher ratio of rods to cones
Rods allow for vision at night
Cones

cones allow for colour vision
 vitamin A combines with three different protein
opsins in the cones, each sensitive to the three
primary colors of light (red, blue, green)
 each pigment is located in a different cone
http://health.howstuffworks.com/eye2.htm
d. Visual Interpretation
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image is sent to the brain via stimulation of photoreceptor cells
(rods and cones) which generate an action potential via the optic
nerve to the brain
• Blind spot – located on the retina where the optic nerve
exists, there are no photoreceptors present
the signal proceeds to the optic chiasma
• Nerves from both eyes come together and some cross to
opposite sides of the brain
• allow for binocular vision (3-D)
• left and right visual fields cross to opposite hemispheres
(occipital lobe)
Signal enters the primary visual cortex (information is not
interpreted)
visual association area interprets image information and
flips/rotates image
http://www.youtube.com/watch?v=Q
ALdBU670Ro
http://www.benbest.com/science/anatmind/anatmd5.html
http://cti.itc.virginia.edu/~psyc220/
d. Vision defects

glaucoma – increase in
vitreous humor causes
the pressure to
collapse in the blood
vessel in the retina, no
nutrients and oxygen
are available and
blindness results

http://www.youtube.com/watch?v=c
F0rj4fM1l0&feature=related
http://www.springereye.com/glaucoma.html
cataract – lens/cornea becomes clouded
due to the degeneration of protein
structure
http://www.prof-vision.com/cataracts.html
astigmatism – lens/cornea is irregular,
focus is not sharp (light rays do not meet
at the correct focal point)
http://www.lasersurgeryforeyes.com/astigmatism.html

near sightedness
(myopia) – the lens is
elongated, the image
focuses in front of
retina, so it is difficult
to see objects far
away
 - the lenses worn to
correct myopia are
concave
http://hcd2.bupa.co.uk/fact_sheets/html/myopia.html
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far sightedness (hyperopia) –
the image focuses behind the
retina, so it is difficult to see
objects close up
- convex lenses correct
hyperopia
Lasik surgery
http://www.youtube.com/watch
?v=a7VRghAtwXU
http://www.youtube.com/watch
?v=GaoA4PLb7hc&feature=rel
ated
http://www.youtube.com/watch
?v=7PJ391MDtpo&feature=rel
ated
http://www.doctorergo.com/home.html?main=consumer/refractive.html
 color blindness –
occurs when one or
more type of cone is
defective (red-green),
defect is genetic and
occurs more often in
males than in females
http://www.eyecaresource.com/conditions/color-blindness/
Eye floaters
 http://www.youtube.com/watch?v=bscDeT
4tV9g&sns=em
The Eye video (24 min)
 http://www.accesslearning.com/videodetail
.cfm?asset_guid=599B05FF-4640-4B578C41-9CF68CE5479F
The Eye dissection
 http://www.bing.com/videos/search?q=eye
+dissection+&FORM=HDRSC3#view=det
ail&mid=801D48D547AD109F9FAB801D4
8D547AD109F9FAB
7. Ear
a. Outer Ear
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pinna (auricle)– the external ear flap collects sound
auditory canal – carries sound to the eardrum, is lined with
specialized sweat glands (ceruminous glands) that produce
earwax to trap foreign invaders
Tympanic membrane (eardrum) – membrane that converts
sound waves into mechanical motion (amplifies the sound) and
transmits the sound to the middle ear
• Separates outer and middle ear
http://www.entnet.org/healthinfo/ears/swimmers.cfm
b. Middle Ear
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ossicles – tiny bones which amplify and carry sound
(malleus/hammer, incus/anvil, stapes/stirrup)
oval window – receives sound waves from the ossicles. The
stirrup touching on the membrane passes on to cochlea
Eustachian tube – air filled tube connected to the throat which
equalizes pressure between inner and outer ear
http://www.oticon.com/eprOtiScripts/Files/encyclopedia/dir.asp?selectedID=198
c. Inner Ear

vestibule – connected by oval window, concerned with static
equilibrium (position of head, movement along one plane)
• utricle and saccule establish head position
• Contain otoliths which move due to force of gravity
• Causes fluid in the vestibule to move and the stereocillia to
bend
• Action potential is sent via the auditory nerve
• Brain adjusts body to maintain balance
http://paperairplane.mit.edu/16.423J/Space/SBE/neurovestibular/NeuroVestibular/2_Physiology/PhysSub2.html
c. Inner Ear

semicircular canals – movement of fluids here help identify
body movement (dynamic equilibrium)
• The base of each canal has an ampulla
• Inside the ampulla are stereocillia embedded in gelatinous
material (endolymph)
• Change in position causes the fluid to flow within the
ampulla, resuting in the stereocillia bending
• Nerve impulses relay information to the brain about body
position and motion
• http://www.youtube.com/watch?v=u84_BfK3hcw&feature=related
• http://www.youtube.com/watch?v=mmBB2bu1gEQ&feature=related
c. Inner Ear
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cochlea – used for hearing, this is where mechanical energy of
sound is converted to electrochemical impulses that are
transmitted to the brain
The inner ear is filled with fluid and vibrations in the oval window
are converted to pressure waves in the fluid
The cochlea can be divided into the organ of Corti, the basillar
membreane and the tectorial membrane.
• organ of Corti - the organ of hearing
• basilar membrane – on the base of the organ of Corti,
sensory mechanoreceptors called hair cells are found here
• the hair cells have projections called stereocillia
• the stereocillia are embedded in the tectorial membrane
round window – lets vibrations out and controls pressure in the
cochlea
http://www.oticon.com/eprOtiScripts/Files/encyclopedia/dir.asp?selectedID=198
d. Hearing
• sound waves push against eardrum
• vibrations are passed on to three bones (hammer, anvil, and stirrup) and
these bones in a lever system amplify vibrations
• oval window is pushed inward by vibrations
• round window pushes out to let vibrations out
• the movement of the oval window creates pressure waves in the fluid of
the cochlea
 The pressure waves make the basillar membrane move up and
down
 The stereocillia of the hair cells bend against the tectorial
membrane
 The hair cells synapse with the neve fibres of the auditory nerve
• signal is sent to the brain via the auditory nerve (auditory nervebrain
stemthalamustemporal lobe)
• http://www.youtube.com/watch?v=vTiGskc1o48
• (hearing and balance)
Frequencies of Sound
 The
hair cells of the organ of Corti are able
to distinguish frequency (pitch) and
amplitude (intensity) of sound waves

Different areas are sensitive to different
frequencies
• High frequencies stimulate the hair cells closest to
the oval window
• Low frequencies stimulate the hair cells farthest
from the oval window
• http://www.youtube.com/watch?v=2G9Q-r2leyw&feature=related
•
The Human Hearing Range
Hearing Loss
 Hearing
loss results from nerve damage or
damage to the conduction system of the
outer or middle ear
 Repeated or sustained exposure to loud
noise destroys the stereocillia
(permanently)
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Any noise about 80 decibels can do this
http://www.youtube.com/watch?v=j_Z-ylTtRts&feature=fvw
tubes
http://www.youtube.com/watch?v=1EJ4g3J6cJM&feature=related flintstones clip
http://www.accesslearning.com/videodetail.cfm?asset_guid=c3223b0d-c9a0-442e-8bdf6513b746596d hearing damage
Aiding Hearing Loss
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Hearing aids can amplify sound (helps people
with conduction deafness)
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http://www.youtube.com/watch?v=yQ17csWENEo&feature=related
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For people with nerve deafness, a device can be
implanted into the ear to pick up sounds and
directly relay them to the auditory nerve
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http://www.youtube.com/watch?v=-WA7-k_UcWY&feature=related
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Researchers are trying to find ways to
regenerate damaged hair cells