Stimulating Sensory Receptors
Types of sensory receptors:
• 1. Chemoreceptors: Sense specific chemicals.
eg.(taste buds, lining of the nasal cavity = olfactory
receptors, internal receptors like blood pH)
• 2. Photoreceptors: Sense visible light. eg. (eye)
• 3. Thermoreceptors: Sense temperature eg. (skin)
• 4. Proprioreceptors: Sense stretching in muscle
fibers, ligaments, and tendons.
• 5. Mechanoreceptors: Sense changes in
pressure/touch/pain eg. (finger tips, hearing,
balance, body position)
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The Eye
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The Eye is Comprised of 3 Layers:
• Sclera
– The outermost layer of the eye.
– Protectively layer
– Maintains the eye’s shape
• Cornea
– Acts as a window to the eye by
refracting light toward to pupil.
– Protects eye
– Does not receive blood supply
– Does require oxygen and
nutrients.
• Retina 
– inner layer, covers 65% of inner
surface, site of all light receptors
– Translates light stimuli into nerve
impulses
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Other Important Eye Structures Include:
• Choroid LayerMiddle layer
– **Absorbs light
– **Contains the blood vessels that nourish the retina with
oxygen and nutrients.
• Iris
– Thin circular muscle that acts as a diaphragm , controlling the
size of the pupil.
– Opening formed by the iris lets light into the eye.
• Lens
– Focuses the image on the retina
– Found immediately behind the iris.
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her Important Eye Structures Include:
• Aqueous Humour
– The transparent fluid in the chamber
behind the cornea.
• Ciliary Muscles
– Attached to both end of the lens;
therefore, can alter its shape.
• Vitreous humour
– Chamber that is behind the lens
– Cloudy, jelly-like material
– Maintains shape of the eye and
permits light transmission to the
retina.
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Eye Movement
• How Does the Eye Move?
• Extrinsic muscles attach to the sclera and
move the eye up, down, side to side
• Intrinsic Muscles: Control lens and iris and are
controlled by the ANS. You have two sets ,
one for contracting and one for dilating
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The Retina
• Innermost layer of the eye
• 4 layers of cells:
•
•
•
•
Pigmented Epithelium Cells
Light-Sensitive Cells
Bipolar Cells
Optic Nerve Cells
• In the center of the retina
there is a tiny depression
called fovea centralis. This
is the most sensitive area
of the eye.
Light-Sensitive Rods
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Retinal Cells
• Light-Sensitive Cells
• Rods: Respond to lowintensity light
• Cones: high intensity light
and identify color.
*These are “sensory receptors”
• Bipolar Cells
• Relay the message from the
rods/cones to the optic
nerve.
• Optic Nerve
• Carries the impulse to the
CNS.
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Fovea Centralis
•It contains cones that are packed very closely together.
•Rods are found surrounding the fovea.
***There are 125 million rods and 6 million cones in your retina
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Blind Spot
•This is the area where the optic nerve comes in contact with the retina.
•There are no rods or cones located here.
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Chemistry of Vision: Rods
• Rods contain a light-sensitive
pigment called rhodopsin
• Cones contain similar pigments,
but they are less sensitive to light.
• When a light strikes a rhodopsin
molecule, it divides into two
components; retinene- the
pigment portion & opsin- the
protein portion.
• This division alters the cell
membrane and produces an
action potential.
• In bright light, rhodopsin breaks
down faster than it can be
restored; vision is in shades of
grey.
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Chemistry of Vision: Cones
• Cones are responsible for
color vision.
• Each cone is sensitive to
one of the 3 primary colors
(red, blue and green).
• When combinations are
cones are stimulates, the
brain perceives different
colors.
– For Example: To see the color
yellow means that cones
sensitive to both green and red
wavelengths were stimulated.
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Color Blindness
• Occurs when one or more
types of cones are
defective.
• Most common type is redgreen. Occurs when cones
containing the red-sensitive
pigments fail to work
properly.
• This is a genetic defect and
is more common in males
(we will discuss why in
genetics)
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The Sequence of Vision
1. Rays of light enter the eye
through the cornea, where
they are partly bent
(refracted).
2. The rays of light then pass
through the transparent
lens, which changes shape
in order to fine-focus the
image (accommodation).
3. The light continues
through the fluid matter,
vitreous humor, with in
the eyeball and shines an
upside-down image onto
the retina lining.
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The Sequence of Vision
4. The rods and cones of the
retina, convert the light
energy that falls on them
into nerve impulses (action
potentials).
5. Nerve fibers that extend
from the rods and cones
and attach to neurons that
are connected to the optic
nerve.
6. The optic nerve will direct
the impulse to the
necessary vision areas in
the CNS.
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Accommodation
DEMO
•Automatic adjustments of
the curvature of the lens by
contraction of ciliary
muscles to bring light into
sharp focus on the retina
•Thick lens for close
objects– ciliary muscles
relax
•Thin lens for distant
objects – ciliary muscles
contract
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Vision and The CNS
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Vision Defects
Myopia – nearsightedness
(inability to bring distance objects into focus)
Hyperopia – farsightedness
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Astigmatism
• Astigmatism can be caused
by the lens of the eye but it
is most often described as
resulting from an irregular
curvature of the cornea of
the eye.
• The most common
symptom of astigmatism is
blurred vision. Some people
describe it as double vision
but in only one eye.
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Laser Eye Surgery
• Is alternative to wearing contact
lenses of glasses.
• Treatment for myopia, hyperopia, and
astigmatism.
• The operation is performed with the
patient awake and mobile; however,
the patient is sometimes given a mild
sedative and eye drops.
• LASIK is performed in three steps. The
first step is to create a flap of corneal
tissue. The second step is remodeling
of the cornea underneath the flap
with the laser. Finally, the flap is
repositioned.
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Glaucoma
•Glaucoma is
abnormally high
pressure inside the sys
due to a buildup of
fluid.
•The pressure my
permanently damage
nerve fibers in the
retina or optic nerve
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Cataracts
•The normal
transparent lens of the
eye is cloudy as a
result of changes in
the protein fibers in
the lens.
•This cloudiness,
reduces the clarity of
images.
•Generally, are apart
of the aging process.
Disorders video
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Video Links:
• How the Eye Works
• Carrots and Eye Sight?
• The Eye: Vision and
Perception
• Discovery: The Human
Body
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joke
• What do you call a wet
comedian ?
• Aqueous humour
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The Ear
Functions: Hearing and Equilibrium
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• 3 Sections
Ear Structure
– Outer Ear
– Middle Ear
– Inner Ear
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The Outer Ear
• Pinna:
• The external ear flap,
which collects the
sound.
• Auditory Canal:
• Carries sound waves
to the eardrum.
• Lined with specialized
sweat glands that
produce earwax
(traps foreign
particles)
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The Middle Ear
• Tympanic Membrane:
– Thin layer of tissue that receives
sound vibrations (eardrum).
• Ossicles:
– Tiny bones that amplify and carry
sound vibrations.
• Malleus (hammer)
• Incus (anvil)
• Stapes (stirrup)
• Eustachian Tube:
– Air-filled tube of middle ear that
equalizes pressure between the
external and internal ear.
– Extends from ear, mouth and
nose.
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The Inner Ear
• Vestibule:
– Chamber found at the base of
the semicircular canals that
provides information about
static equilibrium.
– Houses 2 small sacs, the
utricle and saccule, which
establish head position.
– Oval Window: oval shaped
hole in the vestibule, covered
by a thin layer of tissue.
The piston action of the stapes moves
the fluid in the cochlea. This causes a
vibration wave to travel down the basilar
membrane.
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The Inner Ear
• Semicircular Canals:
– Fluid-filled structures that are
arranged at different angles.
– Movement of the fluid in the
canals helps you identify body
movement.
• Cochlea:
– Coiled structure that contains
rows of specialized hair cells.
The hair cells respond to
sound waves and convert
them into nerve impulses.
– Organ of Corti– organ of
hearing
The piston action of the stapes moves
the fluid in the cochlea. This causes a
vibration wave to travel down the basilar
membrane.
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Hearing
1. The pinna collect sound waves and send them down auditory
canal
2. Sound vibrations cause the tympanic membrane (eardrum) to
vibrate (*sound waves are converted into mechanical energy)
3. The movement of tympanic membrane causes the ossicles (3
tiny bones) to move concentrating the vibrations on the oval
window in the inner wall of middle ear (vestibule)
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Hearing
4. The vestibule is attached to a snail-shaped structure
called the cochlea (fluid filled). The fluid in cochlea
moves and causes movement of tiny cilia (hairs) in the
Organ of Corti
5. The cilia are mechanoreceptors and cause
depolarization of auditory nerves
6. Nerve impulses are sent to the temporal lobe of brain
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Organ of Corti
• Comprised of
a single inner
row and
three outer
rows of
specialized
hair cells.
• Anchored to
the basilar
membrane.
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Identifying Pitch and Loudness
• Identifiable because of the cochlea
• Close to the oval window, the basilar membrane
is narrow and stiff.
– Activated by high-frequency sound waves
– Energy high enough to move the membrane, which in turn causes
the hair cells to move.
– Hair cell movement triggers an action potential, which is carried
to the brain and understood as a high pitch sound.
• Further in the cochlea, the membrane widens
and becomes more flexible.
• Sound waves in the cochlea animation
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• http://www.freehearing
test.com/test3.shtml
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Deafness
• Conductive Deafness:
• Problem with sound conduction
through outer and middle ear
(physical blockage of ossicles
movement)
• Corrected by hearing aid: sound
waves are amplified by electrical
speaker
• Sensorineural Deafness:
– Problem with receptor cells or
sensory nerve due to exposure to
high amplitude sound which
damages hair cells in the cochlea.
• Corrected with cochlea
implants which convert sound
to electric signal.
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Balance and Equilibrium
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Balance (Equilibrium)
Static Equilibrium
Dynamic Equilibrium
• Movement along one plane, such
as vertical or horizontal (head
position)
• Movement along all planes.
1. When head position changes, fluid
in saccule and utricle causes
calcium carbonate crystals
(otoliths) to move
2. This movement causes tiny cilia to
bend
3. Trigger nerve impulses sent to
cerebellum for interpretation via
the vestibular nerve
1. When the body moves, fluid in
the semicircular canals move.
(There are 3 canals positioned in
3 different planes)
2. The fluid moves tiny cilia which
initiates depolarization of
adjacent neurons
3. A nerve impulse travels down
nerves to the cerebellum via the
vestibular nerve
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Video
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Vertigo
• A false sensation of movement
and a spinning sensation are
often associated with nausea
and sometime serve vomiting.
• Result of disturbances in the
inner ear or areas of the brain
concerned with balance.
• Develops suddenly and can last
a few seconds or several days.
Can occur be intermittently or
constant.
• Can make it impossible to walk
of stand.
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Practice
1. What function do the tympanic membrane, ossicles, and oval window
serve in sound transmission?
2. Categorize the following structures of the inner ear according to whether
their functions relate to balance or hearing: organ of Corti, cochlea, vestibule,
saccule, semicircular canals, oval window.
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Skin Receptors
• Skin receptors
include: touch, heat,
pressure, and pain.
• The brain is what
registers and
interprets the
sensation.
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Taste Receptors
• Taste receptors found on the
tongue (taste buds)
• Chemicals dissolve in saliva and
stimulate receptors in taste buds
• 5 main types of taste:
– sweet, sour, salt, bitter and savory
• Each taste is associated with the
molecular structure and charges on
the food molecules
• For Example:
– Sodium chloride ions – salty
(potatoes chips)
– Monosodium glutamate- savory
(Asian food)
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Taste and Smell
• Both taste and smell (olfaction)
work closely together.
• For Example:
– When your nose is clogged do you
have difficulty tasting food?
– This is b/c your olfactory cells are
less effective
– Reduced taste a result of needing
both receptors.
• Nose: detects air borne
chemicals
• Tongue: detects dissolved
chemicals
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