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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Stimulating Sensory Receptors

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 3

Other Important Eye Structures Include:

• Choroid LayerMiddle 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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Other 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.

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Light-Sensitive Rods

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Retinal Cells• Light-Sensitive Cells

• Rods: Respond to low-intensity 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 red-green. 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) 15

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The Sequence of Vision1. 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. 17

The Sequence of Vision4. 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•Automatic adjustments of the curvature of the lens by contraction of ciliary muscles to bring light intosharp focus on the retina

•Thick lens for close objects– ciliary muscles relax

•Thin lens for distant objects – ciliary muscles contract

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DEMO

Vision and The CNS

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Vision DefectsMyopia –

nearsightedness(inability to bring distance objects into focus)

Hyperopia – farsightedness

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. 23

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.

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Disorders video

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

Ear Structure• 3 Sections– 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. 31

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.

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The piston action of the stapes moves the fluid in the cochlea. This causes a vibration wave to travel down the basilar membrane.

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

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The piston action of the stapes moves the fluid in the cochlea. This causes a vibration wave to travel down the basilar membrane.

Hearing

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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)

Hearing

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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

Organ of Corti

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• 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 animation38

• http://www.freehearingtest.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

• Movement along one plane, such as vertical or horizontal (head position)

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

Dynamic Equilibrium• Movement along all planes.

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

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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Practice1. 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.

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)47

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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