http://faculty.washington.edu/chudler/chvision.html

I Senses of the body A. General sensory receptors are found all over the body.

1. Proprioceptors of muscles and joints. 2. Pressure, pain, touch, and temperature

receptors of the skin. 3. Special senses include the following with

special receptors/organs:

Hearing Taste Vision Smell Equilibrium

II The eye and vision (70% of all sensory receptors are in the eye)

A. Structures of the eye 1. Eyelashes – Prevent

debris from entering eye

2. Eyelids – Cover and protect the eye

3. Conjunctiva – Lines the eyelid and part of

the surface of the eyeball. Secretes mucus for lubrication.

4. Lacrimal Glands secrete the

dilute salt solution with enzymes and

antibodies,

5. Extrinsic eye muscles – Six muscles attached to the outer eye surface, responsible for gross motor movement of the eyeball.

6. Meibomian glands – specialized sebaceous glands to lubricate eye.

7. Ciliary glands – modified sweat glands between eyelashes for lubrication.

8. Eye ball – hollow sphere made from 3 tunics (coats) and is filled with a liquid (humors). Divided into two chambers by the lens.

a. Tunics i. Sclera – outermost layer, thick and white with a transparent center called the cornea (where light enters the eye).

ii. Choroid – blood rich nutritive tunic with a dark pigment (prevents light from scattering inside the eye). Forms the ciliary body and the iris (smooth muscles). Iris has a rounded opening – pupil – which regulates the amount of light entering the eye.

1. Ciliary body – attaches to the lens to modify shape

2. Iris – contracts and relaxes to control pupil size.

iii. Retina – Sensory tunic; location of cones (detects color) and rods (low levels of light, grays and peripheral vision). These receptor cells lead to sensory neurons that converge to form the optic nerve. 1. Blind spot – on the retina

where the optic nerve is found (no sensory receptors so no vision at this point)2. Fovea centralis – area lateral to each blind spot where the highest concentration of sensory receptors is located (area of highest visual acuity:reading, watching TV, driving)-center of the macula)

b. Humors i. Aqueous humor – in the anterior chamber of

the eye. Helps maintain intraocular pressure and provides nutrients for lens and cornea (they lack blood supply).

ii. Vitreous humor – in the posterior chamber of the eye. Gel like liquid used to prevent collapse of the eye.

B. Physiology of vision 1. Light waves travel towards the eye

and enter through the pupil. 2. The movement of the light waves

through the structures of the eye, bend the light rays (hopefully to focus directly on the retina). This is called refraction.

3. Depending on the distance of the object you are looking at, the lens must change shape (with contraction of ciliary body) to focus light waves on the retina.The ability to change and focus on objects at different distances is called accommodation. The image is also inverted as the light waves travel through the lens.

eye animation

Notice that the farther the image, the smaller the image on the retina.

4. Once the receptors have been stimulated, thereby changing the shape of pigment proteins in the cell, this change causes electrical changes creating the nerve impulse (Action potential!!).

5. The optic nerves from both eyes cross at the optic chiasma, which results in the left side of the brain receiving visual information from the right eye and vice versa.

6. Once the impulse has reached the occipital lobe, the visual information will be interpreted and understood by known visual information stored in that area of the brain. Ex. recognizing someone you have met before.

CAN see objects at close range but difficulty with distances

CAN see things far away but not up close

Lasik Eye surgery http://www.youtube.com/watch?

v=7PJ391MDtpo

Strabismus animationhttp://www.midwesteyecare.com/SubSection/index.php?SectionID=7&SubSectionID=170&ParentID=59

7. Eye muscle fatique – Internal and External muscles a. External muscles- responsible for

convergence – reflexive movement of the eyes medially (toward the center) when you view something close. Strabismus “crossed “ eyes is caused by unequal pulls by these muscles. (This is not the same thing as “lazy eye”, it is associated with strabismus and can result in decreased vision in the affected eye.) The muscles must be retrained. (If the eyes cannot be retrained a patient may choose to have surgery to realign the eyes)

7. b. Internal muscles – ciliary body constrict focusing lens and iris contracts reducing the size of the pupil. c. Over time these

muscles can become fatigued such as when you read for long periods of time. Take a break and look off in the distance to relax those muscles.

Cataracts- clouding of the lens of the eye

Glaucoma- increased intraocular pressure

2

9-gel-like fluid

8

5

6

7

3-transp

a4- muscle

that is attcached

to lens

1- fluid

10. choroid 11. lens 12. vitreous

humor 13. sclera 14. iris 15. retina 16. aqueous

humor

a. Controls the size of the pupil, colored part of the eye

b. Changes shapes to focus on objects by bulging when things are up close

c. The outermost tunic or coat of the eye, is white and protective

d. The nutritive layer of the eye, is darklyPigmented to prevent the scattering of light

e. The sensory tunic, contains rods and cones

f. gel- like fluid that fills the posterior chamber of the eye

g. The fluid that fills the anterior chamber of the eye, provides nutrients to cornea and lens

III Hearing and Equilibrium A. Mechanoreceptors are used which respond to physical forces (movement of liquid) to convey information on hearing and equilibrium. There are two different systems in the ear, one for hearing and one for equilibrium. B. Hearing

1. Anatomy of the ear a. External ear

i. Pinna or Auricle – external auditory meatus, gathers sound waves

and directs them down the canal.ii. External canal – (about 1

inch), conduct waves through the temporal bone.

iii. Ceruminous glands – secrete wax, contains antibodies and filters debris, also a deterrent for mosquitoes

iv. Tympanic membrane – vibrates when sound waves strike it and transmit vibrations to middle ear.

b. Middle ear (about the size of a dime)

i. Auditory tube – links middle ear with throat and helps to equalize pressure in middle ear. Typically is closed.

ii. Oval window – connects the stirrup (stapes) to the inner ear on cochlea.

iii. Ossicles 1. Hammer / malleus –

transmits vibrations of the eardrum to the next ossicle.2. Anvil / incus – second ossicle, transmits vibrations.3. Stirrup / stapes – transmits vibrations to cochlea.

c. Inner ear (bony chamber/labyrinth) –just behind eye orb.

i. Cochlea (contains the organ of corti) – location of hair cells (hearing receptors). Receives vibrations from oval window. Made up of vestibule and semicircular canals. Contains a fluid that transmits vibrations to auditory nerves

2. Pathway and mechanism of hearing – the journey of the vibration

3. Hearing Deficit Causes a. Conduction deafness – There is an

obstruction to the conduction of vibrations on the way to the organ of corti. Causes include ear infection, build up of wax in canal, fusion of ossicles, and ruptured eardrum. Hearing aids can help by sending the vibrations via the bone. b. Sensorineural deafness – Degeneration or damage to the receptor cells. Causes include over exposure to very loud sounds. No treatment.

C. Equilibrium 1. Monitored by the vestibular apparatus

(includes the vestibule and semicircular canals of inner ear). Help control balance with the cerebellum! Where are you in space or deep in the water?

2. Two different functions: a. Static equilibrium – receptors in

vestibule monitor the position of the head with respect to gravity when you are not moving. (i.e. – sitting in your chair and you turn your head to the side). When your head moves, the gel moves and triggers the hair cells sending the message to the brain via the 8th cranial nerve (vestibular).

b. Dynamic equilibrium – Receptors are in semicircular canals and respond to the circular movements of the head (ex. twirling on the dance floor, the movements of your body while on a boat in rough seas). The endolymph(fluid) within the semicircular canals moves opposite the direction that your body is moving, this motion shifts the cupula (gel like material) thereby stimulating the receptor hairs. Once stimulated the information about the movement of the head and body is transmitted to the brain via the vestibular nerve.

IV Chemical Senses – These receptors respond to specific chemicals in solution

A. Olfactory (smell) 1. Olfactory receptors are located in the roof of

each nasal cavity, there are 1000’s that each detect a different chemical odor. These receptors

are at the top of the nasal cavity, which is why “sniffing” intensified the smell, because more air is forced to the top of the cavity, stimulating the receptors. 2. The receptor cells have hairs on them (similar to equilibrium and hearing). They are bathed in a thick layer of mucus. As the olfactory chemicals diffuse through the mucus, they stimulate the receptors which send the message via the olfactory filaments to the olfactory nerve (CN I). 3. This pathway goes directly through the limbic system (emotional center), therefore there tends

to be strong emotional ties to smells. These receptors, like others, can adapt to stimuli that are constant, which is why women or men don’t

smell their own cologne or perfume after a period of time.

V Sense of Taste A. Receptors are called taste buds and there are over 10,000 located on the

tongue. Very few are located on your soft palate and the inside of your cheek.

1. There are 4 basic taste sensations: a. Sweet – respond to sugar,

saccharine, and some amino acids.

b. Sour – respond to H+ ions (acids)

c. Bitter – respond to alkaloids (basic)

d. Salty – respond to metal ions

2. The regions of the tongue don’t truly hold true, because the receptors are pretty well evenly distributed over the surface of the tongue.

B. Sense of taste and certain cravings help to satisfy homeostatic imbalances. When you crave carbohydrates or orange juice it can be your body’s way of communicating to your consciousness to fulfill these deficiencies.