Health Occupations

Special Senses

Functions of our special senses Allows human body to react to environment Enables the body to

– See– Hear– Taste– Balance– Smell

Can occur because body has structures that– Receive sensation– Nerves that carry sensory messages to brain– Brain that can interpret & respond to message

Eye

Organ that controls sight Eye

– Receives light rays– Transmits rays to optic nerve– Optic nerve carries rays to brain– Brain interprets rays as vision or sight

Protection of eye Bony socket of skull

– Partially enclosed Eye lids & lashes

– Help keep out dirt & pathogens Lacrimal glands

– Produce tears which moisten & cleanse eye– Tears flow across eye, drain through lacrimal duct into nasal

cavity Conjunctiva

– Mucous membrane that protects eye– Lines eyelids & covers front of eye– Provides protection & lubrication

3 main layers of eye

Sclera– Outermost layer– Tough connective tissue– White of eye– Maintains eye shape– Extrinsic muscles

• Responsible for moving eye in socket• Attach to outside of sclera

– Cornea• Circular transparent part on front of sclera• Allows light rays to enter eye

3 main layers of eye

Choroid coat– Middle layer of eye– Interlaced with many blood vessels that nourish

eye– Pupil

• Hole in front of choroid coat• Allows light rays in

– Iris• Colored part of eye• Muscle that controls the size of the pupil & regulates

amount of light entering eye

3 main layers of eye

Retina– Innermost layer– Made of many layers of nerve cells that transmit

light to the optic nerve– 2 types of cells in retina

• Cones – Used for light vision– Sensitive to color– Located in depression on back of retina (FOVEA

CENTRALIS) which is the area of sharpest vision

• Rods– Used mainly for dim or dark vision

Other special structures

Lens– Circular structure behind pupil– Suspended in place by ligaments– Refracts (bends) light rays so that the rays

will focus on the retina

Aqueous humor

Clear watery fluid found in anterior chamber of eye

Fills space between cornea & iris Helps maintain forward curvature of

eyeball Bends (refracts) light rays

Vitreous humor

Jelly like substance found in posterior chamber of eye

Fills area behind lens Helps maintain eyeball shape Also bends or refracts light rays

1. Ciliary body & muscle2. Suspensoryligament3. Conjunctiva

4. Iris

5. Pupil

6. Path of light

7. Cornea

8. Lens

9. Suspensory ligament

Posterior chamber (vitreous humor)

11. Sclera

12. Choroid coat

13. Optic nerve

14. Fovea centralis

15. Retinal arteriesAnd veins

16. Retina

17. AnteriorChamber (aqeuous humor)

Refraction of light rays As light enters eye, it passes through a series of parts

that refracts it Rays pass through cornea, aqeuous humor, pupil, lens, &

vitreous humor Focus on fovea centralis, the area of retina that has

sharpest vision and the most nerve cells In retina, rays are picked up by rods & cones

– Changed into nerve impulses– Transmitted by the optic nerve to the occipital lobe of cerebrum– Sight can be interpreted by cerebrum

If rays are not refracted correctly, vision is distorted or blurred

Abnormal eye conditions

Amblyopia– Lazy eye– Common in early childhood– Results in poor vision in one eye

• Due to dominance in other eye

– Treatment• Cover good eye to stimulate development of lazy eye• Exercises to strengthen weak eye

– If untreated before 8-9 years of age• Blindness of weak eye may occur

Astigmatism

Abnormal shape or curvature of cornea Causes blurred vision To correct, apply corrective lenses Light rays focus on multiple areas of

retina

Cataracts

Normally clear lens becomes cloudy or opaque

Occurs gradually, usually result of age May be caused by trauma Symptoms

– Blurred vision– Halos around lights– Gradual vision loss– Milky white pupil in late stages

Cataracts

Treatment– Surgical removal of lens– Implant intraocular lens– New glasses or contacts

Conjunctivitis

Pink eye Contagious inflammation of conjunctiva Causes – bacteria or virus Symptoms

– Redness– Swelling– Pain– Pus formation

Treatment– Antibiotics, usually ointment

Glaucoma Results from increased intraocular pressure Caused by excess aqueous humor in anterior chamber of

eye Common after age 40 Leading cause of blindness Tonometer – instrument used to measure IOP, used

during every eye exam Symptoms

– Loss of peripheral vision– Halos around lights– Limited night vision– Mild aching

Glaucoma treatment

Controlled with meds – Decrease amount of aqueous humor– Improve drainage of aqueous humor

Surgery to create an opening for the flow of aqueous humor

Hyperopia

Farsightedness Light focuses behind retina Can see far away NOT near Correct with glasses or contacts -

convex

Myopia

Nearsightedness Light rays are refracted too sharply &

focus in front of retina Can see near NOT far away Corrected by concave lenses Can correct with surgery or lasers

Presbyopia

Farsightedness Caused by loss of lens elasticity Occurs as a result of normal aging Treated with reading glasses

Strabismus

Eyes do not focus or move together Eyes may be cross-eyed inwardly, outwardly,

or up & down Caused by muscle weakness in one or both

eyes Treatment

– Eye exercises– Covering good eye– Corrective lenses– Surgery on muscles moving eye

Ear

Organ that controls hearing & balance 3 main sections – outer, middle, inner Hearing

– Transmits impulses from sound waves to auditory nerve (vestibulocochlear)

– Auditory nerve carries impulses to brain– Brain interprets as hearing

Outer ear Auricle or pinna

– Visible part of ear– Elastic cartilage covered by skin– Leads to canal called the external auditory meatus and auditory

canal Auditory canal

– Contains special ceruminous glands producing cerumin (wax) for protection

– Sound waves travel through this to reach tympanic membrane Tympanic membrane

– Separates external & middle ear– Vibrates when sound hits it– Transmits sound waves to middle ear

Middle Ear Small space or cavity in temporal bone Contains 3 small bones (ossicles)

– Malleus– Incus– Stapes

Bones connected & transmit sound waves from tympanic membrane to inner ear

Eustachion tube– Tube connecting middle ear to pharynx that allows air to

enter the middle ear– Helps to equalize pressure on both sides of tympanic

membrane

Inner ear Most complex part of ear Oval window

– Membrane separating inner & middle ear Vestibule

– First section acting as entrance to 2 other parts of inner ear Cochlea

– Snail shaped – Contains delicate hair like cells that make up ORGAN OF

CORTI– Receives sound waves & transmits impulses to auditory

nerve

Inner ear

Semicircular canals– Contain liquid & hair like cells– Bend when liquids move with head & body

movements– Impulses sent to cerebellum to help

maintain balance & equilibrium

2. External auditory canal

1. Not pictured Pinna or auricle

3. Tympanic membrane

4. Malleus 5. Incus

6. Stapes

7. Semicircularcanals

8. Auditory nerve

9. Cochlea

10. Ovalwindow

11. Eustachiontube

Abnormal conditions

Hearing loss – 2 types– Conduction

• Caused by sound waves not being conducted to inner ear• Causes

– Cerumen plug– Foreign body obstruction – Otosclerosis– Infection– Ruptured tympanic membrane

• Treatment– Eliminate cause– Surgery– Hearing aids

Sensory hearing loss

Caused by damage to inner ear or auditory nerve

Usually can NOT be corrected Cochlear implants can improve severe

hearing loss

Meniere’s disease Collection of fluid in labyrinth of the inner ear &

degeneration of hair cells in cochlea & vestibule Symptoms

– Severe vertigo or dizziness– Tinnitus (ringing in ears)– N&V– Loss of balance & tendency to fall

Treatment– Drugs to reduce fluids & antihistamines– Drainage of fluid– Surgery to destroy cochlea in severe cases (causes

permanent deafness)

Otitis externa

Inflammation of external auditory canal Variety of causes

– Swimmer’s ear– Inserting foreign objects (bobby pins, fingernails,

cotton swabs)

Treatment– Antibiotics– Warm moist compresses– Pain meds

Otitis media Inflammation or infection of middle ear Causes – bacteria or virus Frequently follows sore throat because organisms

can enter ear through Eustachion tubes Susceptible –

– Infants & young children– Eustachion tube is angled differently than in adults &

secretions from nose & throat accumulate in middle ear– This causes inflammatory response that causes tube to

swell shut

Otitis media

Symptoms– Severe pain– Fever– Vertigo– Dizziness– N & V– Buildup of fluid in middle ear

Treatment– Antibiotics & pain meds– Myringotomy & tubes

Otosclerosis

Stapes becomes immobile & causes conductive hearing loss

Symptoms– Gradual hearing loss– Tinnitus– vertigo

Treatment– Surgical removal of stapes– Insertion of artificial stapes

Taste

Dependent on taste receptors located on tongue– Tongue is mass of muscle tissue with projections

called papillae– Papillae contain taste buds which are stimulated by

flavors & moistened by saliva Four main tastes

– Sweet & salty – tip of tongue– Sour – sides of tongue– Bitter – back of tongue

Influenced by smell

Smell

Nose is organ Determined by olfactory receptors in upper

part of nasal cavity Impulses from receptors are carried to brain

by olfactory nerve Sense of smell closely related to taste

– Smell much more sensitive– Human nose can detect over 6,000 different

smells

Skin & general senses

General sense receptors for pressure, heat, cold, touch, & pain located throughout body in skin & connective tissue

Each receptor perceives only 1 type of sense Messages from receptors allow human body

to respond to environment Helps body to react to conditions that could

cause injury