Health Occupations
Special Senses
Functions of our special senses
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Allows human body to react to environment
 Enables the body to
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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
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– Receives light rays
– Transmits rays to optic nerve
– Optic nerve carries rays to brain
– Brain interprets rays as vision or sight
Protection of eye
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Bony socket of skull
– Partially enclosed
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Eye lids & lashes
– Help keep out dirt & pathogens
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Lacrimal glands
– Produce tears which moisten & cleanse eye
– Tears flow across eye, drain through lacrimal duct
into nasal cavity
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Conjunctiva
– Mucous membrane that protects eye
– Lines eyelids & covers front of eye
– Provides protection & lubrication
3 main layers of eye
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Sclera
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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
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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
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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
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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
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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
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2. Suspensory
ligament
3. Conjunctiva
4. Iris
1. Ciliary body & muscle
5. Pupil
6. Path of light
17. Anterior
Chamber
(aqeuous humor)
16. Retina
15. Retinal arteries
And veins
14. Fovea centralis
13. Optic
nerve
7. Cornea
12. Choroid
coat
8. Lens
11. Sclera
9. Suspensory ligament
Posterior chamber (vitreous humor)
Refraction of light rays
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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
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If rays are not refracted correctly, vision is
distorted or blurred
Abnormal eye conditions
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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
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Cataracts
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Normally clear lens becomes cloudy or
opaque
 Occurs gradually, usually result of age
 May be caused by trauma
 Symptoms
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Blurred vision
Halos around lights
Gradual vision loss
Milky white pupil in late stages
Cataracts
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Treatment
– Surgical removal of lens
– Implant intraocular lens
– New glasses or contacts
Conjunctivitis
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Pink eye
 Contagious inflammation of conjunctiva
 Causes – bacteria or virus
 Symptoms
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Redness
Swelling
Pain
Pus formation
Treatment
– Antibiotics, usually ointment
Glaucoma
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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
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Loss of peripheral vision
Halos around lights
Limited night vision
Mild aching
Glaucoma treatment
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Controlled with meds
– Decrease amount of aqueous humor
– Improve drainage of aqueous humor
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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
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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
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Presbyopia
Farsightedness
 Caused by loss of lens elasticity
 Occurs as a result of normal aging
 Treated with reading glasses
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Strabismus
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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
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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
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– Transmits impulses from sound waves to
auditory nerve (vestibulocochlear)
– Auditory nerve carries impulses to brain
– Brain interprets as hearing
Outer ear
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Auricle or pinna
– Visible part of ear
– Elastic cartilage covered by skin
– Leads to canal called the external auditory meatus
and auditory canal
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Auditory canal
– Contains special ceruminous glands producing
cerumin (wax) for protection
– Sound waves travel through this to reach tympanic
membrane
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Tympanic membrane
– Separates external & middle ear
– Vibrates when sound hits it
– Transmits sound waves to middle ear
Middle Ear
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Small space or cavity in temporal bone
 Contains 3 small bones (ossicles)
– Malleus
– Incus
– Stapes
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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
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Most complex part of ear
 Oval window
– Membrane separating inner & middle ear
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Vestibule
– First section acting as entrance to 2 other parts of
inner ear
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Cochlea
– Snail shaped
– Contains delicate hair like cells that make up
ORGAN OF CORTI
– Receives sound waves & transmits impulses to
auditory nerve
Inner ear
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Semicircular canals
– Contain liquid & hair like cells
– Bend when liquids move with head & body
movements
– Impulses sent to cerebellum to help
maintain balance & equilibrium
1. Not pictured
Pinna or auricle 4. Malleus 5. Incus
7. Semicircular
canals
8. Auditory nerve
9. Cochlea
2. External auditory canal
10. Oval
window
3. Tympanic
membrane
6. Stapes
11. Eustachion
tube
Abnormal conditions
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Hearing loss – 2 types
– Conduction
• Caused by sound waves not being conducted to inner
ear
• Causes
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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
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Meniere’s disease
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Collection of fluid in labyrinth of the inner ear
& degeneration of hair cells in cochlea &
vestibule
 Symptoms
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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
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Inflammation of external auditory canal
 Variety of causes
– Swimmer’s ear
– Inserting foreign objects (bobby pins, fingernails,
cotton swabs)
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Treatment
– Antibiotics
– Warm moist compresses
– Pain meds
Otitis media
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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
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Symptoms
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Severe pain
Fever
Vertigo
Dizziness
N&V
Buildup of fluid in middle ear
Treatment
– Antibiotics & pain meds
– Myringotomy & tubes
Otosclerosis
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Stapes becomes immobile & causes
conductive hearing loss
 Symptoms
– Gradual hearing loss
– Tinnitus
– vertigo
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Treatment
– Surgical removal of stapes
– Insertion of artificial stapes
Taste
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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
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Four main tastes
– Sweet & salty – tip of tongue
– Sour – sides of tongue
– Bitter – back of tongue
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Influenced by smell
Smell
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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
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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