The Eye 1” in diameter Protected by orbital socket of skull, eyebrows, eyelashes and eyelids

Bathed in fluid from LACRIMAL GLANDS – tears empty into nasal cavity

The human eye can detect a lighted candle 1 mile away Humans blink about 15 times a minute

CONJUNCTIVA thin membrane that lines the eyelids and covers part of the eye, secretes mucous to lubricate eye

Wall of the eye made up of three coats

SCLERA Outer layer White of the eye Tough coating, helps maintain shape of eye and protects what’s inside Muscles responsible for moving the eye are attached to the sclera – called EXTRINSIC MUSCLES

CORNEA Front of sclera – clear part (no blood vessels) Transparent so light rays can pass through Gets O2 and nutrients through lymph Protects the eye and focuses light

CHOROID COAT Middle layer Contains blood vessels Opening in front is the PUPIL Colored, muscular layer surrounding pupil is IRIS INTRINSIC MUSCLES – change size of iris to control amount of light entering through the pupil

IRIS People often share the same eye color, but the precise pattern of pigment in their irises is as personal as a fingerprint. Security systems have been developed to recognize iris patterns, so that people can come and go without keys or special codes. Some people believe that a wide range of disorders can be diagnosed by examining the iris, but this procedure – called iridology – is not recognized by most doctors.

LENS Crystalline structure located behind iris and pupil Elastic, disc-shaped, biconvex Situated between the anterior and posterior chambers Provides fine focus control

ACCOMMODATION change in the shape of the lens to allow for near and distant vision

CHAMBERS ANTERIOR CHAMBER filled with AQUEOUS HUMOR, a watery fluid. POSTERIOR CHAMBER filled with transparent, jellylike substance – VITREOUS HUMOR

RETINA Innermost layer Light rays focus an image on the retina The image travels to the cerebral cortex via the OPTIC NERVE If light rays don’t focus properly on the retina, corrective lenses can bend the light rays as required. Retina contains specialized cells – rods and cones

RODS – sensitive to dim light CONES – sensitive to bright light and color OPTIC DISC – on the retina, known as the blind spot – nerve fibers gather here to form the optic nerve, no rods or cones A person can see up to 10,000 colors The retina contains about 106 million cells

Each eye gives a slightly different view of the world. The brain combines these views to provide a three-dimensional image

Pathway of Vision Cornea Pupil Lens (Where light rays are refracted) Retina Rods and Cones (pick up stimulus) Optic Nerve

The Ear Hearing and equilibrium 3 parts: Outer, middle and inner ear

EAR FACTS Humans can distinguish over 1,500 musical tones People can hear sounds ranging form 0 to 140 decibels Ears can detect the direction of sound within 3 degrees The smallest bone in the body is the stirrup Sounds above 130 dB can cause cellular damage to the ear and may lead to deafness

Outer Ear PINNA (AURICLE) – outer ear, collects sound waves EXTERNAL AUDITORY CANAL – ear canal

CERUMEN earwax, protects the ear Found in external auditory canal

TYMPANIC MEMBRANE ear drum, separates outer and middle ear

Middle Ear Cavity in temporal bone Connects with pharynx by EUSTACHIAN TUBE – which equalizes pressure in the middle ear with outside atmosphere

OSSICLES Bones in middle ear that transmit sound waves from ear drum to inner ear MALLEUS (hammer) INCUS (anvil) STAPES (stirrup)

Inner Ear Contains spiral shaped organ of hearing – the COCHLEA The cochlea contains a membranous tube, the cochlear duct – which is filled with fluid that vibrates when sound waves are transmitted by the stapes

ORGAN OF CORTI delicate hairlike cells that pick up vibrations of fluid and transmit them as a sensory impulse along the auditory nerve to the brain

SEMICIRCULAR CANALS Three structures in the inner ear, contain liquid that is set in motion by head and body movements – impulses sent to cerebellum to help maintain body balance (equilibrium).

Pathway of Hearing External Auditory Canal Tympanic Membrane Ossicles (malleus, incus & stapes) Cochlea Auditory nerve

The Nose Smell accounts for 90% of taste Tissue in the nose, olfactory epithelium, contains specialized nerve cell receptors. Those receptors stimulate the OLFACTORY NERVE to the brain.

SMELL FACTS The sense of smell can detect 2,000 – 4,000 different odors using around 20 million smell cells Sniffing draws molecules up to the smell receptors for analysis The brain grows used to smells quickly and stops registering them (habituation) The sense of smell is strongest at birth & helps a baby to recognize its mother

The Tongue Mass of muscle tissue Bumps on the surface are PAPILLAE, they contain the TASTE BUDS Receptors in taste buds send stimuli through 3 cranial nerves to the cerebral cortex

TASTE FACTS A baby has taste buds all over the inside of the mouth There are over 10,000 taste buds on the tongue Taste bud cells only last a week before being renewed. Sensitivity to taste decreases with age. Elderly people have about half the taste ability of babies, so some food can taste bland to them

Disorders of the Eye CONJUCTIVITIS Pink eye Inflammation of conjunctival membranes in front of the eye Redness, pain, swelling and discharge Highly contagious Rx – antibiotic eye drops

GLAUCOMA Excessive intraocular pressure causing destruction of the retina and atrophy of the optic nerve Caused by overproduction of aqueous humor, lack of drainage, or aging Symps – develop gradually – mild aching, loss of peripheral vision, halo around the light TONOMETER – measures intraocular pressure Rx – drugs or laser surgery

CATARACTS Lens of eye gradually becomes cloudy Frequently occurs in people over 70 Causes a painful, gradual blurring and loss of vision Pupil turns from black to milky white Rx – surgical removal of the lens

STY (HORDEOLUM) Abscess at the base of an eyelash (in sebaceous gland) Symps – red, painful and swollen Rx – warm, wet compresses

EYE INJURIES Tears are effective in cleaning the eye If glass or fragments get in eye, cover both eyes and see medical treatment. (DO NOT remove the object)

COLOR BLINDNESS cones are affected – genetic disorder that is carried by the female and transmitted to males Color blindness affects around 1 person in 30, but affects as many as 1 in 12 men

Vision Defects PRESBYOPIA Lens loses elasticity, can’t focus on close or distant objects Usually occurs after age 40 Rx - Bifocals

HYPEROPIA Farsighted Focal point beyond the retina because eyeball too short Convex lenses help

MYOPIA Nearsighted Eyeball too long Concave lenses help

ASTIGMATISM Irregular curvature of the cornea or lens, causing blurred vision and eye strain Rx – corrective lenses

DIPLOPIA double vision

STRABISMUS (cross-eyes) Eye muscles do not coordinate their actions Usually in children Rx – eye exercises or surgery

OPHTHALMOSCOPE instrument for viewing inside the eye

SNELLEN EYE CHART chart that uses letters or symbols in calibrated heights to check for vision defects

Disorders of the Ear Loud noise and hearing loss – hearing is fragile. Loud noise over a period of time can cause hearing loss. Symptoms – TINNITUS (ringing in ears) and difficulty understanding what people are saying

OTITIS MEDIA Infection of the middle ear Often a complication of a common cold in children Rx – antibiotics If chronic or if fluid builds up – MYRINGOTOMY (opening in the tympanic membrane) with tubes inserted will relieve the pressure

MYRINGOTOMY

OTOSCLEROSIS Chronic, progressive middle ear disorder Stapes becomes spongy and then hardens, becoming fixed and immobile Common cause of deafness in young adults Rx – stapedectomy and total replacement of stapes

TINNITUS ringing in the ears from impacted wax, otitis media, otosclerosis, loud noise, blockage of normal blood supply to the cochlea, drugs (salicylates)

PRESBYCUSIS deafness due to the aging process, can be helped with the use of hearing aids

Types of hearing loss: Conductive – which sounds are prevented from reaching inner ear Sensorineural – problem with inner ear or auditory nerve

Disorders of the Nose RHINITIS Inflammation of the lining of the nose with nasal congestion, drainage, sneezing and itching Caused by allergies, infection, fumes, odors, emotion, or drugs Rx – eliminate causes, antihistamines