Sensory System Unit- L

Special Senses 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) Conjunctiva – thin membrane that lines the eyelids and covers part of the eye.

The Eye Wall of Eye is made up of 3 layers or coats Sclera, Choroid Coat, and the Retina SCLERA- Outer layer White of the eye Tough, fibrous capsule helps maintain shape of eye and protects the structure within. EXTRINSIC MUSCLES- muscle responsible for moving the eye that are attached to the sclera.

The Other Eye Cornea – Front of sclerotic coat (part of sclera) Clear part (no blood vessels) – called the “window of the eye” Transparent so light rays can pass through Gets O2 and nutrients through lymph

I can see you…. Choroid Coat Middle layer Contains blood vessels Circular 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 – exposed to light = constriction

Can you see me?? Lens Crystalline structure located behind iris and pupil – focuses light rays on retina – function is accommodation = adjusting for near / far vision Elastic, disc-shaped, biconvex Situated between the anterior and posterior chambers

Both substances maintain eye’s spherical shape and refract light rays Hey…where did you go?? ANTERIOR CHAMBER filled with AQUEOUS HUMOR, a watery fluid. POSTERIOR CHAMBER filled with transparent, jellylike substance - VITREOUS HUMOR Both substances maintain eye’s spherical shape and refract light rays

Oh no!! It’s dark in here!! Retina Innermost layer – 3rd coat of the eye – located between the posterior chamber and choroid coat Light rays focus an image on the retina The image then travels to the cerebral cortex via the OPTIC NERVE. If light rays do not focus correctly on the retina, the condition may be corrected with properly fitted contact lenses, or eyeglasses, which bend the light rays as required.

Finally…the eye is almost over! Retina contains specialized cells, visual receptors - rods and cones RODS- sensitive to dim light…problems driving at night….damage to rods CONES – sensitive to bright light – responsible for color vision OPTIC DISC- on the retina, known as the blind spot- nerve fibers gather here to form the optic nerve, no rods or cones.

The Eye Pathway of Vision CORNEA PUPIL LENS (Light rays are refracted) RETINA

The Ear Outer Ear PINNA (AURICLE)- outer ear, collects sound waves EXTERNAL AUDITORY CANAL- ear canal CERUMEN- earwax, protects the ear TYMPANIC MEMBRANE- ear drum, separates outer and middle ear.

Can you hear me?? Middle Ear Cavity in temporal bone Connects with pharynx by EUSTACHIAN TUBE - which equalizes pressure in the middle ear with outside atmosphere. Bones in middle ear transmits sound waves from ear drum to inner ear. MALLEUS (hammer) INCUS (anvil) STAPES (stirrup)

I can hear you  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- in the cochlea - 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).

Where does the sound go? Pathway of Hearing Sound waves Pinna External Auditory Canal Tympanic Membrane Ossicles ( malleus, incus, & stapes) Cochlea Auditory nerve Brain

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

Common Sensory Disorders 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

Eye disorders Glaucoma Excessive intraocular pressure causing destruction of the retina and atrophy of the optic nerve Caused by over production 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 to decrease intraocular pressure

Common Sensory Disorders 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 Macular Degeneration Eye disorder that occurs with aging The macula ( part of the retina responsible for sharp color vision) degenerates Vision is reduced but usually doesn’t cause total blindness.

Still problems with the eye Detached Retina May occur with aging- accident can cause it at younger age Retina detaches from choroid Symps- loss of peripheral vision and then central vision Rx- laser or freezing technique 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) Night blindness = NYCTALOPIA- due to inactive rods Color blindness- cones are affected – genetic disorder that carried by the female and transmitted to males.

Eye doctor = Opthamologist Do you need glasses? PRESBYOPIA Lens loses elasticity, cant 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 – can’t see far away Eyeball too long Concave lenses help Eye doctor = Opthamologist

Still more eye problems AMBLYOPIA Reduction or dimness of vision ASTIGMATISM Irregular curvature of the cornea or lens, causing blurred vision and eye strain Rx- corrective lenses DIPLOPIA- double vision STABISMUS ( cross-eyes) Eye muscles do not coordinate their actions Usually in children Rx – eye exercises or surgery Opthalmoscope = used to examine the eye

Disorders of the Ear Loud noise 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 Conductive hearing loss….may be from excessive wax in ear canal

Disorders of the Ear 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. Sxs – fever, pain, fluid drainage

Other Sensory Problems Phantom Pain After an amputation your brain still sends signals to amputated limb. Neural pathways are still intact. Rhinorrhea Allergies cause constant, clear drainage from nose and down pharynx from maxillary sinuses. May cause chronic pharyngitis.

Other Sensory Problems Thrush (oral yeast infection characterized by white patches on tongue and cheeks) Antibiotics wipe out normal flora which allow fungi to flourish…vaginal and oral yeast infections are common with antibiotic use