Sensory System – Notes Outline
Sensory System – Notes Outline
Sensory System
1H12.01 Explain the structure of the eye.
A. Eye
1. 1” in diameter
2. Protected by orbital cavity, eyebrows, eyelashes, eyelids
3. Lacrimal glands – tears empty into nasal cavity
4. Conjunctiva – thin membrane lines eyelids
5. Wall of eye made up of three coats
B. Sclera
1. Outer layer
2. White of the eye
3. Tough coating, helps maintain shape of eye
4. Muscles responsible for moving eye attached to sclera = extrinsic muscles
C. Cornea
1. Front of sclera (clear part) no blood vessels
2. Transparent so light rays can pass through
D. Choroid coat
1. Middle layer, contains blood vessels
2. Opening in front is pupil
3. Colored, muscular layer surrounding pupil is iris
4. Intrinsic muscles – change size of iris to control amount of light entering through pupil
E. Lens
1. Crystalline structure located behind iris and pupil
2. Elastic, disc-shaped, biconvex
3. Situated between the anterior and posterior chambers
F. Anterior Chamber – filled with aqueous humor
G. Posterior Chamber – filled with vitreous humor
H. Retina
1. Innermost layer
2. Light rays focus image on retina
3. Image travels to the cerebral cortex via optic nerve
4. Rods – sensitive to dim light
5. Cones – sensitive to bright light and color
6. Optic disc – on retina, known as blind spot, nerve fibers that form optic nerve
1H12.02 Analyze the function of the eye.
A. Eye
1. Protected by orbit, eyebrows, eyelashes, eyelids
2. Lacrimal glands – tears empty into nasal cavity and clean the eyes
3. Conjunctiva – secretes mucous to lubricate eyes
B. Sclera
1. Tough coating, helps maintain shape of eye
2. Extrinsic muscles - responsible for moving eye attached to sclera
C. Cornea - Transparent so light rays can pass through
D. Choroid coat
1. Middle layer, contains blood vessels
2. Intrinsic muscles – change size of iris to control amount of light entering through pupil
3. Pupil constricts – gets smaller – in bright light
4. Pupil dilates – gets larger – in dark light
E. Lens
1. Where light rays are refracted
2. Accommodation – change in the shape of the lens to allow for near and distant vision
F. Retina
1. Light rays focus image on retina
2. Image travels to the cerebral cortex via optic nerve
3. Rods – sensitive to dim light
4. Cones – sensitive to bright light and color
5. Optic disc – on retina, known as blind spot, nerve fibers that form optic nerve
G. Pathway of vision - Image travels through cornea, then pupil, through lens, hits retina, picked up by rods and cones and carried to optic nerve where the brain interprets image
1H12.03 Explain the structure and function of the ear, nose, and tongue.
A. Outer ear
1. Pinna (auricle)
a. Visible ear
b. Collects sound waves
2. External auditory canal – ear canal
3. Cerumen – ear wax, protects the ear
4. Tympanic membrane – ear drum, separates outer and middle ear
B. Middle ear
1. Cavity in temporal bone
2. Connects with pharynx by Eustachian tube - which equalizes pressure in the middle ear with outside atmosphere
3. Bones - transmit sound waves from ear drum to inner ear
a. Malleus (hammer)
b. Incus (anvil)
c. Stapes (stirrup)
C. Inner ear
1. Cochlea - spiral shaped organ of hearing, contains a membranous tube, the cochlear duct – which is filled with fluid that vibrates when sound waves are transmitted by the stapes
2. 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
3. Semicircular canals – three structures in inner ear that contain liquid set in motion by head and body movements
4. Impulses sent to cerebellum to help maintain body balance (equilibrium)
D. Pathway of hearing – ear to external auditory canal to tympanic membrane to ossicles (malleus, incus and stapes) to cochlea to auditory nerve to brain
E. Nose
1. Smell accounts for 90% of taste
2. Tissue in the nose, olfactory epithelium, contains specialized nerve cell receptors
3. Those receptors stimulate the olfactory nerve to the brain
F. Tongue
1. Mass of muscle tissue
2. Bumps on surface are papillae, they contain taste buds
3. Receptors in taste buds send stimuli through 3 cranial nerves to cerebral cortex
1H12.04 Discuss characteristics and treatment of common sensory disorders.
A. Disorders of the eye
1. Conjunctivitis (Pink eye)
a. Inflammation of conjunctival membranes in front of eye
b. Redness, pain, swelling and discharge
c. Highly contagious
d. Rx – antibiotic eye drops
2. Glaucoma
a. Excessive intraocular pressure causing destruction of the retina and atrophy of the optic nerve
b. Caused by the overproduction of aqueous humor, lack of drainage, or aging
c. Symps – develop gradually, mild aching, loss of peripheral vision, halo around light
d. Tonometer – measures intraocular pressure
e. Rx – drugs or laser surgery
3. Cataracts
a. Lens of eye gradually becomes cloudy
b. Frequently occurs in people over 70
c. Causes painful, gradual blurring and loss of vision
d. Rx – surgical removal of the lens
4. Sty (hordeolum)
a. Abscess at the base of an eyelash in sebaceous gland
b, Symps – red, painful, swollen
c. Rx – warm, wet compresses
5. Eye injury - Glass or fragment in eye – cover eye and seek medical help, do not remove the object
6. Color blindness
a. Cones affected
b. Genetic disorder that is carried by female and transmitted to males
B. Vision defects
1. Presbyopia
a. Lens loses elasticity, can’t focus on close or distant objects
b. Usually after age 40
c. Rx – bifocals
2. Hyperopia
a. Farsighted
b. Focal point beyond retina, eyeball too short
c. Convex lenses help
3. Myopia
a. Nearsighted
b. Eyeball too long
c. Concave lenses help
4. Astigmatism
a.. Irregular curvature of the cornea or lens, causing blurred vision or eye strain
b. Rx – corrective lenses
5. Diplopia – double vision
6. Strabismus (cross-eyed)
a. Eye muscles to not coordinate their actions
b. Usually in children
c. Rx – eye exercises or surgery
7. Ophthalmoscope – instrument for viewing inside the eye
8. Snellen eye chart – chart that uses letters or symbols in calibrated heights to check for vision defects
C. Disorders of the ear
1. Hearing loss
a. Hearing is fragile, loud noise over period of time can cause hearing loss
b. Symps – tinnitus (ringing in ears) and difficulty understanding what people are saying
2. Otitis Media
a. Infection of middle ear
b. Often complication of common cold in children
c. Rx – antibiotics
d. Myringotomy – tubes inserted through tympanic membrane to relieve pressure
3. Otosclerosis
a. Chronic , progressive middle ear disorder
b. Stapes becomes spongy and then hardens, becoming fixed and immobile
c. Rx – stapedectomy and total replacement of stapes
4. Tinnitus – ringing of ears from impacted wax, otitis media, loud noise, etc.
5. Types of hearing loss
a. Conductive – sounds prevented from reaching inner ear
b. Sensorineural – problem with inner ear and auditory nerve
D. Disorders of the nose
1. Rhinitis
a. Inflammation of lining of nose with congestion, drainage
b. Cause – allergies, drugs, infection, odors, etc.
c. Rx – eliminate cause, antihistamine
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