THE EAR
Sound waves--- > outer ear -----> special
receptor cells-->
Nerve fibers----->
auditory region of brain (sound)
Regions
of the ear:
·
Outer (external) ear
·
Pinna/auricle (outer flap)
·
External auditory meatus/canal - carries sound waves
·
Middle ear
·
Inner ear
Middle ear figure
Tympanic membrane
(eardrum)
sound
waves pass through auditory canal
vibrations
move ossicles (bones) that conduct waves through middle ear:
§
malleus (hammer)
§
incus (anvil)
§
stapes (stirrup)
Eustachian (auditory)
tube - canal leading from middle ear to pharynx
Inner ear
(labyrinth)
·
Circular, maze-like structure
·
Oval window - separates middle and inner ear
·
Cochlea - snail shaped
·
Contains fluid through which sound waves travel
·
Organ of corti - auditory receptor area relaying sound to auditory
nerves: contains structures that help maintain equilibrium
The
ear: abnormal and pathological conditions
Meniere's disease - disorder of the inner ear(labyrinth) due to
elevated endolymph pressure in the cochlea.
·
Symptoms: tinnitus, progressive loss of hearing, cephalgia,
nausea,vertigo.
Otosclerosis - ankylosis
(hardening) of the bony tissue in the labyrinth (inner ear); bony tissue forms
around the oval window and can fuse with the stapes preventing passage of sound
vibrations.
·
Treatment: stapedectomy with tissue graft and wire.
Serous otitis media - noninfectious
inflammation of the middle ear with accumulation of serum (fluid).
·
Treatment: myringotomy and aspiration plus tympanostomy tubes.
Suppurative otitis
media
- bacterial infection of middle ear with pus formation.
·
Treatment: antibiotics,
myringotomy.
Tinnitus (tinkling) - noise in
the ear caused by presbycusis, Meniere's disease, otosclerosis, chronic otitis,
etc.
Vertigo - irregular or
whirling sensation of self or external objects resulting from disease in
labyrinth or nerve carrying messages to the brain. Affects equilibrium and balance, possible nausea.
Clinical procedures
Audiometry - use of an instrument (audiometer) to determine ability to hear at
different frequencies. Results are
plotted on an audiogram.
Otoscopy - use of an otoscope
to visually examine the ear.
THE EYE
Receptors receive stimuli à nerve à impulses à brain à through afferent sensory neurons, which produces sensations of light (vision).
Pupil – light enters eye.
Conjunctiva – mucus membrane lining eyelids and covers interior portion of the eye.
Cornea – bends (refracts) light rays.
Sclera – tough, white outer cover of eyeball.
Choroid – vascular layer between sclera and retina.
Iris – colored part of eye; has muscles to dilate or constrict pupil.
Ciliary body
Optic disk – blind spot at back of eye where optic nerve meets the retina.
Fovea centralis – region of clearest vision; located within macula lutea.
Macula lutea – yellowish area of retina near the optic disk.
Crystalline lens – transparent body behind the pupil which bends light rays (refraction).
Distant object – lens is flattened; rays slightly bent.
Near object – lens becomes thicker; rays bend more.
Vitreous chamber – area behind the lens containing vitreous humor (not constantly reformed).
Retina – light-sensitive nerve cell layer (inner layer).
Optic nerve – cranial nerve carrying impulses from retina to brain.
Optic chiasma (crossing) – point where medial fibers of optic nerve cross in the brain. All fibers from right half of each retina form an optic track. Left fibers do the same.
All fibers from right half of each retina form an optic track. Left fibers do the same.
Binocular vision – left and right images are fused, resulting in single, 3-dimensional vision.
Presbyopia – visual impairment due to old age. Ciliary body is less elastic, impairing vision.
THE EYE: PATHOLOGICAL CONDITIONS
Cataract – clouding of the lens, resulting in decreased vision.
Diabetic retinopathy – hemorrhages, etc. in the retina, leading to edema, scarring and blurred vision.
Glaucoma – increased intraocular pressure due to:
Macular degeneration – degeneration of yellowish region at back of retina causes severe loss of central vision. Peripheral vision is retained.
Retinal detachment – separation of layers due to eye trauma, head injuries, bleeding, scarring from infection, shrinkage of vitreous humor. Patients may see flashes of light.
Ophthalmoscopy – visual exam of the interior of the eye.
Fluorescein angiography – fluorescein dye injected IV to detect movement of blood … diabetic or hypertensive retinopathy, lesions in macular area.
Tonometry – measure pressure within eye … glaucoma.
Cataract surgery – removal of all or part of lens; generally with an intraocular lens implant.
· Aspiration-irrigation – withdraw lens material with a hollow needle.
· Phacoemulsification – use of ultrasound to break up lens; particles are aspirated.
Keratoplasty – also called corneal transplant. Replacement of cloudy (opaque) cornea with normal transplant cornea.
Laser photocoagulation – use of lasers (high energy light) to coagulate blood vessels within the eye. Useful for diabetic retinopathy and age-related macular degeneration.