Dynamic Equilibrium Dynamic equilibrium is controlled by the sensory hairs within the ampulla of the semicircular canals – Within each ampulla is a small elevation called the crista

Dynamic Equilibrium Each crista contains hair cells and supporting cells covered by gelatinous material called the cupula – With movement, the endolymph within the ampulla lags behind the moving cupola, causing a difference in the inertial forces – the hair bundle of the cupola bends and nerve impulses are generated

Equilibrium Pathway Once generated, nerve impulse travel up the vestibular branch of CN VIII. Most of these axons synapse in the major integrating centers for equilibrium, in the medulla and pons, which also receive input from the eyes and proprioceptors – Ascending neurons continue  primary auditory area in the parietal lobe to provide us with conscious awareness of the position and movements of the head and limbs

Homeostatic Imbalances A cataract is an opaque defect in the cornea or lens of the eye – most cataracts are in the lens – Cataracts are causes by injury, medications, and diseases like diabetes. They are common in old age Conjunctivitis is an inflammation of the conjunctival membrane which covers part of the front of the eye – Conjunctivitis is caused most frequently by viral infections (pink eye) and allergy. It can also result from bacterial infections and many other irritants

Homeostatic Imbalances Age Related Macular Degeneration results in a loss of vision in the center of the visual field (the macula) because of damage to the retina. It is a major cause of visual impairment in older adults (>50 years) – It can become impossible to recognize faces, yet enough peripheral vision remains to allow other activities of daily life

Homeostatic Imbalances Myringitis is an inflammation of the ear drum – Infections of the middle ear cavity (otitis media) are common in children between 6 mo. – 5 yrs. old, and usually presents with a crying child and a TM (viewed through an otoscope), that looks angry, red, and bulging Otitis externa (commonly called “swimmer’s ear”) is a dermatitis of the epithelium of the outer ear (infectious and noninfectious). The chlorine, water, and ear plugs associated with swimming can result in irritated, inflamed tissues of the outer ear and ear canal

Distended Eardrum Caused by Otitis Media Dr. P. Marazzi/Photo Researchers, Inc.

Homeostatic Imbalances Meniere’s disease is a disorder of the inner ear that can affect hearing and balance, and is thought to be due to increased pressure in the cochlea and semicircular canals (extra endolymph) – Episodes of vertigo (the room spinning) and ringing in the ears (tinnitus) can be a mild annoyance, or a chronic, disabling disability

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