Inner Ear Balance Mechanisms Balance Mechanisms Vestibule Semicircular

Inner Ear Balance Mechanisms

Balance Mechanisms • Vestibule • Semicircular Canals

Static Equilibrium

Static Equilibrium • associated with vestibule • receptors in chambers saccule and utricle and contain maculae

Static Equilibrium • Reports on body position in respect to gravity • Responds to linear acceleration

• each maculae is a flat patch of epithelium with scattered supporting cells and 20 -50 receptor “hair” cells

• hair cells are embedded in a jelly-like membrane that also contains tiny Ca crystals called otoliths (ear stones)

• displacement activates receptors because hair cells move

Dynamic Equilibrium

Dynamic Equilibrium • monitored by the ampullae at base of the semicircular canals • evaluates the change in rate of movement

• inside each is a crista ampullaris with hair cells in jelly covering - cupula Semicircular canal cupula ampulla hair cell

• each canal orients in a different place so acceleration at all angles can be monitored

• if constant rotation occurs, hairs will quit bending and bend the other way when we stop • bony labyrinth moves with body - fluid and gels move at various rates depending on different forces

Ear Disorders

Motion Sickness • difficult to explain • probably due to sensory input mismatch caused by continuous stimulation of the semicircular canals • consists of nausea and weakness

Deafness or hearing loss can be: 1. Conduction § Outer ear or middle ear 2. Sensorineural § Inner ear

1. Conduction • something interferes with vibrations or transmission of sound waves

Examples of causes: ear wax build up ruptured eardrum

Examples of causes: otosclerosis connective tissue grows over stapes and oval window

• helped by hearing aid and surgery

2. Sensorineural • Involves damage to the organ of Corti hair cells or nerve pathways

Examples of Causes: • Loud noise that pulls hair cells away from nerve endings

Examples of Causes: Tumors

• Cochlear implants convert sound to electrical stimuli delivered to the cochlear nerve