The Reason Ears Were Invented

1. The Reason Ears Were Invented • The original function in evolution? ….Equilibrium, coordination and balance. • The VESTIBULAR APPARATUS : This is where we find Equilibrium Receptors. • Like the hearing “apparatus” in the cochlea the VA has HAIRS too. The hairs work a little differently but the result is the same we get TRANSDUCTION: this time we will transduce motion into nerve impulses.

3. Equilibrium • Control of coordination and balance • Receptors in vestibular apparatus • semicircular ducts contain crista • saccule and utricle contain macula • Gravitational equilibrium – perceived by macula • perception of head orientation • Dynamic or ROTATIONAL equilibrium • perception of motion or acceleration • linear acceleration perceived by macula • angular acceleration perceived by crista

4. We Have 2 Types of Equilibrium: GRAVITIONAL and ROTATIONAL • GRAVITATIONAL; Mechanoreceptors in utricle and saccule detect movement of the head in vertical and horizontal planes. • ROTATIONAL: Mechanoreceptors in semicircular canals detect rotational /angular moment of head.

5. For Our Gravitational Equilibrium • Each MACULA has set of HAIRS embedded in otolithic membrane, a gel-like material has earstones called OTOLITHS • OTOLITHS are calcium salts that rolls in response to change in GRAVITY.

6. Hair cells project into membranous labyrinth Membrane contains otoliths (calcium carbonate) hair cells move against it Utricle more sensitive to horizontal movement, saccule to vertical Semicircular canals arranged at right angles to each other Each has an ampulla in which hair cells are located hair cells move against endolymph

7. Utricle and saccule utricle- head movement away from vertical horizontal movement saccule- head away from horizontal vertical acceleration Semicircular canals- rotational acceleration (maintain balance while turning) Receptors for equilibrium- “hair cells” (modified epithelium) Cell membranes are depolarized when bent, release transmitters

9. Saccule and Utricle • Contain macula • hair cells with stereocilia and onekinocilium buried in a gelatinous otolithic membrane • otoliths add to the density and inertia and enhance the sense of gravity and motion

10. Where are the Saccule and Utricle?

11. What are Otoliths? • Otoliths are like stones, they have weight or rather DENSITY. • Then intensify inertia

12. What Do We Mean By Inertia? • Inertia is Isacc Newton’s First Law of Motion . • It means basically, that a body in its given state of motion tends to stay that way unless stopped by force. • For example: A body at rest will stay at rest unless acted upon by a force OR a body in motion will stay in motion unless acted upon by a force.

13. Macula • Static equilibrium - when head is tilted, weight of membrane bends the stereocilia • Dynamic equilibrium – in car, linear acceleration detected as otoliths lag behind

15. Another part of the ear, the semicircular canals AND another receptor region called: the CRISTA AMPULLARIS The Crista ampullaris consists of a gelatinus cap called the cupula ROTATIONAL Equilibrium

17. Crista Ampullaris - Head Rotation • As head turns, endolymph lags behind, pushes cupula, stimulates hair cells

18. What is MOTION SICKNESS? • When the hair cells send messages that are incongruent with what the eyes are seeing and our body is feeling, as may occur in a boat or aircraft during rough weather, motion sickness can result. • IT is UNKNOWN why some people suffer motion sickness while others are immune to it.

19. Vestibular Projection Pathways

20. Equilibrium Projection Pathways • Hair cells of macula sacculi, macula utriculi and semicircular ducts synapse on vestibular nerve • Fibers end in vestibular nucleus in pons and medulla

21. Equilibrium Projection Pathways • Information sent to 5 targets • cerebellar control of head and eye movements and posture • nuclei of CN III, IV, and VI to produce vestibulo ocular reflex • reticular formation control of blood circulation and posture • vestibulospinal tracts innervate antigravity muscles • thalamic relay to cerebral cortex for awareness of position and movement

22. Diseases of the Ear

23. Conduction Deafness • Any condition that interferes with the transmission of vibrations to the inner ear. Normally, during this type of damage the ossicles FUSE together…can’t move. • Can be caused by congenital defect such as German Measles. • Otosclerosis-normal bone is replaced by spongy bone

24. Sensorineural Deafness • Receptors of the ear are worn away( steriocilia on hairs damaged) • Occurs with normal aging BUT also in younger people exposed to high decibels. (any level above 80 decibels will damage the organ of corti) Some antibiotics make ears more susceptible to damage ( OTOTOXIC) streptomycin, kanamycin, gentomycin

25. Meneire’s Disease • Symptoms: nausea and VERTIGO leading to progressive deafness • Cause not fully known but suspected is arteriolsclerosis, degeneration of cranial nerve VIII and increased pressure of the inner ear fluids. • This is a very uncomfortable disease as patients often cannot stand up without extreme discomfort.

26. Otitis Media • Middle Ear Infection- When upper respiratory infections spread to the Eustacean tube. • Can be serious as, ear infections can spread to brain ( mastoid cells) and lead to meningitis. • Also, recurring ear infections can leading to fusion of the ossicles and hearing loss! • Myringotomy- sometimes used here.