Equilibrium

1. Equilibrium How the inner ear keeps me upright

3. Static Equilibrium • Based on the position of the head (body) relative to the force of gravity • Takes place in the vestibule of the inner ear • Specifically involves two structures: 1. Saccule, and 2. Utricle

4. How does it work? • Within the utricle and saccule a small thickened region called the Macula is responsible for the information necessary to remain upright • The maculae (2) are perpendicular to each other and they provide the sensory information that gives feedback on the position of the head relative to the surroundings • This information allows us to maintain balance and posture • The macula also detect linear acceleration and deceleration

5. What is the Macula made of? • Two cell types: • 1) Hair Cells---the sensory receptors • 2) Supporting Cells— • The hair cells have a thick gelatinous material that sits on them called the Otolithic membrane and dense calcium carbonate stones called otoliths

8. Equilibrium Function • As we move our head, the gelatinous layer moves with us and bends the hairs • The otoliths also “roll” with us and stimulate the production of action potentials that are interpreted as movement • Can detect front/back/and side to side movement of head • If the eyes detect movement (driving) but we are still, this can lead to motion related sickness

9. Dynamic Equilibrium • This is our moving equilibrium • Not based in vestibule, but rather in the 3 semicircular ducts that lie at right angles to one another in 3 planes of space • Two of the ducts are vertical, and lie in an anterior and posterior position • The other duct is horizontal and faces in a lateral direction • This specific positioning allows us to detect rotational acceleration or deceleration and movement in all directions

11. How does it work? • Each duct has a dilated portion called the ampulla and within this structure a crista is located • The crista have a group of hair cells and supporting cells that are covered by a gelatinous material called the Cupula • When we move, the stimulated canal and hair cells move with us and the endolymph (fluid within the semicircular canal) lags behind • This allows for the hair cells to bend and to generate ap’s that allow us to detect movement

12. What is vertigo? • Inappropriate sensation of movement • Caused by infection, neck injury, strokes, tumors, medications, Meniere’s disease. • Person will experience spinning, tilting, swaying, nausea and inappropriate eye movement • Treatment varies depending on the cause and severity

13. What is deafness? • Any loss of hearing • Two types exist: • 1. Conduction deafness – inner ear is fine, no nerve damage is present but something is not allowing sound to travel to the inner ear for processing • Could be ear wax, pus, foreign object, or old age related • Treatment includes removal of object, hearing aids, medication….etc.

15. What is deafness? • 2. Sensorineural Deafness – damage to the nervous parts of the ear • Can be caused by damage to the cochlea, cochlear nerve, processing centers of brain, or organ of corti • Need to have a cochlear implant to replace the damaged nerve tissue • No hearing aids will work in this case because the ear cannot generate its own action potentials

16. What is deafness? • 3. Meniere’s Disease • Degeneration of cranial nerve #8 • Thought to be caused by a build up of fluid and pressure in the ear • Progressive deafness is an issue because the disease comes and goes in a series of “attacks” • Creates issues with balance and movement as well • Happens in individuals between the ages of 40-60 • Usually starts in one ear but progresses to the other • People who have it complain of ringing, hissing, “static” in ear • No cure exists