Ear, Hearing and Equilibrium Exercise 27 BI 232 Introduction Functions: Hearing and Equilibrium Mechanoreception: because the ear
receives mechanical vibrations and translates them into nerve impulses Static equilibrium: able to determine nonmoving position Dynamic equilibrium: motion is detected Hearing Vestibular Portion Cochlear Portion
7 Inner Ear 8 Composed of three areas: Cochlea Vestibule Semicircular Ducts
(canals) Labyrinth Cochlea- snail shaped Contains sensory receptors for hearing, known as the organ of Corti (spiral organ) Sensory hair cells are found in all receptor organs of the inner ear which contain long microvilli, called stereocilia
9 These can be stimulated by gravitational forces in the vestibule, turning movements in the semicircular canals or sound waves The stapes strikes the oval window of the cochlea
10 Cochlea Uncoiled oval windo w round windo w vestibular duct Cochlear duct containing the
Organ of Corti helicotrema tympanic duct Stapes pushes on fluid of vestibular duct at oval window At helicotrema, vibration moves into tympanic 11 duct Cochlea 12
Vestibulocochl ear nerve sends impulses to the auditory cortex of the temporal lobe of brain and interpreted as sound Organ of Corti 13
Vestibule Consists of the utricle and saccule Involved in the interpretation of static equilibrium and linear acceleration Regions known as maculae, which consist of hair cells with
stereocilia and a kinocilium grouped together in a gelatinous mass called otolithic membrane and weighted with calcium caronate stones called otoliths Vestibule As the head is
accelerated or tipped by gravity, the otoliths cause the cilia to bend, indicating that the position of the head has changed. Visual cues play a part in this also When visual and vestibular cues are not synchronized, a sense of imbalance or nausea can occur Inner Ear
Semicircular canals contain sensory receptors called crista and detect change in acceleration or deceleration. Dynamic equilibrium 3 semicircular ducts, each at 90 degrees to one another
Filled with endolymph and has an expanded base called an ampulla 16 Ampulla of the semicircular canals Inside are clusters of hair cells and supports cells (crista ampullaris) These cells have
stereocilia and a kinocilium enclosed in a gelatinous material called the cupula. As the head is rotated, the endolymph pushes pushes against the stereocilia. Types of Hearing Loss Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear
canal to the eardrum and the bones of the middle ear. Sensorineural hearing loss occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear to the brain. 18 Weber Test Ring tuning fork and place on center of head. Ask the subject where they hear the sound. Interpreting the test: Normally, the sound is heard in the center of the head or equally in both ears.
Sound localizes toward the poor ear with a conductive loss Sound localizes toward the good ear with a sensorineural hearing loss 19 Rinne Test Place the vibrating tuning fork on the base of the mastoid bone. Ask patient to tell you when the sound is no longer heard. Immediately move the tuning fork to the front of the ear
Ask the patient to tell you when the sound is no longer heard. Repeat the process putting the tuning fork in front of the ear first 20 Rinne Test Normally, someone will hear the vibration in the air (in front of the ear) after they stop
hearing it on the bone Conductive hearing loss: If the person hears the vibration on the bone after they no longer hear it in the air. 21 Bing Test
Similar to the Rinne Test Strike the tuning fork and place it on the mastoid process. With your other hand close off the auditory canal with pad of finger. A person with normal hearing or one with sensorineurial hearing loss will hear the sound better when ear canal is closed. A person with conductive hearing loss will not
notice a change in sound Sound Location Have lab partner sit with eyes closed. Strike the tuning fork with a rubber reflex hammer above head. Have partner describe
to you where the sound is located. Try the following locations: behind head, right side, left side, in front of head, below chin Postural Reflex Test
Unexpected changes that move the body away from a state of equilibrium cause postural reflexes to compensate for that change. Important for maintaining the upright position of the body. Negative feedback mechanisms Find an area w/o obstacles Stand on tiptoes and read lab manual Lab partner should give a little nudge to left or right (not too hard) Baranys Test
Tests visual responses to changes in dynamic equilibrium. Place subject in a swivel chair with four or five students close by. Subject sits in chair and tilts head forward about
30 degrees Spin the chair about 10 times Notice twitching of the eyes (nystagmus) after stopping. Romberg Test
Tests static equilibrium Subject stands with back to the wall. Dont lean on wall Stand for 1 minute and have partner watch for swaying Do the same exercise again but have subject close eyes The End
Identify structures on models View and identify structures on cochlea slides Make sure that you understand the tests What cranial nerve is being innervated with the tests performed in lab?
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