ear: hearing and equilibrium nestor t. hilvano, m.d., m.p.h
TRANSCRIPT
Ear: Hearing and Equilibrium
Nestor T. Hilvano, M.D., M.P.H.
Learning Objectives
1. Describe the structures and functions of the external, middle, and internal ear.
2. Describe the receptors for vestibular sense (equilibrium) and explain how they function.
3. Trace the vestibular pathway.4. Describe the cochlear duct and the receptor for
hearing.5. Discuss the reception and transduction of sound
energy or hearing process.6. Trace the auditory pathway.7. Explain common clinical conditions associated with
vestibular and auditory problems.
Anatomy of Ear• External Ear:
- collect/detect sound waves____- fleshy and cartilagenous____ passageway____ thin, semitransparent sheet
• Middle Ear:- transmit sound to inner ear. ____- communicates the middle ear with nasopharynx. ____- 3 small bones, conduct vibrations of sounds;
tensor tympani (VCN) – stiffens t.m.; stapedius (VIICN reduces movement of stapes at oval window
a. external auditory canal b. pinna (auricle) c. tympanic membraned. auditory (eustachian) tube e. ossicles
Anatomy of Ear
• Inner Ear – receptors for equilibrium and hearing• Bony labyrinth surrounds membranous labyrinth • Bony labyrinth subdivided into:
a) Vestibule – encloses saccule and utricleb) Semicircular canals – contain semicircular ductsc) Cochlea – contains cochlear duct
• Round window – separates perilymph from air spaces of middle ear
• Oval window – connected to base of stapes
Equilibrium • Maculae - receptors which perceived the
sense of gravity and acceleration;when head is tilted, weight of membrane bends the stereocilia
• Cristae ampullaris- receptor for sense of rotation; orientation causes ducts to be stimulated
Vestibular Projection Pathways• Vestibular receptor to sensory neuron and axons
form the vestibular nerve• Nerve synapse to vestibular nuclei within pons & medulla• Information sent to targets:
____- unconscious control of head and posture
____- to nuclei of CN III, IV, VI
____- innervate antigravity muscles (peripheral m. tone)
____- conscious sense of head position and movementa.vestibulo-cerebral tracts b. vestibulospinal tracts
c.Vestibulo-ocular tracts d. vestibulo-cerebellar tracts
* Nystagmus – due to damage of BS or inner ear
Cochlear Duct – Organ of Hearing • Scala media (cochlear duct) separated from
scala vestibuli by vestibular membrane, and from scala tympani by basilar membrane.
• Spiral organ of corti contains receptor cells called ___.a. bipolar cells b. hair cells
c. dendritic cells d. sustentacular
• Frequency (pitch) of sound - determined by which part of cochlear duct is stimulated.
• Intensity (loudness) - determined by number of hair cells stimulated.
• Physiology of hearing- trace the passage of sound from the external ear to the internal ear
Auditory Pathway• Hair cells of organ of corti• axons form cochlear (VIII) nerve • synapse in cochlear nuclei• ascends to the inferior colliculi of the
midbrain – process fluctuations in pitch during speech– produce startle response; head turning to loud
sound• auditory information synapse in the Medial
Geniculate Bodies of the thalamus• and projected to primary auditory cortex
(Heschl gyri) of temporal lobe.
Nature of Sound• Pitch – frequency vibrates specific parts
of ear
- hearing range is 20 (low pitch) - 20,000 Hz (cycles/sec)- speech is 1500-4000 where hearing is most
sensitive
• Loudness – amplitude; intensity of sound energy (decibels)
• Audiometry test – differentiate high and low frequency sound.
Clinical correlation • Aging – tympanic membrane less flexible, ossicles
stiffens, and round window ossify. • Types of Deafness:
a. Conduction deafness – Rhine’s test BC better than AC; Weber’s test sound appear louder in abnormal ear) b. Sensorineural (Neural) deafness – Rhine’s test both are decrease, but AC remain better than BC; Weber’s test sound appear louder in normal ear)
• Vertigo – damage to vestibular receptor• Nystagmus, gait problems – seen in lesion of
vestibular nucleiIdentify type of deafness in:____ atrophy of cochlear nerve; ____ otitis media____ impacted cerumen; ____ hereditary deafness
Homework (Self-Review) 1. Give the function/s of the following: a) cerumen, b)
auricle, c) macula, d) crista ampullaris, e) basilar membrane, f) tectorial membrane, g) spiral ganglion, h) organ of corti, i) tympanic membrane.
2. What is auditory (eustachian) tube? Discuss the occurrence of ear pain when it is blocked.
3. Identify the subdivisions of bony labyrinth and membranous labyrinth.
4. Trace the auditory pathway from the receptor to brain.5. Type of deafness in: a) otitis media, torn tympanic
membrane, and impacted cerumen, and b) atrophy of cochlear nerve and damage of organ of corti.
6. What fluid is contained in scala media? In scala vestibuli and scala tympani?
7. Study anatomy illustration of ear and it’s parts (refer to text reference).