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Cochlear Implant 1Anatomy and Physiology

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Auditory system

Auditory system - Wikipedia

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Auditory System

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AN CNIC

MGB

Auditory cortex

Outer Ear

- Pinna

- Ear canal

Middle Ear

- Tympanic

membrane

- Ossicles

Inner Ear

- Cochlea

Cochlea

Ossicles

Oval window

Round

window

Tymapanic

membrane

Auditory

canal

Pinna

SGC=Spiral Ganglion Cells

AN= Auditory Nerve

CN = Cochlear Nucleus (Auditory

Brainstem)

IC = Inferior Colliculus (Auditory Midbrain)

MGB = Medial Geniculate Body (Thalamus)

SGC

main nuclei and fiber tracts of the classical ascending auditory system pathways

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Auditory System Pathways and Prostheses

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AN CN ICMGB

Auditory cortex

Medial

geniculate

nucleus

Inferior

colliculus

Auditory

midbrain Implant

Cochlear

nucleus= Auditory

brainstem Implant

AN= Auditory Nerve

CN = Cochlear Nucleus (Auditory Brainstem)

IC = Inferior Colliculus (Auditory Midbrain)

MGB = Medial Geniculate Body (Thalamus)

SGC

Auditory Cortex

Cochlear Implant

CI: cochlear implant

ABI: auditory brainstem implant

AMI: auditory midbrain implant

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Multiple devices available for hearing problems

5Some modification - F. G. Zeng (Trends Amplif,, 2004)

Hearing Aid:Middle Ear ImplantCochlear ImplantAuditory Brainstem ImplantAuditory Midbrain Implant

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The cochlea

• Cochlea is the first system to perform auditory

processing of the incoming acoustic signal

(sound)

• It will extract frequency, intensity (and other

timing cues) of that signal and transmit those to

the higher auditory pathway

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AN CN IC

Auditory cortexSGC

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Inner Ear: Cochlea

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Scala

Media (SM)

Scala

Tympani (ST)

Auditory

nerve fiber

meaning : snail shell

Spiralled hollow boneAbout 2 and 3/4 turnsAbout 30 mm long

Axis: Modiolus

Cochlea.png: The original uploader was Dicklyon at English Wikipedia derivative work: Fred the Oyster - Cochlea.png

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Cochlea

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Scala

Media (SM)

Scala

Tympani (ST)

Auditory

nerve fiber

Three chambers (scalae)- Scala Vestibuli- Scala Media - Scala Tympani

Filled with incompressible liquids-Perilymph(s.t.and s.v.)-endolymph(s.m.)

Organ of Corti in s.m.

Hair Cells

Basilar membrane

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• widest (0.42–0.65 mm) and least stiff at the apex of the cochlea, and narrowest (0.08–0.16 mm) and most stiff at the base

Oghalai JS. The cochlear amplifier: augmentation of the traveling wave within the inner ear. Current Opinion in Otolaryngology & Head & Neck Surgery. 12(5):431-8, 2004

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Basilar Membrane

Base

(narrow, thick, stiff)

Apex

(wide, thin, floppy)

mm

0 5 10 15 20 22

Base Apex

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Basilar Membrane as a good frequency analyzer

The cochlear operation of frequency analysis is dependent on the

following mechanical properties of the BM

• Graded width

a. The width of the BM increases from base to apex

b Wider or more mass results in lower resonant frequency

• Graded stiffness

a. The stiffness of the BM decreases from base to apex

b. Stiffness results in higher resonant frequency

• Graded mass

a. The BM increases in mass from the base to apex

b. Greater mass results in lower resonant frequency

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Two features are represented in the Basilar Membrane

• Frequency - location of maximum displacement of the BM• Intensity - The amount of deflection of the BM

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Von Bekesy’s Place Theory

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The Place theory by George von Bekesy

• This pressure difference causes displacement of the basilar membrane (BM)• Compression waves drive the BM downward and rarefaction waves drive it upward• Because the BM's physical characteristics and attachments, it has greater displacement longitudinally than radially (transversely), though there is movement across both planes• The wave always travels from the base to the apex

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Tonotopic arrangement of the BM

Different frequencies produce traveling waves that reach their maximum deflections at different places along the cochlear partition• High-frequency stimuli cause maximal displacement of the BM in the basal region of cochlea• Low-frequency sounds cause maximal displacement of the BM in the apical region of the cochlea

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Base

(narrow, thick, stiff)

Apex

(wide, thin, floppy)

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Hair cells

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Inner Hair Cells 3,500Outer Hair Cells 12,000

Spiral ganglion

Cochlear nerve

Organ of corti.svgL Madhero88

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Hair cells

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By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 928, Public Domain, https://commons.wikimedia.org/w/index.php?curid=566872

Organ of corti.svgL Madhero88

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Hearing Loss

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The range of human hearing

• Sound frequency

-over 20-20000Hz

• Sound intensity expressed in

Sound Pressure Level (SPL) in dB

SPL = 20 x log10 (Px / Pref)

where Pref = 2.5 x 10-5 N/m2 ( is the

approximate threshold of human

hearing at 1KHz)

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http://en.wikipedia.org/wiki/Image:Lindos1.svg

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Degree of

Hearing Loss

Hearing Loss Range

(dB SPL)

Normal 10 - 15

Slight 16 - 25

Mild 26 - 40

Moderate 41 - 55

Moderately Severe 56 - 70

Severe 71 - 90

Profound to total 91 and above

Various sound levels (dB SPL)

Quiet Nature <20

Library 35 Living Room 40

Conversation Speech, quite office 60

Average Street noise, average TV audio 70

Night Club Dance Floor 100

Close in Thunder, Loud Rock Concert 120

Gun Shot 150

Degree of Hearing Loss

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Conductive Hearing Loss

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• Middle ear damage

• Conductive Hearing loss is

overcome by

– Hearing Aid (HA)

– Bone Anchored Hearing Aid (BAHA)

– Middle Ear Implant using Floating

Mass Transducer

AN CN LLIC

MGB

Auditory cortex

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Sensorineural Hearing Loss

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Sensorineural hearing loss

: 'Hair cell' or 'auditory nerve' damage in inner near

Overcome by 'cochlear implant'

AN CN LLIC

MGB

Auditory cortex

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Congenital sensorineural hearing loss

• Two types of sensorineural hearing loss:

• Congenital and Acquired sensorineural hearing loss.

• Congenital sensorineural hearing loss happens during pregnancy. Some causes include:– Prematurity

– Maternal diabetes

– Lack of oxygen during birth

– Genetics

– Diseases passed from the mother to the child in the womb, such as rubella.

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Acquired sensorineural hearing loss

Causes include:

• Aging:

• Noise: approximately 15 percent between the ages of 20 and 69 suffer from noise-induced hearing loss (NIHL). Exposure to a one-time loud noise, such as an explosion, or to sounds louder than 85 decibels over an extended period of time.

• Disease and infections: Meniere’s disease, Viral infections, such as measles, meningitis

• Head or acoustic trauma: Damage to your inner ear can also be caused by a blow to the head Tumors

• Medications: more than 200 medications and chemicals are ototoxic

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IHCs

OHCs

Normal hair cells

Normal Haircells

24Auditory cortex

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Impaired Hearing Due to Damaged Haircells

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Deafened (Damaged Hair cells)

Auditory cortex

IHCs

OHCs

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Normal vs. Damaged Hair cells

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Normal Haircell SD rat 14 week old immunofluorecence _apical turn

Damaged Haircell SD rat 14 week old immunofluorecence _middle turn

Courtesy of SNUH ENT SH OH Lab. DH Kim 2016 10

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Restored Hearing by Cochlear Implantation

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Cochlear Electrode Array

Auditory cortex

• Electrode placed in scala tympany

• Target cell is spiral ganglion in modiolus

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CI: the success story

1. Spatially isolated space was available for the electrode array. The electrode array was still electrically connected to the target neurons.

2. Timely development of the transistor based microelectronics technologies that made the electronics small (wearable, implantable) but powerful.

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File:Blausen 0244 CochlearImplant 01.png

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Reference

• Bear, Mark F., Barry W. Connors, and Michael A. Paradiso, eds. Neuroscience. Vol. 2. Lippincott Williams & Wilkins, 2007.

• F.-G.Zeng et al., Brain Research, 2000

• R.B.Stein et al., Nature Review Neuroscience, 2005

• Kandel, Eric R., James H. Schwartz, and Thomas M. Jessell, eds. Principles of neural science. Vol. 4. New York: McGraw-Hill, 2000.L.M.Friesen et al., J. Acoust. Soc. Am, 2001

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