Presentation1 - Linn–Benton Community Collegecf.linnbenton.edu/.../Lecture_11_Hearing_and_Equilibrium.pdfPhysiology of hearing Sounds set up vibrations in air that beat against the

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Hearing and

Equilibrium

The Special Senses

• The organ of hearing and equilibrium

– Cranial nerve VIII - Vestibulocochlear

– Regions

• External ear

• Middle ear

• Internal ear (labyrinth)

The Ear

• Two parts

– Pinna or auricle (external structures)

– External auditory meatus (car canal)

• Site of cerumen (earwax) production

– Waterproofing, protection

• Separated from the middle ear by the tympanic membrane

(eardrum)

– Vibrates in response to sound waves

External Ear

Figure 15.25a

External

acoustic

meatus

Auricle

(pinna)

(a) The three regions of the ear

Helix

Lobule

Pharyngotympanic

(auditory) tube

Tympanic

membrane

External

ear

Middle

ear

Internal ear

(labyrinth)

• Tympanic cavity

– Air-filled chamber

– Openings

• Tympanic membrane – covers opening to outer ear

• Round and oval windows – openings to inner ear

• Epitympanic recess – dead-end cavity into temporal bone of unknown

function

• Auditory tube

– AKA Eustachian tube or pharyngotympanic tube

Middle Ear

Figure 15.26

Pharyngotym-

panic tube

Tensor

tympani

muscle

Tympanic

membrane

(medial view)

Stapes

Malleus

View

Superior

Anterior

Lateral

IncusEpitympanic

recess

Stapedius

muscle

Middle Ear

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• Auditory tube (Eustachian tube)

– Connects the middle ear to the nasopharynx

• Equalizes pressure

– Opens during swallowing and yawning

Middle Ear

• Otitis Media

Middle Ear

• Contains auditory ossicles (bones)– Malleus

– Incus

– Stapes

• Middle ear is air-filled; inner ear is fluid-filled

• Sound is mostly reflected from a liquid medium

Middle Ear

• Sound waves cause tympanic membrane to vibrate

• Ossicles help transmit vibrations into the inner ear

– Reduce the area where force is applied

– Increases the pressure of the force enough to transfer most of the

energy into the liquid

– Reflexive muscle action

restricts the movement of

the bones during loud

noises

Middle Ear

• Contains functional organs for hearing & equilibrium

–Bony labyrinth - filled with perilymph

–Membranous labyrinth – functional component

• Filled with endolymph

• Location of various

inner ear receptors

Inner Ear

Figure 15.27

Anterior

Semicircular

ducts in

semicircular

canals

Posterior

Lateral

Cristae ampullares

in the membranous

ampullae

Utricle in

vestibule

Saccule in

vestibule Stapes in

oval window

Temporalbone

Facial nerve

Vestibular

nerve

Superior vestibular ganglion

Inferior vestibular ganglion

Cochlear

nerve

Maculae

Spiral organ

(of Corti)Cochlearductin cochlea

Round

window

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• Labyrinth is modified to form 3 distinct regions

–Vestibule

• Gravity

• Head position

• Linear acceleration and deceleration (changes in speed)

–Semicircular canals

• Angular acceleration and deceleration (changes in direction)

–Cochlea

• Vibration

Inner ear - Labyrinth

* Note: It is always the membranous labyrinth that contains the receptors

Figure 15.27

Anterior

Semicircular

ducts in

semicircular

canals

Posterior

Lateral

Cristae ampullares

in the membranous

ampullae

Utricle in

vestibule

Saccule in

vestibule Stapes in

oval window

Temporal

bone

Facial nerve

Vestibular

nerve

Superior vestibular ganglion

Inferior vestibular ganglion

Cochlear

nerve

Maculae

Spiral organ

(of Corti)Cochlearductin cochlea

Round

window

• The cochlea

– A spiral, conical, bony chamber

– Still 2 portions of bony labyrinth enclosing a portion of membranous

labyrinth

Inner Ear

Figure 15.28a

(a) Helicotrema

Modiolus Cochlear nerve,division of thevestibulocochlearnerve (VIII)

Cochlear duct

(scala media)

Spiral ganglion

Osseous spiral lamina

Vestibular membrane

Bony

labyrinth

Membranous

labyrinth

Bony

labyrinth

• Cavity of the cochlea is divided into 3 chambers

– Vestibular canal (scala vestibuli)

• Vestibular membrane

– Cochlear duct (scala media)

• Basilar membrane supporting Organ of Corti

– Organ of hearing

– Tympanic canal (scala tympani)

Inner ear

Figure 15.28b

(b)

Cochlear duct(scala media;containsendolymph)

Tectorial membrane

Vestibular membrane

Scalavestibuli(containsperilymph)

Scala tympani

(contains

perilymph)Basilar

membrane

Spiral organ

(of Corti)

Stria

vascularis

Spiral

ganglion

Osseous spiral lamina

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Figure 15.28c

(c)

Tectorial membrane Inner hair cell

Outer hair cells

Hairs (stereocilia) Afferent nerve

fibers

Basilar

membrane

Fibers ofcochlearnerve

Supporting cells

Organ of Corti

Organ of Corti

• Transduction of sound

Mechanical energy in middle ear

Fluid pressure wave in inner ear

Nerve impulse

Physiology of hearing

Sounds set up vibrations in air that beat against the eardrum that pushes a chain of tiny bones that press fluid in the internal ear against membranes that set up shearing forces that pull on the tiny hair cells that stimulate nearby neurons that give rise to the impulses that travel to the brain – and you hear.

(This is from your textbook)

Physiology of Hearing in a Nutshell

Figure 15.29

Area of

high pressure

(compressed

molecules)

Crest

Trough

Distance Amplitude

Area of

low pressure

(rarefaction)

A struck tuning fork alternately compresses

and rarefies the air molecules around it,

creating alternate zones of high and

low pressure.

(b) Sound waves

radiate outward

in all directions.

Wavelength

Air

pressure

Figure 15.30

Time (s)

(a) Frequency is perceived as pitch.

High frequency (short wavelength) = high pitch

Low frequency (long wavelength) = low pitch

(b) Amplitude (size or intensity) is perceived as loudness.

High amplitude = loud

Low amplitude = soft

Time (s)

Pre

ssu

re

Pre

ssu

re

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Scala

vestibuli

Cochlear duct

(contains endolymph)

Scala

tympani

Perilymph

Basilar

membrane

Cochlea

Sound waves

HelicotremaStapes vibrating

in oval windowMalleus Incus

External auditory

canal

Tympanic

membrane

Secondary tympanic

membrane vibrating

in round windowAuditory tube

Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ

(organ of Corti)

1

Scala

vestibuli

Cochlear duct


Scala

tympani

Perilymph

Basilar

membrane

Cochlea

Sound waves



External auditory

canal

Tympanic

membrane

Secondary tympanic

membrane vibrating


Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ

(organ of Corti)

1 2

Scala

vestibuli

Cochlear duct


Scala

tympani

Perilymph

Basilar

membrane

Cochlea

Sound waves



External auditory

canal

Tympanic

membrane

Secondary tympanic

membrane vibrating


Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ

(organ of Corti)

1 2

3

Scala

vestibuli

Cochlear duct


Scala

tympani

Perilymph

Basilar

membrane

Cochlea

Sound waves



External auditory

canal

Tympanic

membrane

Secondary tympanic

membrane vibrating


Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ

(organ of Corti)

1 2

3

4Scala

vestibuli

Cochlear duct


Scala

tympani

Perilymph

Basilar

membrane

Cochlea

Sound waves



External auditory

canal

Tympanic

membrane

Secondary tympanic

membrane vibrating


Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ

(organ of Corti)

1 2

3

4

5Scala

vestibuli

Cochlear duct


Scala

tympani

Perilymph

Basilar

membrane

Cochlea

Sound waves



External auditory

canal

Tympanic

membrane

Secondary tympanic

membrane vibrating


Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ

(organ of Corti)

1 2

3

4

5

6

Scala

vestibuli

Cochlear duct


Scala

tympani

Perilymph

Basilar

membrane

Cochlea

Sound waves



External auditory

canal

Tympanic

membrane

Secondary tympanic

membrane vibrating


Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ

(organ of Corti)

1 2

3

4

5

6

7

Scala

vestibuli

Cochlear duct


Scala

tympani

Perilymph

Basilar

membrane

Cochlea

Sound waves



External auditory

canal

Tympanic

membrane

Secondary tympanic

membrane vibrating


Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ

(organ of Corti)

1 2

3

4

5

6

78

8

Scala

vestibuli

Cochlear duct


Scala

tympani

Perilymph

Basilar

membrane

Cochlea

Sound waves



External auditory

canal

Tympanic

membrane

Secondary tympanic

membrane vibrating


Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ

(organ of Corti)

1 2

3

4

5

6

78

8

9

Figure 15.31a

Scala tympani

Cochlear duct

Basilar

membrane

1 Sound waves vibrate

the tympanic membrane.

2 Auditory ossicles vibrate.

Pressure is amplified.

3 Pressure waves created by

the stapes pushing on the oval

window move through fluid in

the scala vestibuli.

Sounds with frequencies

below hearing travel through

the helicotrema and do not

excite hair cells.

Sounds in the hearing range

go through the cochlear duct,

vibrating the basilar membrane

and deflecting hairs on inner

hair cells.

Malleus Incus

Auditory ossicles

Stapes

Oval

window

Scala vestibuli

Helicotrema

Cochlear nerve

32

1

Round

window

Tympanic

membrane

(a) Route of sound waves through the ear

Figure 15.31b

Fibers of basilar membrane

(b) Different sound frequencies cross the

basilar membrane at different locations.

Medium-frequency sounds displace

the basilar membrane near the middle.

Low-frequency sounds displace the

basilar membrane near the apex.

Base

(short,

stiff

fibers)

Frequency (Hz)

Apex

(long,

floppy

fibers)

Basilar membrane

High-frequency sounds displace

the basilar membrane near the base.

Figure 15.28c

(c)

Tectorial membrane Inner hair cell

Outer hair cells

Hairs (stereocilia) Afferent nerve

fibers

Basilar

membrane

Fibers ofcochlearnerve

Supporting cells

•Movement of the basilar membrane bends the hair cells

Figure 15.33

Medial geniculate

nucleus of thalamus

Primary auditory

cortex in temporal lobe

Inferior colliculus

Lateral lemniscus

Superior olivary nucleus

(pons-medulla junction)

Spiral organ (of Corti)

Bipolar cell

Spiral ganglion of cochlear nerve

Vestibulocochlear nerve

Medulla

Midbrain

Cochlear nuclei

Vibrations

Vibrations

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• Timing comparison

– Side nearest sound detects sound first

• Comparison of volume

– High pitched = blocked by head

• Perceived as loudest in ear nearest the source

– Low pitched = curve around head

• Perceived as equally loud in both ears

Localization of Sound

• Conductive deafness– Interference in movement of middle ear bones

• Impacted earwax, perforated eardrum or otosclerosis of the ossicles (overgrowth of bone)

• Sensorineural deafness–Damage to the neural structures

• Aging, prolonged exposure to loud sounds

Abnormalities of hearing

• Otitis media


• Otosclerosis


• Meniere’s Disease

– Episodes of vertigo

– Progressive hearing loss

– Tinnitus

– Feeling of fullness or

pressure in ear

– Usually only in one ear


• Tinnitus

– Ringing, clicking, hissing, or roaring

– Sometimes can be heard with a stethoscope (objective tinnitus)

– May occur in the same rhythm as the heartbeat

– Caused by noise-induced hearing loss, ear infections, diseases of blood

vessels, head injury, neurological problems, brain tumors, earwax…


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• Information about position and movement of head

–Vestibular apparatus

• Utricle

• Saccule

• Semi-circular canals

Physiology of Equilibrium

Vesibule

Figure 15.34

Macula of

saccule

Otoliths

Hair bundle

Kinocilium

Stereocilia

Otolithic

membrane

Vestibular

nerve fibers

Hair cells

Supporting

cells

Macula of

utricle

Vestibular Apparatus

Maculae are

perpendicular

to one another

• Macula = receptor

–Utricle

• Horizontal movements

• Tilting the head side to side

–Saccule

• Vertical movements

Vestibule

– Crista ampullaris

• Sensory receptor for dynamic equilibrium

– One in the ampulla of each semicircular canals

– Major stimuli are rotatory movements

Semi-Circular canals

Figure 15.36a–b

Fibers of vestibular nerve

Hair bundle (kinocilium

plus stereocilia)

Hair cell

Supporting

cell

Membranous

labyrinth

Crista

ampullaris

Crista

ampullaris

Endolymph

Cupula

Cupula

(a) Anatomy of a crista ampullaris in a

semicircular canal

(b) Scanning electron

micrograph of a

crista ampullaris(200x)

• Motion Sickness

– Conflicts between eye movements and equilibrium

• Nystagmus

• Physiologic

– Involuntary eye movement, part of a reflex

– Preserves clear vision during rotation of the head

• Pathologic

– Abnormal eye movement – eyes move as though the head is rotating

while the head is still

– Caused by damage to any part of the vestibular system

Equilibrium

Documents

Presentation1 - Linn–Benton Community Collegecf.linnbenton.edu/.../Lecture_11_Hearing_and_Equilibrium.pdfPhysiology of hearing Sounds set up vibrations in air that beat against the