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Advance Audiology > ANATOMY AND PHYSIOLOGY OF THE AUDITORY SYSTEM > Flashcards

ANATOMY AND PHYSIOLOGY OF THE AUDITORY SYSTEM Flashcards

1
Q

Structure of the auditory system
Location

A
  • Contained in the temporal
    bone
  • Located on the sides of
    the skull
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2
Q

Divisions of the ear

A
  • ____peripharal_________ Auditory System
  • Outer Ear
  • Middle Ear
  • Inner Ear
  • Cochlea
  • Vestibular System
  • _____central_________ Auditory System
  • Auditory Nerve
  • Auditory Nuclei and Pathways (8CSLIMA)
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3
Q

The Peripheral Auditory System

A
  • ___outer____Ear
  • __acoustic ____energy
  • ___middle____Ear
  • ___mechanic___energy
  • __inner_____ Ear
  • ____hydro/neuro__energy
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4
Q

Outer ear

A

*Pinna (Auricle)
*External auditory
meatus

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5
Q

Pinna

A
  • Pinna
  • Funnel shaped
  • Composed of cartilage
  • Attached to cranium by
    ligaments
  • Landmarks
  • Concha
  • Helix
  • Tragus
  • Lobe
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6
Q

Pinna Physiology

A

Acoustic
* Collects and funnels sound from the
environment into the ear canal
* Enhances high frequency sounds

Sound localization
* Is sound above or below, front or back or
from right side or left side
N
on Acoustic
* Protects entrance into EAC

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7
Q

External Auditory Canal – Anatomy

A
  • 2.5 cm long (1”)
  • S-shaped
  • Outer 1/3
  • Cartilaginous
  • Skin contains hair follicles
  • Cerumenous / sebaceous
    glands
  • Inner 2/3
  • Bony & narrower
  • Osseocartilaginous junction
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8
Q

External Ear Physiology
Acoustic vs non acoustic

A

Non acoustic:
* Protection of Tympanic Membrane
* Cerumen
* Length and shape of ear canal
* Lubricates ear
* Protects ear from foreign objects
Acoustic:
* Sound Collection – Directs sound to TM
* High Frequency amplifie

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9
Q

Combined External Ear Resonance

A
  • Influence of pinna (p)
  • Influence of ear canal (m)
  • Combine influence (t)
  • At about 3000 Hz, the final
    amplification (t) is 20 dB
  • Helpful in discriminating high
    frequency fricative
    consonants such as __ __ __
    and ___?
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10
Q

Neuro-reflexes of the EAC
3

A
  • Vagus Reflex -Arnold’s branch of the vagus (CN X)
    ▪ Cough or gag reflex
    ▪ Evoked during insertion of otoblock, wax removal, otoscopy

▪ Trigeminal Reflex – (CN V)
▪ Red Reflex
▪ Can cause excessive vascularization and
thickening of TM during otoscopy

▪ Lymphatic Reflex - (Cranial V and VII)
▪ Excessive swelling of tissues and soreness while wearing a custom mold or HA
▪May be due to allergic reaction or result of a poor fit

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11
Q

Outer Ear Malformations

A

• Microtia: A condition where the outer ear is smaller than normal.

•	Anotia: A condition where the outer ear is completely missing.

•	Atresia: The ear canal is either closed or missing, affecting hearing.

•	Low set ears: Ears that are positioned lower than usual on the head.

•	Abnormally formed ears: Ears that have an unusual shape or structure.

•	Pits and tags: Small holes (pits) or extra bits of skin (tags) near the ears.
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12
Q

External Ear Disorders

A
  • Cerumen Impaction
  • Foreign Bodies Occlusion
  • Infections
  • Growths/Tumors
  • Exostoses - benign, associated
    with exposure to cold water
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13
Q

Syndromes Associated with OE Malformation

A

◼ Down Syndrome
◼ Turner Syndrome,
◼ Treacher Collins
◼ DiGeorge Syndrome
◼ Charge Syndrome
◼ Trisomy 13 and 18 Syndrome
◼ Goldenhar Syndrome (oculo-auriculo-vertebral spectrum)

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14
Q

Tympanic Membrane

A

AKA
* Eardrum
* Tympanum
* Border between
outer ear and middle
ear

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15
Q

Tympanic Membrane Anatomy

A
  • Semi transparent oval, cone shaped membrane
  • Composed of 3 layers
    *Outer – continuous with skin of bony canal
    *Middle – Fibrous connective tissue
    *Inner – Continuous with mucous membrane of ME
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16
Q

Disorders of the Tympanic Membrane

A
  • Perforation
  • Trauma
  • Barotrauma
  • Infection
  • Acoustic Trauma
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17
Q

The Middle Ear
What’s the name of the roof of the middle ear?

A
  • Air filled cavity behind the eardrum about 2
    cm3.
  • The roof of the middle ear, the tegmen
    tympani, is a thin layer of bone, separating
    the middle-ear cavity from the brain.
  • Surrounded by mastoid bone
  • Lined with mucous membrane
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18
Q

Middle ear anatomy

A
  • Eustachian Tube
  • Connects middle ear to nasopharynx
  • Ossicular Chain
  • Name those bones!
  • Stapedial Muscle
    o Stapedius – attached to stapes
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19
Q

Middle Ear Physiology

A

Conduction
Conduct sound from the outer ear to the inner ear
Transducer
Converts acoustic energy to mechanical energy
Protection
Middle ear muscles may? provide protection from loud sounds
Pressure Equalizer
Equalizes pressure between middle ear cavity and nasopharynx
Amplifier
Impedance Matching Transformer
Matches the transfer of energy between air to fluid

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20
Q

Eustachian Tube Physiology

A
  • Equalizes pressure in the middle ear
    cavity so that it remains air filled.
  • Fluid drainage from ME into
    Nasopharynx
  • The ET is shorter and wider in length
    in children compared to adults
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21
Q

Ossicular Chain (Malleus, Incus and
Stapes)

A
  • Smallest skeletal bones in the body.
  • Connected to the medial wall of the TM
    and articulate with each other
  • Each ossicle is suspended
    independently by ligaments
  • Purpose – delivers sound vibrations
    efficiently to the inner ear (cochlea)
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22
Q

Middle Ear Muscles

A

Stapedius Muscle
* Attached to the Stapes
* Innervated by CN VII
* Acoustic or Stapedial Reflex –
contracts to loud sounds
* Stiffens the ossicular chain and
decreases sound energy to the inner
ear.
* Absent acoustic reflex could signal CHL
or SNHL

23
Q

The (Impedance Mismatch) Problem

A
  • Hearing requires a transfer of acoustic energy from low
    impedance air-borne soundwaves to high impedance fluid
    vibrations in the cochlea.
  • Sound intensity is lost due to impedance mismatch created
    by the change of sound traveling from air medium to a
    (cochlear) fluid medium!
24
Q

The (Impedance Mismatch) Solution

A
  • An impedance matching
    transformer to allow
    efficient transfer of energy
    between the two media of
    different physical
    properties!
25
Q

ME Transformer/Amplifier
* Area Ratio Advantage
Laver action

A
  • Area Ratio Advantage
  • The area of the tympanice membrane is much larger than
    the oval window
  • Area of TM is 17X larger than Ow
  • Difference between surface are of TM (55mm) and
    Stapes footplate (3.2mm) results in increase in sound
    pressure of approximately 25 dB of the impedance
    mismatch.

ME Transformer/Amplifier
* Lever Action
* The length of the long arm of the
malleus is much longer than the long
arm of the incus
* Difference in length produces a lever
action that amplifies sound pressure
and accounts for about 2 dB of the
mismatch
31
32

26
Q

ME Transformer/Amplifier
*Curved Membrane
By how much dB amplification?

A

*Curved Membrane
* TM’s curved shape concentrates
energy toward middle where
TM is attached to malleus and
accounts for 3 – 6 dB

27
Q

Middle Ear Disorders

A
  • Otitis Media
  • Cholesteatoma
  • Ossicular Disarticulation
  • Otosclerosis
    1. Otitis Media: An infection or inflammation of the middle ear, often causing ear pain and sometimes fluid buildup behind the eardrum.
    2. Cholesteatoma: An abnormal, non-cancerous growth of skin cells in the middle ear that can damage surrounding bones and tissues.
    3. Ossicular Disarticulation: A separation or break in the chain of tiny bones (ossicles) in the middle ear, leading to hearing loss.
    4. Otosclerosis: A condition where abnormal bone growth in the middle ear impairs the movement of the stapes bone, causing hearing loss.
28
Q

Inner Ear – Anatomy of the Cochlea
The different type of labyrinth

A
  • Osseous (bony)labyrinth
  • Membranous labyrinth
    -Auditory labyrinth
    -Vestibular labyrinth
    Factoid - Inner ear reaches its full adult size when the fetus is 20-22 weeks old!
29
Q

Cochlear Anatomy

A

Cochlear Anatomy
* Snail shaped fluid filled cavity within
mastoid bone
* 2 5/8 turns; 35mm long
* Coiled around central core of bone called
the modiolus
* Auditory nerve exists through the modiolus
* Contains 3 fluid filled chambers

30
Q

Cochlear ducts

A
  • Scala vestibuli
  • Upper compartment behind oval window
  • Perilymph (Rich in sodium ions)
  • Scala tympani
  • Lower chamber exits at round window
  • Perilymph (Rich in sodium ion)
  • Scala media
  • Middle chamber
  • Endolymph (Rich in potassium ions)
  • Contains the Organ of Corti
  • Two membranes
  • Reissner’s membrane
  • Basilar membrane
31
Q

Organ of Corti

A
  • Located in the scala media
  • Rests on basilar membrane
  • Tectorial membrane
  • Jelly like substance that rests across top of
    hair cells
  • Hair cells
  • Outer hair cells – 3 rows
  • 13-15,000 OHC
  • Inner hair cells – 1 row
  • 3000 – 3500 IHC
  • Stereocilia
  • Hairlike projections on top of hair cells
32
Q

Inner Ear Physiology

A

Traveling Wave
* Stapes footplate pushes oval window in and displaces fluid causing
outward displacement of the round window
* Fluid movement creates a traveling wave on the basilar membrane
* Maximum displacement of the traveling wave is frequency dependent
* The traveling wave progresses from base to apex causing shearing or
bending of the hair cells in the tectorial membrane

33
Q

Traveling Wave
Tonotopic organization

A

Tonotopic Organization
* Different areas of the basilar
membrane are sensitive to different
frequencies
* Base: High frequency
* Basilar membrane is narrow and
stiff
* Apex: Low frequency
* Basilar membrane is wide and
flexible

34
Q

Traveling Wave
Tonotopic Organization

A

Tonotopic Organization
* Different areas of the basilar
membrane are sensitive to different
frequencies
* Base: High frequency
* Basilar membrane is narrow and
stiff
* Apex: Low frequency
* Basilar membrane is wide and
flexible

35
Q

Shearing of the Haircells

A
  • Tip links between cilia of the hair cells act
    as mechanical gates.
  • The endolymph surrounding the hair cells
    contain charged potassium ions
  • No sound – tip link remains closed and
    charged potassium ions are not allowed in
36
Q

Shearing of the Haircells

A

Sound is present - traveling wave causes the hair cells to
bend, tip links (gates) open, and charged potassium ions
flow into the haircells.
* Neurotransmitter vesicles drop to the base of the cell and
and release glutamate into the synaptic space and stimulates
the auditory nerve fibers.
* Neural impulses transmit the signal through the nerve,
up the auditory pathways, towards the brain.

37
Q

Outer Hair Cells

A

3 rows, 13,000 OHCs, test tube shaped
*Cilia are imbedded in tectorial
membrane

*Cochlear amplifier
* Sensitive to soft input sounds up to 60 dBHL
*Expand and contract to mechanically amplify low level sounds
to stimulate IHC

*Frequency resolution – Sharpens peak of traveling
wave
*Efferent fibers (generates otoacoustic emissions)
*Encode sound intensity

38
Q

Inner Hair Cells

A

*1 row, 3500 IHCs, pear or flask shaped
*Cilia are not touching tectorial membrane
*Sends signals to auditory N. when
stimulated
*Do not sense sounds softer than
conversational speech above 60 dB HL
*Afferent nerve fibers
*Encode sound clarity

39
Q

OHC Damage

A

HL up to 60 dB HL
* Recruitment – Abnormal growth in
loudness
* Soft sounds below conversational
speech (50-60dBHL) are inaudible
* Loud sounds are perceived as loud
as to someone with normal
hearing
* Difficulty understanding speech in noise
due to poor frequency resolution

40
Q

IHC Damage

A
  • Losses greater than 60dB HL,
    most likely involve outer and IHC
    damage
  • Greater sound distortion
41
Q

Disorder of the Inner Ear

A

*Congenital
*Head Trauma
*Noise Induced HL
*Infections
*Presbycusis
*Ototoxicictiy
*Meniere’s Disease
*Sudden SNHL (idiopathic)

42
Q

Acoustic (8th C.) Nerve

A
  • Two branches
  • Cochlear portion
  • Vestibular portion
  • Auditory nerve fibers exit cochlea through modiolus
  • Cochlear branch joins with vestibular branch, passes
    through internal auditory meatus, and terminates at base
    of brain
43
Q

Auditory Nerve

A
  • Extends 17-19 mm beyond the internal auditory
    canal
  • Attaches to the brainstem at the cerebellopontine
    angle (CPA-area in the brainstem where cerebellum,
    medulla and pons are joined)
  • Auditory nerve fibers terminate in the cochlear
    nucleus of the brainstem
  • Tonotopic Organization is preserved
  • High frequencies – outer part of auditory nerve
  • Low frequencies – middle part of auditory nerve
44
Q

CANS FEATURES

A
  • Decussation
  • Crossing over from one side to the other
  • Each hemisphere of the brain processes information from both ipsilateral (same
    side) and contralateral (opposite side) sides
  • Fibers that originate in the left ear synapse on the right side of the brain and
    vice versa
  • Thus, information from one ear, reaches both sides of the brain
  • Brain damage in one hemisphere has little effect on peripheral hearing.
  • Improves processing of complex speech
45
Q

CANS FEATURES

A
  • Tonotopic organization
  • Preserved throughout the entire auditory pathway
  • Afferent Pathway
  • Sound travels from the cochlea UP to the auditory
    nerve, then to the brainstem and then to the brain.
  • Efferent Pathway
  • Descending nerve fibers from the brain to the
    brainstem and cochlea (not well understood)
  • Primary and secondary auditory Cortex
46
Q

Afferent Central Auditory
Pathways - 8CSLIMA

A
  • 8th Craniel Nerve
  • Cochlear Nucleus
  • Superior Olivary Complex
  • Lateral Lemniscus
  • Inferior Colliculus
  • Medial Geniculate Body
  • Auditory Cortex
47
Q

Central Auditory Pathways

Cochlea nucleus
Superior Olivary Complex or Nucleus

A
  • Cochlear Nucleus
  • Auditory nerve fibers terminate in the
    ipsilateral cochlear nucleus
  • Superior Olivary Complex or Nucleus
  • First relay station that receives ipsilateral
    and contralateral fibers from both cochlear
    nuclei
  • Fx - Localization (time and intensity cues)
  • Fx- Mediates acoustic reflex activity
48
Q

Central Auditory Pathways

Lateral Lemniscus
Inferior Colliculus
Medial Geniculate Body

A
  • Lateral Lemniscus
  • Carries auditory fibers from the superior
    olive to the inferior colliculus.
  • Involved in acoustic startle reflex
  • Inferior Colliculus
  • Obligatory relay station of the ascending
    auditory pathway
  • Medial Geniculate Body
  • Last subcortical relay station in ascending
    pathway
49
Q

Primary Auditory Cortex

A
  • Temporal Lobe
  • Heschl’s Gyrus)
  • Tonotopically mapped
  • Auditory Perception
50
Q

Secondary (Associated) Auditory Cortex

A
  • Surrounds primary area and receives impulses
    from the primary auditory area
  • Integrates and associates sound with other
    sensory areas of for interpreting and
    understanding the meaning of sounds.
  • Interhemispheric fiber tracts – delivers sound
    to different areas of the brain
  • Arcuate Fasciculus delivers sound to the frontal
    lobe.
51
Q

Landmark Studies of Auditory Brain Development

A

Green et al., 2005
* Measured PET scan while post-lingually deafened adult
cochlear implant users listened to a story.
* Showed activation of right and left primary and association
auditory areas.
* The normal listening brain shows bilateral activation of the
primary and secondary auditory cortex

52
Q

Landmark Studies of Auditory Brain Development

A

Nishimura et al., 1999
* Used PET to evaluate areas of brain that are active in pre-lingually deafened adults who
use ASL and received CI in adulthood
* Story told via hand movements in meaningless fashion showed responsiveness in the
occipital area of the brain
* Story via sign language showed robust activity in secondary cortex
* Story with audition alone showed activity in the primary auditory cortex only.
* Evidence of cross modal plasticity due to sound deprivation during the formative years
of life

53
Q

Key Points - Auditory Deprivation and Cross
Modal Plasticity

A
  • Primary auditory cortex is reserved for hearing sound. There is
    little evidence of cross-modal plasticity.
  • Cross Modality plasticity – the brain reorganizes itself to receive
    input from other senses, primarily vision
  • Cross Modal plasticity occurs in the second auditory cortex.
  • When an individual who is deprived of sound in the formative years
    hears sound, it is stuck in the primary auditory cortex.
  • The secondary auditory cortex is processing other types of stimuli.
    Sound will not be delivered to other areas of the brain for higher-
    order meaning

Advance Audiology (5 decks)

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