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Anatomy And Physiology Of The Ear > ANATOMY AND PHYSIOLOGY OF THE AUDITORY SYSTEM > Flashcards

ANATOMY AND PHYSIOLOGY OF THE AUDITORY SYSTEM Flashcards

1
Q

Divisions of the ear

A

Peripheral Auditory System * Outer Ear
* Middle Ear * Inner Ear
* Cochlea
* VestibularSystem
Peripheral
* Central Auditory System
* Auditory Nerve
* Auditory Nuclei and Pathways (8CSLIMA)

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2
Q

The Peripheral Auditory System

A

Outer Ear
* Acoustic e n e r g y
Middle Ear
*Mechanical energy
Inner Ear
* Hydro-neural energy

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3
Q

Outer ear

A

-Pinna (Auricle)
-External auditory
meatus

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4
Q

Pinna – Anatomy

A

Pinna
* Funnel shaped
* Composed of cartilage
* Attached to cranium by ligaments
* Landmarks * Concha
* Helix * Tragus * Lobe

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5
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
Non Acoustic
* Protects entrance into EAC

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6
Q

External Auditory Canal – Anatomy

A

2.5cmlong(1”) * S-shaped
* Outer1/3
* Cartilaginous
* Skin contains hair follicles * Cerumenous / sebaceous
glands * Inner2/3
* Bony&narrower
* Osseocartilaginousjunction

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7
Q

External Ear Physiology

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 amplifier

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8
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 s, sh, t
    and f?
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9
Q

Neuro-reflexes of the EAC

A

*
Neuro-reflexes of the EAC
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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10
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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11
Q

External Ear Disorders

A
  • Cerumen Impaction
  • ForeignBodiesOcclusion
  • Infections
  • Growths/Tumors
  • Exostoses - benign, associated with exposure to cold water
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12
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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13
Q

Tympanic Membrane

A

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

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14
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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15
Q

Tympanic Membrane Physiology

A
  • Vibrates in response to sound pressure waves
  • Changes acoustical energy into mechanical energy
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16
Q

Disorders of the Tympanic Membrane

A
  • Perforation
  • Trauma
  • Barotrauma
  • Infection
  • Acoustic Trauma
    · Tympanosclerosis - > History of e a r infections
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17
Q

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! Malleus , incus , Stapes
  • 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)
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

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.
26
Q

ME Transformer/Amplifier

A
  • 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
27
Q

ME Transformer/Amplifier

A

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

28
Q

Middle Ear Disorders

A
  • Otitis Media
  • Cholesteatoma
    *Ossicular Disarticulation -> Breaks and no longer moving with each other
  • Otosclerosis
29
Q

Inner Ear – Anatomy of the Cochlea

A
  • Osseous (bony)labyrinth
  • Membranous labyrinth
    -Auditory labyrinth
    -Vestibular labyrinth
30
Q

Cochlear Anatomy

A
  • 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
31
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
32
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
  • 13-15,000OHC
  • Inner hair cells – 1 row
  • 3000–3500IHC * Stereocilia
    300px-Cochlea-crosssection
  • Hairlike projections on top of hair cells
33
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

34
Q

Traveling Wave

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
    Endolymph K+ ions
    42
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

Hair Cell 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

Disorder of the Inner Ear

A

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

41
Q

Disorder of the Inner Ear
*Congenital
*Head Trauma
*Noise Induced HL *Infections
*Presbycusis *Ototoxicictiy
*Meniere’s Disease *Sudden SNHL (idiopathic)
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
42
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
43
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
44
Q

CANS FEATURES

A
  • Tonotopic organization
  • Preserved throughout the entire auditory pathway
    *AfferentPathway To the brain
  • 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 56
45
Q

Afferent Central Auditory Pathways - 8CSLIMA

A
  • 8th Craniel Nerve
  • Cochlear Nucleus
  • Superior Olivary Complex * Lateral Lemniscus
  • Inferior Colliculus
  • Medial Geniculate Body
  • Auditory Cortex
46
Q

Central Auditory Pathways

A

Ipsilateral
* CochlearNucleus sounds travel ipsilaterally
* Auditory nerve fibers terminate in the
ipsilateral cochlear nucleus
Contralateral
* Superior Olivary Complex or Nucleus
* First relay station that receives ipsilateral
and contralateral fibers from both cochlear
sound reaches over to other side 1st point of decasation
nuclei
* Fx - Localization (time and intensity cues)
* Fx- Mediates acoustic reflex activity

47
Q

Central Auditory Pathways

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
48
Q

Primary Auditory Cortex

A
  • Temporal Lobe * Heschl’s Gyrus)
  • Tonotopically mapped * Auditory Perception
49
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.
    In order for sound to come to life, the signal has to be shared with other parts of the brain in order to make sense
50
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.
51
Q

Disorders of the VIIIth Nerve & Central Auditory Nervous System

A
  • Acoustic Nerve Tumor
  • Neurofibromatosis (Benign slow growing
    Unilateral hearing loss tinnitus)
  • Auditory Neuropathy
  • CentralAuditoryProcessingDisorder
  • HereditaryMotor-SensoryNeuropathies * CharcotMarieTooth
  • FriedrichsAtaxia
  • Cerebral Vascular Accidents – Disruption of blood supply to brain - UHL

Anatomy And Physiology Of The Ear (2 decks)

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