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AHNNA > L19: Anatomy of the ear > Flashcards

L19: Anatomy of the ear Flashcards

1
Q

What are the functions of the ear?

A
  • hearing

- balance

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2
Q

What are the 3 key regions of the ear?

A
  • external
  • middle
  • inner
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3
Q

What are some signs and symptoms that a patient has ear pathology?

A

Symptoms of ear disease can be varied

  • otalgia (ear pain)
  • discharge
  • hearing loss (conductive vs sensorineural)
  • tinnitus
  • vertigo
  • facial nerve palsy
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4
Q

What is found in the external ear?

A

-pinna (ear we see on outside of head)
-external auditory meatus (ear canal up to the lateral surface of the tympanic membrane)
It is skin lined

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5
Q

What is found in the middle ear?

A
  • air filled cavity
  • has an intermittant connection to the nasopharynx via the pharyngotympanic tube, allows the air filled cavity to equilibriate with atmospheric pressure
  • 3 ossicles which are lined with respiratory epithelium (pseudostratified columnar ciliated with goblet cells)
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6
Q

What is found in the inner ear?

A
  • cochlea (where AP’s are generated to send signals to brain to be perceived as sound)
  • semicircular canals (3, fluid filled, carry AP’s to brain to be detected as balance)
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7
Q

Why do you get referred pain to the ear?

A 
There are many nerves which carry general sensation from the ear
Branches of:
-cervical spinal nerves (C2/3)
-vagus 
-trigeminal (auriculotemporal branch)
-glossopharyngeal (tympanic nerve)
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8
Q

What are the two types of otalgia?

A

-non-otological OR otological in origin

Otalgia with a normal ear examination should lead you to suspect an alternative site of pathology

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9
Q

What are some non-otological causes for otalgia?

A
  • temporomandibular joint dysfunction (CN Vc)
  • diseases of larynx and pharynx, including cancers (CN9/10)
  • diseases of oropharynx (CN9)
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10
Q

What is the function of the external ear?

A

Collects, transmits and focuses sound waves onto the tympanic membrane, causing the tympanic membrane to vibrate
-pinna is cartilaginous with skin, but parts are fatty tissue

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11
Q

What is the structure of the external auditory meatus?

A
  1. 5 cm long in adult
    - skin lined cul-de-sac (lined with keratinising stratified squamous epithelium continuous onto lateral surface of the tympanic membrane)
    - it extends into the petrous bone, so the inner 2/3 is bony and the outer 1/3 is cartilaginous
    - outer part has hair, sebaceous and ceruminous glands (produce wax) which act as a barrier to forgein objects (bony part lacks these)
    - sigmoid shape (pull on pinna in ear exam to straighten it)
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12
Q

What are some abnormalities associated with the pinna?

A

Congenital
Inflammatory
Infective- perichondritis (perichondrium overlies the cartilage and is vascular)
Trauma- pinna haematoma (cauliflower ear)
(facial nerve palsy- Ramsay-hunt syndrome causing unilateral facial droop and red ear with vesicles)

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13
Q

What is a pinna haematoma?

A

Accumulation of blood between the cartilage and its overlying perichondrium from blunt injury

  • common in contact sports
  • causes a subperichondrial haematoma which strips the perichondrium off the cartilage, this deprives the cartilage of its blood supply, and increased pressure can lead to pressure necrosis of tissue
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14
Q

How do you treat a pinna haematoma?

A

-drainage
-prevent re-accumulation/re-apposition of the 2 layers
If untreated, cartilage is starved of blood supply, so you get scarring, fibrosis, and new asymmetrical cartilage development = cauliflower ear

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15
Q

What is a special function of the external acoustic meatus?

A

Self cleaning function keeping the ear canal free of debris

-epithelial migration (surface of the skin moves laterally from the surface of the tympanic membrane)

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16
Q

How do we view the external auditory meatus?

A

Otoscope

  • can see wax/forgein bodies
  • otitis externa (inflammation of the external ear, often called swimmers ear because the risk factor for this is moisture in the ear which provides ideal breeding ground for bacteria)
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17
Q

What are the features of a normal otoscopic view?

A
  • cone of light (reflecting from otoscope)
  • large extend is the pars tensa
  • less tense part at superior edge is the pars flaccida
  • manubrium of the malleus (attachment of the first of the ossicles to attach to the tympanic membrane)
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18
Q

What is a rare complication found with otitis externa?

A

Malignant otitis externa

  • rare
  • very serious/life threatening
  • infection becomes invasive and erodes through bone of the ear
  • risk for those who are immunocompromised, including diabetics
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19
Q

What are some common abnormailities involved with the tympanic membrane?

A

Normal appearance is concave, with central dip pointing towards middle ear cavity

  • tympanosclerosis (scarring of tympanic membrane)
  • bacterial acute otitis media: bulging laterally due to inflammatory exudate
  • otitis media with effusion: not caused by infection, causes membrane to become retracted, may see evidence of fluid due to presence of bubbles/fluid level seen (also called glue ear)
20
Q

What is cholesteatoma?

A

Rare but should not be missed

  • retraction of pars flaccida due to increased negative pressure inside the middle cavity (there shouldn’t be due to the eustchian tube equilibrating) to form a sac/pocket
  • traps stratified squamous epithelium and keratin (migration is prevented)
  • this then proliferates forming a cholesteatoma

Secondary to chronic eustachian tube dysfunction

  • painless
  • smelly otorrhea (ear discharge)
  • may be hearing loss (it grows and expands so the ossicles may get damaged)
  • cause enzymatic bony destruction eroding ossicles/mastoid or petrous bone/cochlea (can damage sigmoid sinus as found on edge of petrous bone)
21
Q

What are the 3 ossicles found in the middle ear?

A

-malleus
-incus
-stapes (communicates with membrane on cochlea known as the oval window)
(lateralto medial: MIS)

Ossicles are connected via synovial joints

  • amplify (due to difference in SA b/w the TM and the oval window) and relay vibrations from the tympanic membrane to the oval window of the cochlea
  • ossicle movements are ‘tampered’ (if there is a very large sound) by 2 muscles: tensor tympani and the stapedius (protective)
22
Q

Why do the vibrations in the ear need to be amplified?

A

Because the vibrations are travelling from ear to fluid

23
Q

What is the acoustic reflex?

A

Stapedius (facial nerve supplies this) muscle contracts to dampen the vibration in response to very loud noises

24
Q

What is otosclerosis?

A

One of the most common causes of acquired hearing loss in young adults

  • genetic and environmental causes
  • ossicles fuse at articulations (synovial joints) due to abnormal bone growth (particularly b/w base plate of stapes and oval window)
  • fusion means there is less movement so sound vibrations can’t be transmitte effectively to cochlea
  • present with gradual unilateral/bilateral conductive hearing loss
25
Q

What is another name for the pharyngotympanic tube?

A

Eustachian tube

-equilibriates pressure of middle ear with atmospheric pressure

26
Q

What is a special feature of the mucous membrane of the middle ear?

A

Continuously absorbs air causing a negative pressure

-this would affect the ability of the TM to vibrate normally, and the ability of the ossicles to move

27
Q

What is otitis media with effusion?

A
  • TM is retracted
  • may see fluid
  • not an actual infection, but can predispose to
  • due to eustachian tube dysfunction
  • fluid and negative pressure inside the ear (fluid is present as it draw fluid across the mucus membrane into the cavity)
  • hearing loss
  • most resolve spontaneously in 2-3 months
  • intervene is persists longer than 3 months
28
Q

How do you treat otitis media with effusion?

A

Grommets (tympanostomy tube)

-placed throught the tympanic membrane to allow equilibration of pressure

29
Q

What is acute otitis media?

A 
Acute middle ear infection
-common in infants
Signs/symptoms:
-otalgia (infants pull/tug ear)
-non-specific symptoms (fever)
-red +/- bulging TM and loss of normal landmarks
30
Q

What causes acute otitis media?

A

Viral aetiology

e. g. streptococcus pneumoniae (common)
e. g. haemophilus influenzae

31
Q

Why are infants more susceptible to middle ear pathologies?

A

-eustachian tube is shorter and more horizantal in infants
Therefore
-easier passage for infection from nasopharynx to middle ear
-tube can block more easily, compromising ventilation and drainage of middle ear
-around where the eustachian tube connects to the nasopharynx there is collection of lymphatic tissue: pharyngeal tonsils (adenoids), which can be large and cause obstruction to tube (adenoids tend to atrophy as you get older)

32
Q

What are the complications of acute otitis media?

A
  • TM perforation
  • facial nerve involvement
  • mastoiditis (middle ear cavity communicates via mastoid antrum with mastoid air cells)- may cause ear to be pushed forward due to inflammation
  • intracranial complications (meningitis)
33
Q

What occurs in the cochlea of the ear?

A
  • Fluid movement (generated by the footplate of the stapes)

- Converted into AP’s (down vestibulocochlear nerve) > perceived as sound

34
Q

What occurs in the vestibular apparatus?

A
  • fluid movement (generated by the position/rotation of head)
  • converted to AP’s (down vestibulocochlear nerve) > perceived as position sense and balance
35
Q

What do diseases of the inner ear present with?

A
  • hearing loss (sensorineural)
  • tinnitus
  • disturbances of balance and vertigo
36
Q

What is the structure of the cochlea?

A

Fluid filled tube with specialised hair cells that generate action potentials when moved

  • arranged in spiral, housed within the petrous part of the temporal bone
  • fluid filled tube which lies within the hollowed out shape of the petrous bone is the cochlear duct
37
Q

How does the fluid move in the cochlea?

A

Oval window (membrane) attached to footplate of stapes

  • when stapes vibrates, so does the oval window
  • causes movement of fluid within the cochlear duct
  • waves of fluid cause movement of special sensory cells (stereocilia) which generate AP’s via CN8 to the brain
38
Q

Where do you find the stereocilia?

A

In the cochlear duct in a part called the spiral organ of Corti
-movements in cochlear fluid are sensed by sterocilia

39
Q

What is the structure of the vestibular apparatus?

A
  • semicircular canals/ducts (anterior, posterior and lateral which are orientated in the 3 planes in which we can move our head), saccule and utricle
  • full of fluid and contain stereocilia
  • moving position/rotation of the head moves the fluid, which bends stereocilia, generating AP via CN8 to the brain
40
Q

What is the fluid that fills the ducts in the ear?

A

Endolymph

41
Q

What is presbycusis?

A

Sensorineural hearing loss associated with old age (age related deterioration in structures related to hearing)
-bilateral and gradual
-due to age related changes
-can be corrected with hearing aids
No involvement of the vestibular structures

42
Q

What is benign paroxysmal positional vertigo? (BPPV)

A

Vertigo only (affects only vestibular apparatus)

  • short-lived episodes (seconds) triggered by movement of head
  • caused by crystals that form in the tubes of the vestibular apparatus and these can dislodge and cause movements of stereocilia
43
Q

What are some conditions that affect the cochlear and vestibular apparatus?

A

Meniere’s disease

  • vertigo/tinnitus/hearing loss
  • usually unilateral
  • may describe ‘aural fullness’, nausea and vomiting
  • symptoms last longer (30 mins-24hrs)
  • recovery between recurrent episodes
  • hearing may deteriorate over time as well as hearing dips during episodes

Acute labrynthitis

  • history of upper respiratory tract infection
  • involvement of ALL inner ear structures (hearing loss/tinnitus/vertigo/vomiting)

Acute vestibular neuronitis

  • history of upper respiratory tract infection
  • no hearing disturbances or tinnitus
  • only involves vestibular part
  • sudden onset of vomiting and severe vertigo (lasting days)
44
Q

What do you do when someone presents with hearing loss?

A
  • take history
  • examination (inspection and palpation of external ear, otoscopy)
  • gross hearing assessment (whispering)
  • tuning fork tests (Weber’s and Rinne’s test)
  • formal audiometry testing
45
Q

Why are tuning fork tests important?

A

Determine whether is it the inner ear/middle ear pathology

-sensorineural (inner) vs conductive hearing loss

46
Q

What causes conductive hearing loss?

A

Pathology involving the external/middle ear

  • wax
  • acute otitis media
  • otitis media with effusion
  • otosclerosis
47
Q

What causes sensorineural hearing loss?

A

Pathology involving the inner ear structures or CN8

  • presbycusis
  • noise-related hearing loss (bilateral and gradual)
  • Meniere’s disease
  • ototoxic medications (furosemide)
  • acoustic neuroma (benign tumour on vestibular component of CN8): unilateral hearing loss

AHNNA (25 decks)

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