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The ear Flashcards

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1
Q

List the functions of the ear

A
  • Locate directional source of sound
  • Collect sound waves and conduct to inner ear
  • Transduction and transmission of impulses to brain
  • Balance and positional sense
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2
Q

What are the 3 levels of the ear?

A
  • External
  • Middle
  • Inner
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3
Q

Describe the anatomy of the auricular cartilage

A
  • Flattened distally
  • Ridged proximally to form anthelic and tragus
  • Changes from cone shaped to tube shaped proximally, concha
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4
Q

Describe the anatomy of the scutiform cartilage

A
  • Rostromedial

- Function is support

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5
Q

What are the limits of the external ear?

A

Pinna and external ear canal (external auditory meatus) down to tympanic membrane (ear drum)
- L shaped

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6
Q

Describe the anatomy of the annular cartilage

A
  • Ring shaped

- Attaches other cartilages to bone of bulla

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7
Q

Describe the anatomy of the acoustic process

A
  • Ligamentous attachments to skill

- Attaches to cartilages

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8
Q

What is the vascular supply to the external ear?

A
  • Auricular arteries (from internal carotid)

- Venous drainage to internal maxillary vein

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9
Q

Describe the innervation of the external ear

A
  • Motor nerves to auricular muscles (auriculopalpebral branch of CN VII facial)
  • Sensory: branch of CN V trigeminal, cervical segmental C2
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10
Q

What structures are adjacent to the external ear?

A
  • Parotid salivary gland
  • Blood vessels (auricular artery, superficial temporal arteries, branches of external carotid, external maxillary vein)
  • Nerves
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11
Q

What nerves run close to the external ear?

A
  • Facial nerve (rostroventrial to horizontal canal)

- Auriculotemporal branch of mandibular portion of trigeminal nerve (rostral to vertical canal)

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12
Q

Describe the integumentary covering of the external ear

A
  • Tightly adherent, except Henri’s pocket on caudal pinnal edge
  • Thin, squamous stratified keratinising epidermis
  • Thin dermis containing adnexal structures
  • Hair follicles variable density
  • Glands present
  • Connective tissue underneath and tehn cartilage
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13
Q

Describe the glands of the external ear

A
  • Sebaceous more prominent distally
  • Apocrine, ceruminous
  • Increased density proximally
  • Sebaceous glands closer to epidermis than apocrine
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14
Q

Describe the histological appearance of the sebaceous glands of the external ear

A

Large foamy appearance, lipid containing cells

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15
Q

Describe the histological appearance of the apocrine glands of the external ear

A
  • Simple cuboidal epithelium

- Watery secretion

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16
Q

Compare the types of secretion in different parts of the external ear canal

A
  • Distally more lipidy (sebaceous glands)

- Proximally more watery (apocrine glands)

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17
Q

Describe hair within the external ear

A
  • Differs by breed and species
  • Sebaceous glands associated with follicles
  • Number of hairs in ear canal does not equate to ear disease
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18
Q

Describe the tympanic membrane

A
  • Epithelial
  • Boundary betwen external and middle ear
  • Stratified keratinising epithelium laterally (outer part)
  • Thin lamina propria
  • Cuboidal mucosal epithelium medially (middle ear side)
  • Scattered secretory goblet cells
  • Pars flaccida and pars tensa present
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19
Q

Describe the normal cleaning mechanism of the tympanic membrane

A
  • Migration of cells centripetally from middle at level of stratum granulosum
  • Upward epithelial migration proceeds distally
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20
Q

Describe the pars flaccida of the tympanic membrane

A
  • Thicker part
  • Dorsorostrally
  • Adjacent to malleus
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21
Q

Describe the pars tensa of the tympanic membrane

A
  • Thinner
  • Centrally
  • Translucent
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22
Q

Describe the appearance of the malleus at the level of the tympanic membrane

A
  • Manubrium of malleus visible
  • C-shaped
  • Closely associated with collagen in lamina propria
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23
Q

Describe the middle ear

A
  • Tympanic cavity in tympanic bulla
  • Contains auditory ossicles
  • Connected to nasopharynx via eustachian tube
  • 3 compartments
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24
Q

What are the 3 compartments of the the middle ear?

A
  • Epitympanum
  • Mesotympanum
  • Hypotympanum
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25
Describe the epitympanum
- Dorsal, smallest compartment | - Contains malleus and incus
26
Describe the mesotympanum
- Tympanic memrbane laterally - Bony promontory medially - 3rd ossicle stapes attached to oval window - Round window and opening to auditory tube
27
Describe the hypotympanum
- Fundus | - Blind ending cavity
28
What is unique about the hypotympanum of the cat
Incomplete bony septum dividing hypotympanum
29
Describe the anatomy of the auditory ossicles
- Supported by ligaments and muscles | - Variation of relative position affects tension of tympanic membrane
30
Describe the integument of the middle ear
- Cuboidal to columnar epithelial lining | - Mucosal origin, secretory goblet cells
31
Describe the location of the eustachian tube
Runs dorsolaterally/ventromedial to the nasopharynx
32
Describe the integument of the eustachian tube
- Pseudostratified, ciliated, columnar epithelium - Density increases towards nasopharynx - Scattered goblet cells - More prominent at tympanic cavity end
33
What is the function of the goblet cells in the eustachian tube?
- Surfactant secretion to keep tube patent | - Lecithin, lipids mucopoysaccharides
34
What nerves run close to the wall of the bulla?
- Facial nerve CNVII - Branches of facial nerve and vagus CNX - Post-ganglionic fibres of cervial sympathetic trunk
35
Describe the path of the facial nerve CNVII with relation to the bulla
- In facial canal in petrous temporal bone - Exposed in dorsal cavity - Then exits via stylomastoid foramen
36
Describe the path of the branches of the facial nerve and the vagus CNX nerves in relation to the bulla
- Form tympanic nerve | - Transverse cavity to form lingual nerve and pre-ganglionic parasympathetic fibres to salivary glands
37
Describe the post-ganglionic fibres of the cervical sympathetic trunk in with respect to the bulla
- Dorsomedial wall of tympanic cavity - In cat runs in dividing septum - Joins CNIV to eye - Diseases leads to Horner's syndrome
38
Describe the inner ear
- Contained within petrous temporal bone - Cochlea, vestibule and semicircular canals - Encased in bony labyrinth of petrous temporal bone
39
What functions is the inner ear responsible for?
- Hearing - Balance - Position and rotation of head in relation to gravitational forces
40
What methods can be used to investigate ear disease?
- Cytology of external ear - Otoscopy - Radiography
41
Describe the normal microflora of the external ear
- Same as skin - Staphylococci - Malassezia in particular
42
Discuss the role of cerumen in aural health
- Provides protective antimicrobial layer | - Contains immunoglobulins and exfoliated cells
43
Describe the composition of cerumen
- Exfoliated cells (squames discarded and shed as part of cerumen) - Sebaceous secretions (high lipid content, various classes of lipids) - Ceruminous (apocrine) gland secretions (more aqueous) - Immunoglobulins IgA, IgG, IgM (mostly IgG)
44
Describe the role of epithelial cell migration in aural health
- Carries exudate in ear to surface removing cerumen and debris - Epithelial cells move laterally from centre of tympanic membrane to periphery - Then desquamate to contribute to production of cerumen - May be impeded by disease
45
Give an example of how middle ear disease may occur
- Producing too much mucus | - Can fill middle ear with fluid
46
What are the consequences of a ruptured tympanic membrane in terms of flushing the ear?
- If ruptured, need to put in ET tube - If not, fluid will go down eustachian tube into pharynx - Will drown patient
47
Define otitis
Inflammation of the ear | - Can be distinguished as externa, media and interna
48
Describe radiographic imaging of the ears
- Dosoventral, rostrocaudal, open mouth - Allows comparisons between left and right sides - In each view, tympanic bulla will be superimposed on other structures
49
Describe the categories that risk factors for ear disease are subdivided into
- Primary factors: initiate inflammation in a normal ear - Predisposing factors: increase risk of otitis externa but don't cause it on their own - Secondary factors: do not induce, but prevent resolution of the disease once established
50
Give examples of primary risk factors for ear disease
- Allergic dermatitis (atopic dermatitis) - Grass awns - Otocariasis - Ectoparasites - Foreign bodies - Keratinsisation disorders
51
Give examples of predisposing factors for ear disease
- Overtreatment (e.g. antibiotics) - Ear pinnae and canal conformation - increased moisture - Trauma - Obstruction - Ear canal stenosis - Tympanic membrane perforation
52
Give examples of secondary risk factors for ear disease
- Opportunistic infection | - Yeast and bacteria
53
What are the indications for carrying out radiography of the tympanic bullae?
- Persistent otitis externa - Signs of otitis media including head tilt - Swellings assocaited with eithe rinfection or neoplasia - Abnormalities of TMJ e.g. dislocation, dysplasia
54
What is the greatest cause of obstruction in radiography of the tympanic bullae?
Body of mandible
55
Describe the positioning for open-mouthed rostrocaudal imaging of the tympanic bullae of the dog
- Dorsal recumbency, pulls and secure forelimbs caudally - Flex neck at atlanto-occipital joint - Hard palate roughly vertical to cassette, nose pointing cranialy so hard palate and beam form 30degree angle - Tongue against lower jaw, secure head - Lower jaw exteneded and secured caudally with bandage - Ensure no axial rotation - Remove ET tube prior to exposure
56
What is teh centring for open-mouthed rostrocaudal radiography of the tympanic bullae in the dog?
The base of the tongue
57
What is the collimation for open-mouthed rostrocaudal radiography of the tympanic bullae in the dog?
- Cranial: interpupillary line - Caudal: in line with chin - Lateral: outer skin surfaces
58
Describe radiographic changes that occur with otitis media
- Increased opacity of normally air filled bulla - Thickening of bulla wall - Sclerosis of petrous temporal bone - Rarely increased size of bulla - Ossification of horizontal canal cartilage
59
Describe the radiographic changes that may occur with neoplasia of the ear
- Lysis and distortion of wall of bulla | - Soft tissue swelling of adjacent region
60
What are the components of an aural examination?
- Assessment of external ear: pinnae, external acoustic meatus - View from outside - Palpation of auditory meatus - Look for erythema, exudate, odour, chronic thickening or lichenification - Otoscopy
61
What may be seen on otoscopy?
- Erythema or hyperplasia of mucosa - Ulceration of mucosa - Exudate - Neoplasms - Foreign bodies - Otodected cynotis (ear mite) - Tympanic membrane
62
Describe the examination of cerumen/exudate for ear mites
- Small amount of liquid paraffin on clean micro sclide - Sample exudate with cotton bud - Transfer to paraffin on slide, break up if needed - Place coverslip on top - View systematically under x4 objective
63
Describe cytology of otic exudate
- Cotton bud into ear canal to level of horizontal canal, sample exudate - Roll sample onto clean slide - Repeat on other ear using clean end/new bud - Put sample on opposite side of slide, label - Stain with DiffQuik
64
What are the signs of damage to the facial nerve?
Facial paralysis
65
What are the signs of damage to the vestibulocochlear nerve?
- Head tilt - Nystagmus - Deafness
66
What are the signs of damage to the sympathetic fibres near the ear?
- Horner's syndrome - Miosis - Ptosis - Enopthlamos - Nictitating membranes protruding
67
What may the presence of rods on ear cytology commonly indicate?
Pseudomonas

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