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neuro 2019 Exam 3 > Ear > Flashcards

Ear Flashcards

1
Q

External ear: auricle (fxn, struture, blood supply, innervation, lymphatic drainage)

A

(pinna)
1. Function: collect airwaves and funnel them into external acoustic meatus.
2. Structure
a. Cartilages (elastic cartilage) – helix, tragus, antihelix
b. Depressions – concha, scaphoid fossa
c. Lobule – composed of fibroelastic tissue
3. Blood supply
a. Posterior auricular a. and v.
b. Superficial temporal a. and v.
4. Innervation
a. Great auricular (C2,C3) and lesser occipital (C2,C3) nn
b. Auriculotemporal nerve (V3), facial n., vagus n.
5. Lymphatic drainage – mastoid, parotid lymph nodes → deep cervical lymph nodes

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2
Q

External ear: external acoustic meatus (defn, histology, blood supply, innervation)

A
  1. Canal traveling through tympanic portion of temporal bone to tympanic membrane.
  2. Lined by stratified squamous epithelium containing numerous ceruminous glands.
  3. Lateral 1/3 is cartilaginous; medial 2/3 is bony
  4. Blood supply
    a. Posterior auricular a. and v.
    b. Superficial temporal a. and v.
    c. Deep auricular a
  5. Innervation
    a. Auriculotemporal nerve (V3)
    b. Vagus n.
  6. Lymphatic drainage – deep cervical lymph nodes.
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3
Q

otitis externa

A

inflammation of the external ear

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4
Q

External ear: Tympanic membrane

A
  1. Function: convert sound waves into vibrations of middle ear ossicles.
  2. Structure
    a. Semitransparent, fibroelastic membrane
    b. Separates external and middle ear.
    c. Covered by epidermis externally; mucus membrane internally.
    d. The membrane is directed anteriorly and inferiorly.
  3. Features
    a. Umbo – central concavity of membrane.
    b. Pars flaccida – superior, thin-walled portion
    c. Pars tensa – inferior, thick-walled portion
  4. Blood supply
    a. External surface – deep auricular branch of maxillary artery
    b. Internal surface – anterior tympanic branch of maxillary artery
  5. Innervation
    a. External surface – auriculotemporal nerve (V3); vagus n.
    b. Internal surface – glossopharyngeal nerve
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5
Q

External ear embryology

A
  1. Auricle
    a. Derived from mesenchyme of first and second pharyngeal arches.
    b. 6 auricular hillocks will later fuse to form the definitive auricle.
    c. CLINICAL CORRELATION: Defects are common and associated with most chromosomal syndromes.
  2. External Auditory Meatus
    a. Derived from first pharyngeal cleft.
    b. Meatal plug forms from proliferation of epithelial cells; by 7th month degenerates.
    c. CLINICAL CORRELATION: Persistence of meatal plug can cause deafness.
  3. Tympanic Membrane
    a. External epithelium derived from ectoderm of first pharyngeal cleft.
    b. Middle connective tissue derived from mesoderm of first pharyngeal arch.
    c. Internal epithelium derived from endoderm of first pharyngeal pouch
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6
Q

Middle ear defn, function

A

A. The middle ear contains the tympanic cavity, a mucous membrane-lined space within the petrous portion of the temporal bone, and the auditory ossicles.

B. Function

  1. Transfer of sound waves from gas to liquid medium (from external to internal ear).
  2. Amplification of sound waves via vibration of bony ossicles.
  3. Protective response to loud sounds (via tensor tympani & stapedius mm).
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7
Q

Middle Ear: Tympanic cavity roof and floor

A
  1. Roof – tegmen tympani; separates epitympanic recess from middle cranial fossa.
  2. Floor – segment of temporal bone separating middle ear from internal jugular v.
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8
Q

Middle ear: tympanic cavity medial and lateral walls

A
  1. Lateral wall – tympanic membrane.
  2. Medial wall – bony wall separating middle from internal ear.
    a. Promontory – mound of bone created by cochlea.
    b. Oval window (fenestra vestibule)
  3. Opens to vestibule of internal ear.
  4. Contacted by the stapes; transmits motion of stapes to fluid of internal ear.
    c. Round window (fenestra cochleae)
  5. Opens to scala tympani; covered with a thin membrane (round window membrane)
  6. Acts as a pressure release valve for the fluids of the internal ear.
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9
Q

middle ear: tympanic cavity posterior wall

A

temporal bone

a. Aditus ad antrum – entrance to the mastoid antrum.
b. Facial canal – for passage of facial n.

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10
Q

Clinical correlation: mastoiditis

A

Middle ear infections can sometimes spread to the mastoid air cells. Infections can then spread superiorly into the middle cranial fossa.

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11
Q

middle ear: tympanic cavity anterior wall

A

segment of temporal bone separating middle ear from carotid canal. Receives opening for pharyngotympanic tube and semi-canal (passage of tensor tympani).

a. Pharyngotympanic tube (auditory tube; eustachian tube)
1. Cartilaginous and membranous tube connecting middle ear and nasopharynx.
2. Function – balances pressure on external and internal sides of tympanic membrane.
3. Posterolateral third is bony; anteromedial 2/3 is cartilaginous.
4. Tensor veli palatini muscle can open the membranous tube (CN V3

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12
Q

Auditory Ossicles

A
  1. Malleus
    a. Contacts tympanic membrane; creates umbo.
    b. Vibrates in response to movement of the tympanic membrane.
  2. Incus
    a. Body articulates with head of malleus.
    b. Long limb articulates with stapes.
  3. Stapes
    a. Base – contacts oval window.
    b. Vibration of stapes induces motion of the fluid within the cochlear duct.
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13
Q

Muscles of the middle ear

A
  1. Stapedius
    a. Origin – posterior wall of tympanic cavity (pyramidal eminence)
    b. Insertion – stapes
    c. Function – dampens movements of ossicles
    d. Innervation – facial nerve (CN VII; SVE)
  2. Tensor tympani
    a. Origin – cartilaginous part of pharyngotympanic tube
    b. Insertion – malleus
    c. Function – dampens movements of ossicles
    d. Innervation – trigeminal nerve (V3; SVE)
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14
Q

clinical correlation: hyperacusis

A

Paralysis of middle ear muscles can cause hyperacusis (excessive hearing acuteness) due to loss of dampening.

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15
Q

Middle ear: blood supply

A
  1. Inferior tympanic a (from ascending pharyngeal a)
  2. Anterior tympanic a (from maxillary a)
  3. Posterior tympanic a (from stylomastoid a.)
  4. Superior tympanic (from middle meningeal a.)
  5. Artery of pterygoid canal (tubal branches to pharyngotympanic tube).
  6. Venous drainage to ptergyoid plexus
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16
Q

Nerves of the middle ear: CN IX

A

a. Supplies GVA and GVE-P to middle ear and part of auditory tube.
b. Tympanic branch (GVA; GVE-P) – enters middle ear via tympanic canaliculus; forms tympanic plexus on promontory of tympanic cavity.
c. The tympanic plexus provides sensory (GVA) and GVE-P innervation for the middle ear and pharyngotympanic tube.
d. Lesser petrosal nerve reforms from tympanic plexus and exits middle ear via the hiatus for the lesser petrosal nerve (GVE-P). RECALL – this is the source of parasympathetic innervation to the parotid gland.

17
Q

nerves of the middle ear: CN VII

A

a. Supplies motor innervation to stapedius (SVE)
b. Enters internal acoustic meatus, courses along roof of inner ear toward middle ear.
c. Within middle ear, CN VII travels within the facial canal on posterior wall.
d. Chorda tympani is given off right before CN VII exits the middle ear at the stylomastoid foramen; chorda tympani passes between the incus and malleus and then exits the middle ear via the petrotympanic fissure. RECALL – this is the source of SVA to the anterior 2/3rds of the tongue and the source of GVE-P to the submandibular and sublingual glands.

18
Q

Clinical correlation: Otitis media

A

inflammation of middle ear; often due to spread of infection from pharynx via pharyngotympanic tube.

19
Q

Middle Ear Embryology

A
  1. Tympanic cavity and auditory tube form from first pharyngeal pouch.
  2. Malleus, incus and tensor tympani muscle – from first pharyngeal arch.
  3. Stapes and stapedius muscle – from second pharyngeal arch.
  4. CLINICAL CORRELATION: Congenital fixation of stapes can cause deafness.
20
Q

Internal ear

A

A. Housed within the petrous portion of the temporal bone, the internal ear contains the vestibulocochlear organ involved in balance and hearing.

21
Q

Bony labyrinth

A
  1. Bony passages within temporal bone; filled with perilymph.
  2. Cochlea
    a. Shell-shaped bony structure; surrounds cochlear duct.
    b. Modiolus – central, bony core around which cochlea spirals 2.5 times
    c. Spiral ligament – anchors cochlear duct to bony wall of cochlea.
    d. Osseous spiral lamina – anchors cochlear duct to modiolus.
  3. Vestibule
    a. Contains the utricle and saccule.
    b. Vestibular aqueduct – opens near internal acoustic meatus
  4. Semicircular canals.
22
Q

Membranous labyrinth

A
  1. Membranous ducts contained within bony labyrinth; filled with endolymph.
  2. All portions innervated by the CN VIII
  3. Endolymphatic duct
    a. Passes through vestibular aqueduct and ends as endolymphatic sac.
    b. Maintains volume and composition of endolymphatic fluid.
  4. Utricle – responds to changes in horizontal acceleration
  5. Saccule – responds to changes in vertical acceleration
  6. Semicircular ducts (lateral, anterior, posterior) – respond to rotation of head.
  7. Cochlear duct (scala media)
    a. Organ of hearing
    b. Components of cochlear duct
  8. Vestibular membrane – roof (separates cochlear duct from scala vestibuli)
  9. Basilar membrane – floor (separates cochlear duct from scala tympani)
  10. Spiral organ (organ of Corti) – hair cells plus tectorial membrane
23
Q

Vestibulocochlear nerve (CN VIII)

A
  1. Exits brainstem at pontomedullary junction
  2. Passes through internal acoustic meatus to enter inner ear.
  3. Vestibular portion innervates semicircular ducts, utricle, and saccule to carry proprioceptive information (movements of the head) to the brain.
  4. Cochlear portion innervates cochlear duct to carry information about sound to the brainstem.
24
Q

Production of Sound

A
  1. Airways travel down external acoustic meatus causing vibration of tympanic membrane.
  2. Motion of the tympanic membrane causes vibration of the three middle ear ossicles.
  3. Footplate of stapes contacts oval window and causes movement of the fluid in the inner ear.
  4. Movement of fluid in the cochlear duct causes bending of the hair cells imbedded within the spiral organ.
  5. Bending of these hair cells initiates signaling events which ultimately lead to propagation of a nerve impulse along the cochlear portion of CN VIII.
25
Q

Inner Ear Embryology

A
  1. Membranous labyrinth develops from otic placode (ectoderm)→ otic pit → otic vesicle
  2. Bony labyrinth (vestibule, semicircular canals, cochlea) from surrounding mesenchyme.

neuro 2019 Exam 3 (17 decks)

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