NB 29+30 Flashcards
innervation of the auricle
posterior 2/3 = great auricular (C2/C3) and lesser occipital N (C2)
anterior 1/3 = Auriculotemporal nerve (V3)
development of the auricle
The ear develops from 6 auricular hillocks
3 from the 1st arch and 3 from the 2nd arch mesenchyme tissue
malformation can lead to auricular sinuses and cysts
Pre-auricular sinus
due to incomplete fusion of the primitive tubercles that form the pinna
Preauricular pits
Auricular sinuses/pits are usually present anterior to the auricle and considered remnants of the 1st pharyngeal groove.
common! May indicate other congenital defects
External acoustic meatus
lateral 1/3 of canal is cartilaginous
medical 2/3 is bony and part of the tympanic portion of temporal bone
innervated by the Auriculotemporal nerve (V3)
a small area is innervated by CN X
innervation of the tympanic membrane
external surface auriculotemporal nerve (V3) except for small area by CN VII and CN X
internal surface is by tympanic plexus (CN IX)
innervation of the middle ear
glossopharyngeal nerve via the tympanic plexus
development of the middle ear
Develops from the distal expanded part of the tubotympanic recess arising from the 1st pharyngeal pouch
where do the auditory ossicles develop from
malleus and incus develop from the 1st arch
stapes from the 2nd arch
tensor tympani is the first arch
stapedius is from the second arch
development of external ear
Surface ectoderm grows & forms a solid meatal plug which undergoes canalization to form the external auditory meatus
development of the tympanic membrane
develops from the 1st pharyngeal membrane
it is derived from all three germ layers
chorda tympani nerve
sensory fibers for taste from anterior 2/3 of tongue
parasympathetic (preganglionic) innervation for submandibular and sublingual glands
disruption of ossicular chain
conductive hearing loss
clinical importance of the stapes
otosclerosis
clinical importance of chorda tympani N
reduction of salivation if damaged
middle ear boundaries
roof (tegmen tympani) - separates cavity from middle cranial fossa
medial wall - separates cavity from middle ear
anterior wall - separates cavity from carotid canal
floor: base of skull near jugular foramen
lateral wall: mainly tympanic membrane
posterior wall - separates cavity from mastoid air
cells
innervation of the inner ear
CN VIII
vestibular nerve - balance
cochlear nerve - hearing
development of the inner ear
The otic vesicle, derived from the ectoderm, will give rise to the membranous labyrinth
The cartilaginous otic capsule undergoes ossification to form the bony labyrinth
Atresia of EAM
absent external acoustic meatus
failure of the central cells of the meatal plug to canalize
middle ear amplification
pressure = force / area
decrease area
increase force
what two muscles limit excessive pressure in the middle ear
Contraction of m. tensor tympani and m. stapedius
occurs in response to high intensity sound – attenuation reflex
restricts the movement of the tympanic membrane and makes the ossicles more rigid
does not protect against sudden loud noises
outer hair cells and inner hair cells
outer = signal amplification ( K influx / depolarized)
these cells expand when hyperpolarized and compress when depolarized
inner = majority of signal transduction (no K influx / hyperpolarize)
lesions to lead to unilateral hearing loss
cochlear nuclei
ear
CN VIII
Area 41 and 42
primary auditory cortex
Vestibular Schwannoma
a benign tumor originating from the Schwann cells of the vestibular division of CN VIII
this tumor compresses the nerve within the internal auditory meatus
symptoms are sensorineural hearing loss and tinnitus
Meniere’s Disease
repeated episodes of vertigo, can have tinnitus and progressive sensorineural hearing loss
due to distortion of the membranous labyrinth that results in an over production of endolymph
Weber’s test
testing auditory functioning
normal:
hear the the tuning fork the same on each side
abnormal:
the sound is louder on one side compared to the other
how to interpret abnormal weber’s test
In sensorineural hearing loss:
The sound lateralizes to the unaffected side
Conductive hearing loss:
The sound will lateralize to the affected side
lateralize = louder
Rinne’s test
- bone conduction
the stem of the turning fork is put on mastoid process
(bone to inner ear)
patient must say when they no longer hear it - air conduction
bring the tuning fork to the ear
(do you hear sound again? when dont you hear it)
normal and abnormal Rinne’s test
normal:
air conduction sound should be better than bone conduction AC > BC
abnormal:
BC > AC
conductive hearing loss
AC > BC
but times of hearing vibration are different
Sensorineural hearing loss
AC = BC = 0
total deafness
Weber’s test lateralizes to the left
Rinne’s test is BC > AC
conductive hearing loss on the left
Weber’s test lateralizes to the left
Rinne’s test AC > BC ( but reduced times )
sensorineural hearing loss on the right
