outer ear Flashcards
structures of the outer ear
pinna (auricle), external auditory meatus (canal), and ends at the tympanic membrane
physiological aspect of the outer ear
conductive mechanism
how is the skin of the ear related to the skin on our body
skin is continuous with the skin covering the body
pinna
outside part of the ear (auricle)
lobule
lobe of ear
tragus
nub that stands out in front of canal
intertragal notch
notch under the tragus
antitragus
back side of ear, opposite of intertragal notch
concha
area within ear before going into the canal
cavum
“cave” going into the canal
cymba
top tuck above the concha
helix
back rim that goes around the pinna
crus of helix
arm of the helix
antihelix
little rim inside of the concha
crural of antihelix
two smaller arm reaching out to the helix on the top part of the ear
triangular fossa
in between crural of antihelix
scaphoid fossa
between helix and antihelix
tubercle
little bump on helix
-not very prominent for some people
nervous supply to outer ear
-great auricular nerve (C2 and C3)
-lesser occipital nerve (C2, C3)
external auditory canal (external auditory meatus)
tube like channel of the external ear extending from the pinna to the tympanic membrane
-more oval shaped
average length of the external ear canal
2.5 cm length
-25 mm
average length of the canal in females
28 mm
average canal length in males
30 mm
outer half of the external auditory canal
supported by cartilage, thin skin with dermal papillae
-cartilaginous
inner half of the external auditory canal
supported by bone, small hairs and glands along upper wall only
-bony
how many curves does the canal have
2
isthmus
narrowest portion of the canal
fissures of santorini
where cartilage is ending and bone begins
-potential infection path
how is the fissure of santorini a potential pathway for infection
because the cartilage is not continuous
physiology of the external auditory canal
protective function
-achieved by anatomy (angled direction)
what part of the external ear canal is longer?
the floor/inferior wall in longer than the ceiling/superior wall
cerumen
ear wax
how is cerumen produced?
ceruminous glands
-modified apocrine sweat glands with combination of sebaceous glands
what is epithelial migration
within a normal ear canal, the surface of the skin moves laterally from the medial end to the lateral end
-purpose is to keep the canal free of debris
what is the purpose of cerumen
lubricates, protects, and provides moisture
-natural
-antibacterial and anti-fungal properties
biochemistry of cerumen
mixture of lipids, proteins, aminos acids, and mineral ions
properties of canal hairs
-short hair
-medial hairs lay at a angle
-lateral hairs are more upright
cranial nerve innervation of the outer ear
trigeminal, facial, and vagus (5, 7, 10)
what branch of the trigeminal nerve
auriculotemporal branch of mandibular division of CN 5
what branch of the facial nerve
posterior auricular branch of CN 7
what branch of the vagus nerve
auricular branch of CN 10 (arnold’s nerve)
vagus reflex
may be evoked during insertion of an otoblock used in making earmold impressions, cerumen management, and rarely with hearing aids
-arnold’s nerve or ear-cough reflex
what can the vagus reflex cause
cough reflex, sneezing, gagging, vomiting, syncope, cardiac depression, dizziness
non-acoustic occlusion effect
making a plugged up feeling
-nerve and tissue are swelling up which makes this feeling
trigeminal reflex
can cause excessive vascularization and thickening of the TM during otoscopy, otoblock insertion, and during hearing aid wearing
-red reflex
lymphatic reflex
slow reflex which may result from over wearing of hearing aids during the adaptation period
-might need to slow into full time hearing aid wearing
sound pressure gain
external ear can be considered a passive amplifier that increases the sound pressure level at the eardrum compared to the SPL in the air outside the head
ear canal resonance
one lumped resonance based on sound pressure at various areas within the ear
how does the external auditory canal act as a resonator
it is a closed (on one end) tube resonator
fundamental frequency for the resonance
will be 1/4 of the wavelength when it is closed at one end
-what length it will resonant the best at
effects of the ear canal and resonance
the resonant frequency is based on the tube length
-considered to be a tube that is closed on one end
-average ear canal has a resonant frequency of around 3000 Hz
effects of the ear canal and pinna combined on resonance
causes a slightly different sound pressure curve
-concha serves as a end correction and lowers the resonant frequency to around 2700 (17 dB) Hz
-produces a composite curve with two peaks (2700 and 5000 Hz)
inverse square law
as the energy spreads out from the source, it will cover more area and each block will be 1/4th the intensity
-larger receiver will pick up more energy
more medial canal hairs lie ______ , more lateral canal hairs lie _______
flat, oblique
what do the bends in the canal do
reduce occlusion effects
