Transcript Anatomy and physiology of the outer ear

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Extrinsic
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Connect pinna to skull & scalp
Supplied by facial nerve
Very little voluntary control in humans
But auditory stimuli may evoke responses => some
clinical value (electromyography)
Intrinsic
◦ Connect different parts of pinna
◦ Supplied by facial nerve
◦ Very occasionally humans can activate
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EAM has complex sensory innervation derived
from cranial nerves V (trigiminal), VII (facial),
IX (glossopharyngeal) and X (vagus)
Mechanical stimulation (e.g. in wax removal,
taking impressions) can cause:
◦ Coughing, altered cardiac function, fainting
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Eardrum
 Concave, disk like structure
 Viewed with the structures of the outer ear
 It is a boundary between the OE and ME
 The tymapanic membrane is composed of three
layers
1. Outer layer made of skin (cutaneous) that is
stretched to the osseous meatus
2. The middle layer made of tough fibrous
connective tissue which contributes to the
membranes ability to vibrate with impinging
sound waves
3. Inner layer lined with mucous membrane
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The total area of the TM is about 63.3 mm2
It is extremely thin averaging about 0.07 mm
Efficient vibrating surface
Rich in blood supply
The malleus (largest bone of the ME) is
embedded in the fibrous portion of the TM
(_______ layer)
The handle of the malleus runs 11 o'clock in the
left ear
The tip of the malleus ends in the approximate
centre of the TM and angles downward and
backward.
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Umbo is the point of greatest retraction, at the
centre of the TM
The TM is observed by directing light from a
device called an otoscope that contains a
magnifying lens
The TM is semi-transparanet thus the light
allows some of the ME structures to become
visible, the light rays directed against the TM are
reflected and refracted producing a light reflex
The light reflex is a cone shaped, gives indication
of the ear tested (same direction of the tested
ear)
The tympanic annulus is a ring of tissues that
hold the TM in position at the end of EAC
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Pars tensa – most of surface
◦ Taut
◦ Made up of four layers of tissue
 Most lateral – thin layer of skin (continuous with EAM)
 Then two dense fibrous layers – radial & circular fibres
(in that order)
 Most medial – mucous layer (continuous with mucous
membrane of middle ear)
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Pars flaccida – superior region
◦ Thin, lax
◦ Only two layers of tissue (lacks fibrous layers)
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Manubrium of malleus is usually visible under
otoscopy
◦ Tip is at umbo
◦ Runs to eleven-o-clock position in left ear
◦ (‘Cone of light under otoscopy –
___________________________ region)
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It is the first mobile link in the chain of
auditory events, and it reproduces the same
spectrum of sounds that enter the EAC
Movement of the TM causes identical
vibration of the malleus
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28th day of conception the human embryo
bulges begin to appear on either side of the
tissue that will develop into the head and
neck, pharyngeal arches
6 arches separated by grooves or clefts
Significant information is only available about
the first three
Mandibular arch
Hyoid arch
Glossopharengeal arch
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These arches are known to have three layers
1. Ectoderm- outer layer
2. Endoderm- inner layer
3. Mesoderm- inner core
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Each arch contains
Artery
Mesoderm
Muscle
Cartilage
Nerve -ectoderm
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The auricle develops from the first two
pharyngeal arches
The tragus forms from the first arch
Helix and antitragus from the second arch
2nd foetal month, the development of the
auricle
The EAC forms from the first pharyngeal
groove and is very shallow until after birth
By the fourth gestational week a primitive
meatus is formed, by the 8th week solid core
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28th gestational week the solid core canalizes
(form tube), although the entire osseous
meatus is not complete until the time of
puberty
Pneumatisation or the formation of air
cavities in the temporal bone surrounding the
EAC begins at 35th foetal week, accelerated at
the time of birth
By the third foetal month the TM annulus is
formed
The formation of the TM begins by the start
of the second embryonic month
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Congenital
– Microtia (small ear size)
- Prominent auricle that stand away from the head
- Anotia (absent auricle)
Acquired
-accidents
- Cancer
- Burns
- Trauma
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Congenital
Atresia (the absence of the EAC)
Stenosis (narrowing of the ear canal)
Acquired
Burns
Trauma
Collapsed ear canal (narrowing or closure of the canal
caused by pressure of compressing the pinna against
the side of the head
Foreign bodies in the EAC
Ear wax in the EAC
External otitis
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Perforation in the TM
Grommet in the TM
Scarred TM
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