Outer and middle ear Introduction
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91 Terms
What does Anatomy mean?
structure of the body
What does Physiology mean?
how the body functions
What does Pathophysiology mean?
how body functions in the diseased state
What direction is Medial?
Middle
What direction is Posterior?
Back
What direction is Anterior?
Front
What direction is Superior?
top
what direction is Inferior?
bottom
What does “Squamous” mean and what does it form?
“Scale-like thin.” The flat portion forms part of the side of the skull.
What does “Petrous” mean and what does it surround and protect?
“Like rock, very hard.” It is the dense part that surrounds and protects the inner ear.
What is the pinna made of?
Elastic fibrocartilage, covered by skin.
What is the exception to the pinna’s structure?
The lobule, which is made of fibrous and adipose tissue (both loose connective tissues), not cartilage.
What are the intrinsic muscles of the pinna and what do they connect?
Intrinsic muscles connect different parts of the pinna.
What are the extrinsic muscles of the pinna and what do they connect?
Extrinsic muscles connect the pinna to the skull and scalp.
Which nerve supplies the muscles of the pinna?
The facial nerve (cranial nerve VII).
How much voluntary control do humans have over the muscles of the pinna?
Very little voluntary control.
What is another name for the ear canal?
The external auditory meatus (EAM).
Where does the external auditory meatus (EAM) run?
From the concha to the eardrum.
What is the average length of the external auditory meatus in adults?
About 2.5 cm.
What is the average diameter of the external auditory meatus at its entrance?
About 0.7 cm.
What is the mean horizontal diameter of the adult external auditory meatus?
About 0.65 cm.
What is the mean vertical diameter of the adult external auditory meatus?
About 0.9 cm.
What is the cross-sectional shape of the external auditory meatus?
Oval (because vertical diameter is larger than horizontal).
How many bends does the external auditory meatus have along its length?
Two bends.
What is the overall shape of the external auditory meatus?
Slight S-shape (see Gelfand for details).
What lines the external auditory meatus (EAM)?
Tight fitting skin.
What portion of the EAM is cartilaginous?
The outer third.
How does the skin of the cartilaginous portion of the EAM compare to the bony portion?
It is thicker.
What structures are found in the cartilaginous portion of the EAM?
Numerous hair follicles, ceruminous glands, and sebaceous glands.
What do the ceruminous and sebaceous glands in the EAM secrete?
Cerumen (a mixture of wax and oil).
What portion of the EAM is osseous (bony)?
The inner two-thirds.
How many follicles and glands are in the osseous portion of the EAM compared to the cartilaginous portion?
Fewer, but they are still present on the posterior and superior walls.
what is the EAM in children like?
EAM is relatively straight & cartilaginous
What is cerumen composed of?
A mixture of wax and oil.
Where is cerumen mainly produced in the ear canal?
In the cartilaginous portion of the external auditory meatus.
What protective properties does cerumen have?
Slight antifungal and antibacterial properties.
How does cerumen help remove dead skin and debris?
It migrates outward, carrying dead skin and debris with it.
How does cerumen help prevent the ingress of debris?
By working in combination with hairs in the ear canal.
What problems can result from over-production or accumulation of cerumen?
It may completely occlude (block) the meatus.
What lines the wall of the external auditory meatus (EAM)?
Epidermis (a layer of skin).
With which structure is the epidermis of the EAM continuous?
The tympanic membrane (TM).
How does the skin of the EAM grow?
Outwards from the tympanic membrane and migrates along the ear canal, carrying cerumen and debris.
What aids the migration of cerumen in the ear canal?
Jaw movement.
How many different cranial nerves innervate the EAM?
Four.
What symptoms can occur if the inner part of the EAM is touched (e.g., during wax removal)?
Coughing, altered cardiac function, or fainting.
How is the tympanic membrane (TM) positioned in the ear canal?
It tilts laterally and is set obliquely.
Which walls of the external auditory meatus are longer, affecting the tilt of the TM?
The inferior and anterior walls are longer than the superior and posterior walls.
What structure attaches the TM around its circumference?
A fibrocartilaginous ring called the annulus.
What is the approximate diameter of the TM?
About 1 cm (slightly elliptical).
What is the overall shape of the TM when viewed laterally?
Concave.
What is the most medial point of the TM called?
The umbo.
What are the physical properties of the TM in terms of thickness and appearance?
It is thin, translucent, and has an average thickness of less than 0.1 mm.
What are two other names for the Middle Ear Cavity?
“Tympanum” or “tympanic cavity.”
What is the Middle Ear Cavity?
A narrow air-filled cavity between the outer and inner ear.
Where is the Middle Ear Cavity located?
Within the petrous portion of the temporal bone of the skull.
How is the Middle Ear Cavity described?
An irregular, laterally compressed space, sometimes described as a biconcave lens.
Where is the Middle Ear Cavity the narrowest and what is its width there?
At the umbo, about 2 mm across.
What is the width of the Middle Ear Cavity at the top and bottom?
About 6 mm at the top and bottom.
What structures are found in the tympanum (middle ear cavity)?
Middle-ear ossicles, middle-ear muscles (tensor tympani, stapedius muscle), oval window, round window, cochlear promontory, and the Eustachian tube.
What are the middle-ear muscles?
Tensor tympani and stapedius muscle.
Where does the oval window lead?
Into the scala vestibuli of the cochlea.
Where does the round window lead?
Into the scala tympani of the cochlea.
What creates the cochlear promontory (prominence anterior to the windows)?
The first turn of the cochlea.
What are the alternative names for the Eustachian tube?
Pharyngotympanic tube or auditory tube.
What is another name for the malleus?
Hammer.
Where is the malleus attached?
To the tympanic membrane (along the manubrium), ending in the umbo.
Where is the head of the malleus located?
In the epitympanic recess.
Which muscle is connected to the malleus?
The tensor tympani tendon.
What is another name for the incus?
Anvil.
What are the main parts of the incus?
Body, long process, and short process.
With what does the body of the incus articulate?
The malleus.
What kind of joint does the incus form with the head of the stapes?
A ball-and-socket joint.
What is another name for the stapes?
Stirrup.
What are the parts of the stapes?
Head, neck, crura (“legs”), and footplate.
To what is the footplate of the stapes attached, and by what structure?
Attached to the oval window by the annular ligament.
What connects the neck of the stapes to the stapedius muscle?
The stapedius tendon.
What does the Eustachian tube connect?
The middle ear cavity to the nasopharynx.
How long is the Eustachian tube?
About 2.5 cm.
What lines the Eustachian tube?
A mucous membrane.
What portion of the Eustachian tube is bony?
The lateral third (towards the middle ear).
What portion of the Eustachian tube is cartilaginous?
The medial two-thirds.
Is the Eustachian tube normally open or closed?
Normally closed.
How does the Eustachian tube open?
By reflex action of the tensor veli palatini muscle (probably combined with the tensor tympani).
Which cranial nerve innervates the muscles that open the Eustachian tube?
The trigeminal nerve (cranial nerve V).
When does the Eustachian tube typically open?
During swallowing, yawning, and sneezing.
What is the main function of the Eustachian tube?
Equalisation of pressure in the middle ear cavity with outside pressure.
In what situations is the Eustachian tube important for pressure equalisation?
Air flight, changes in altitude, or changes in ambient atmospheric pressure (weather).
What happens if the Eustachian tube becomes blocked?
A pressure difference develops across the tympanic membrane (TM).
What does negative pressure in the middle ear cavity cause?
Secretions of fluid from the blood and middle ear tissues.
How does fluid in the middle ear affect hearing?
It further impairs sound transmission.
Besides equalisation of pressure, what are two other functions of the Eustachian tube?
Drainage and ventilation of the middle ear cavity.