In an attempt to understand the functional anatomy of the ear, it is best to study it in three separate units, The Outer ear, The middle ear and The inner ear,
The outer ear consists of the auditory apparatus that conducts sound waves, The Middle ear is a boxlike region that transmits these sound waves into the inner ear,
The Inner ear is functionally the most important, it contains the coclea, and the semicircular canals
The coclea transmits the sound wave into nerve impulses and the semicircular canal maintains balance
The major components of the outer ear include the auricle, and the external auditory meatus, ( acoustic Meatus), The auricle is the extension of cartilage that we called the ear when we were 4 or 5
The Acoustic meatus is the internal canal that ends at the tympanic membrane ( Ear Drum)
The are various components of the Auricle, which should be located using an anatomy atlas.
Blood supply to these regions and the external auditory meatus is via the:
1. Posterior Auricular Artery
2. Maxillary Artery
3. Temoral and superficial temporal arteries
The Nerve supply to the Outer Ear is by the auricotemporal nerve ( V-3 Branch)
And the Auricular Nerve ( Branch of the Vagus)
These two nerves also inervate the Tympanic membrane as well
* Re-call Sensory to the Face is predominantly via trigeminal nerve aka (CN-V)
Located in the Petrous part of the temporal bone, it is an extremely difficult structure to visualize.
As I mentioned before, the best way to understand the middle ear is by envisioning it to be an empty box.
If you have followed correctly you should be able to deduce the lateral border of the Middle ear….
Ans : The Tympanic Membrane
The medial Border consists of three structures
- The Oval window
- The Round Window contains the second
- The Promontory which represents the first turn
of the cochlea.Along the Anterior Border aka the front of the box is the Carotid wall where the carotid artery
lies, (the Carotid wall separates the artery from the middle ear space).
The Posterior Border aka the back of the box lies the Mastoid wall , The floor of the box is the
Jugular wall where the jugular vein lies.
The roof is the tegmen tympani bone ( a component of the middle Cranial Fossa ) See Cranial
The Lateral Wall
The Tympanic Membrane is a pearl gray structure to which the mallus is attached. The
structure is divided into four quadrants, Anterior Inferior, Posterior Inferior.
The Anterior Inferior Region reflects light thus it is referred to as the cone of light.
The Corda Timpani crosses the manubrium of the Mallus.
The epitympanic recess is the space between the mallus and the Incus , and is continuous with the mastoid air cells posterior.
The Medial Wall
The facial nerve transverses the facial canal and enters the posterior wall where it gives of several branches. ( It lies above the oval window ) and exits the Middle ear through the Stylomastoid foramen.
The venous plexus is formed from branches of the tympanic membrane, The lesser petrosal is one such branch that exits through the hiatus for the lesser petrousal And it will inervate the parotid gland.
Has an opening which leads into the eustacian tube and this provides a connection between the ear and the nasopharynx. The tensor tympani which is inervated by V-3 lies in this area.
The stapedus muscle comes of the posterior wall which contains the facial nerve The nerves that come of the facial nerve in this region are the Nerve to stapidus and the chorda tympani.
Contents of the Middle Cavity
There are three important bony prominences worth noting
1. The Incus
2. The Mallus
3. The Stapes
These help convey sound from the tympanic Membrane to the oval window. The Inner mucous lining of the Middle ear is inervated by Glosopyrangial where as the outer lining (external ear is innervated by branches of trigeminal.
The Inner Ear
The inner ear is composed of two important components:
1. The Bony Labyrinth
2. The Membranous Labyrinth
With in the inner ear lies the Vestibular System made up of the semicervular canals and the Auditory System, ( The Cochlea).
The membranous Labyrinth is separated from the bony labyrinth by the a fluid called perilymph.