Ears - Anatomy and Physiology Flashcards
Into what three parts can the ear be divided?
External
Middle
Inner
What are the 2 functional/structural differing sections of the external ear?
The auricle (or pinna) The external auditory meatus.
What is the auricle/pinna? What is its function?
The auricle is essentially the external, visible ear.
Its function is to capture and transmit sound to the external acoustic meatus.
What is the outer curvature of the ear called?
Helix
What is the name of the curved elevation within the outer curve? What does this divide superiorly to form?
This is the antihelix. It divides to form into 2 cura - the inferoanterior crus and the superoposterior crus.
What is the name of the hollow depression within the middle of the visible ear? What does this continue to??
Concha of Auricle
This is continuous with the external auditory meatus.
What is the function of the concha of the ear?
Acts to direct sound into the external auditory meatus.
Name the slight lips either side of the opening of the external auditory meatus?
Tragus
Antitragus
Generally outline the vasculature of the external portion of the ear.
The main vessels involved are the posterior auricular, superficial temporal and occipital arteries and veins.
Generally outline the innervation of the external portion of the ear.
Cutaneous innervation to the skin of the auricle comes from the greater auricular, lesser occipital and branches of the facial and vagus nerves.
Generally outline the lymphatic drainage of the auricle (pinna)?
Lymphatic drainage of the auricle is to the preauricular, posterior auricular and superficial temporal lymph nodes.
What is the external auditory meatus?
Tube that extends from the deep part of the concha to the tympanic membrane.
What are the walls of the external auditory meatus given their structure by?
Cartilage from the auricle, and bony support from the temporal bone.
In terms of the External Auditory Meatus outline:
- Vasculature
- Innervation
- Lymphatic Drainage?
V
- External part of meatus superficial temporal and posterior auricular.
- Internal part - deep auricular branch of maxillary artery
I
Mandibular and Vagus Nerve
L - Pre and Post auricle and cervical chain
What is the tympanic membrane?
“Ear Drum”
How many layers does the tympanic membrane have?
What are these?
3 layers
- Outer layer - continuous with skin of EAC
- Middle fibrous layer
- Inner layer of resp. epithelium
What is the respiratory layer of the tympanic membrane?
ciliated columnar epithelium with goblet cells
What is otitis media?
An infection of the middle ear which causes pus and fluid to build up. This causes an increase in pressure, and eventually the eardrum ruptures.
What are the causes of eardrum perforation?
Infection
Trauma
Usually will heal itself but if very bad surgery can be indicated.
Where does the middle ear lie?
Middle ear lies within the temporal bone, extends from the tympanic membrane to the lateral wall of the ear.
What is the main function of the middle ear? And how does it do this?
The main function of the middle ear is to transmit vibrations from the tympanic membrane to the inner ear – it does this via the three bones of the ear.
What is the “roof” of the middle ear?
Thin bone from the petrous part of the temporal bone.
What is the “floor” of the middle ear?
(known as the jugular wall)
Thin layer of bone separating meddle ear from Internal Jugular
What is the “lateral wall” of the middle ear?
Tympanic membrane
What is the “medial wall” of the middle ear?
Formed by the lateral wall of the internal ear.
What is the “anterior wall” of the middle ear?
The anterior wall is a thin bony plate with two openings; for the auditory tube and the tensor tympani muscle. It separates the middle ear from the internal carotid artery.
What is the “posterior wall” of the middle ear?
It consists of a bony partition between the tympanic cavity and the mastoid air cells
What are the bones in the middle ear called?
Auditory ossicles.
What are the names of the auditory ossicles?
Malleus, incus and stapes
What is the relation of the auditory ossicles to the external and internal parts of the ear?
Connected in a chain-like manner, linking the tympanic membrane to the oval window of the internal ear.
How does the Malleus attach to the tympanic membrane and the incus?
The malleus has 2 parts: Head and Handle
Attached to the tympanic membrane by the “handle of malleus”.
The head articulates with the incus.
Outline how the incus articulates with the malleus and the stapes?
The incus, consists of a body and two limbs.
The body articulates with the malleus, the short limb attaches to the posterior wall of the middle, and the long limb joins the last of the ossicles; the stapes.
How big is the stapes?
Smallest bone in the body.
What does the stapes do?
It joins the incus to the oval window of the inner ear. It is stirrup-shaped, with a head, two limbs, and a base. The head articulates with the incus, and the base joins the oval window.
What are the 2 muscles within the middle ear?
tensor tympani and stapedius
They contract in response to loud noise, inhibiting the vibrations of the malleus, incus and stapes, and reducing the transmission of sound to the inner ear. This action is known as the acoustic reflex.
Where does the tensor tympani originate, attach and is innervated by?
Originates from the auditory tube and attaches to the handle of malleus, pulling it medially when contracting.
Where does the stapedius muscle attach and what innervates it?
Stapedius muscle attaches to the stapes, and is innervated by the facial nerve.
What is the auditory tube? Whats its function?
The auditory tube (eustachian tube) is a cartilaginous and bony tube that connects the middle ear to the nasopharynx.
It acts to equalise the pressure of the middle ear to that of the external auditory meatus.
What is the major nerve supplying the middle ear?
Facial nerve (CN VII)
How many segments is the facial nerve in the middle ear split? What are they?
Intracranial
Meatal segment (internal auditory meatus)
Labyrinthine segment
Tympanic segment (Fallopian tube. 10% of which are dehiscent. i.e within mucosa)
Mastoid segment
Extratemporal segment
What is Cholestaetoma?
Keratinized squamous epithelium in the wrong place (middle ear)
Can be congenital or acquired
Cause problems because they grow and are destructive
What are the 2 functions of the inner ear?
Conversion of mechanical signals from the middle ear into electrical signals which can transfer signals to the auditory pathway in the brain.
Maintain balance by detecting position and motion.
Where is the inner ear located?
Within the petrous part of the temporal bone.
What are the 2 main components of the inner ear?
The bony labyrinth.
The membranous labyrinth.
What is the bony labyrinth of the inner ear?
Series of bony cavities within the petrous part of the temporal bone.
Composed of the cochlea, vestibule and three semicircular canals.
What are all the structures of the bony labyrinth lined with? and contain?
inner ear
Lined internally with periosteum and contain a fluid called perilymph.
What is the membranous labyrinth of the inner ear?
Lies within the bony labyrinth.
It consists of the cochlear duct, semicircular ducts, utricle and the saccule. The membranous labyrinth is filled with fluid called endolymph.
What is the vestibule of the bony labyrinth?
Central part of the bony labyrinth. Separated from middle ear by the oval window.
Two parts of the membranous labyrinth; the saccule and utricle, are located within the vestibule.
What is the cochlea?
Houses the cochlea duct of the membranous labyrinth – the auditory part of the inner ear.
What is the name of the central portion of bone the cochlea twists around?
Modiolus
What are the semicircular canals in the inner ear? Where are they found?
3 canals anterior, lateral and posterior.
They contain the semicircular ducts, which are responsible for balance (along with the utricle and saccule).
The canals are situated superoposterior to the vestibule, at right angles to each other. They have a swelling at one end, known as the ampulla.
Where is the cochlear duct found?
within the bony scaffolding of the cochlea
The presence of the cochlear duct creates what?
The presence of the duct creates two canals above and below it – the scala vestibuli and scala tympani respectively.
What is the Organ of Corti?
The epithelial cells of hearing.,
How do the semicircular ducts of the inner ear function in terms of balance?
Upon movement of the head, the flow of endolymph within the ducts changes speed and/or direction. Sensory receptors in the ampullae of the semicircular canals detect this change, and send signals to the brain, allowing for the processing of balance.
What is the arterial supply of the bony labyrinth of the inner ear?
Anterior tympanic branch (from maxillary artery).
Petrosal branch (from middle meningeal artery).
Stylomastoid branch (from posterior auricular artery).
What is the arterial supply of the membranous labyrinth?
Supplied by the labyrinthine artery, a branch of the inferior cerebellar artery.
It divides into three branches:
Cochlear branch – supplies the cochlear duct. Vestibular branches (x2) – supply the vestibular apparatus
What is the venous drainage of the inner ear?
Through the labyrinthine vein, which empties into the sigmoid sinus or inferior petrosal sinus.
Innervation of the inner ear?
Vestibulocochlear nerve (CN VIII)
divides into the vestibular nerve (responsible for balance) and the cochlear nerve (responsible for hearing):
Generally outline how hearing occurs.
Function of middle ear is transduce vibration into nervous impulses
Foot of stapes vibrates in oval window
Causes pressure wave through fluid in cochlear
This is detected by hair cells in organ of corti
Transmitted to brainstem (junction of pons and medulla) by CN VIII
Generally outline balance within the ear.
Semicircular canals are responsible for detecting head rotation
- Vestibulo-ocular relfex – what makes you able to fix your vision on an object even when your head is moving
Saccule – detects linear acceleration in vertical plane
Utricle – detects linear acceleration in horizontal plane
What nerve gives sensation to the middle ear?
Tympanic branch of glossopharyngeal nerve (CN IX) AKA Jacobsons nerve.
What nerve gives sensation to the posterior half of EAC?
Auricular branch of vagus nerve (CN X) AKA Arnolds nerve
What nerve innervates the anterior EAC?
Facial nerve
What nerve innnervates the pinna?
Mandibular branch of trigeminal nerve (CN V3)
What is the importnace of shared innervation clinically?
Otalgia (ear pain) is a worrying sign if there is no obvious ear pathology.
Cause can be cancer of the head and neck
