What is the blood supply to the ear?
Posterior auricular and superficial temporal arteries off the external carotid
In the substance of which bone is the ear embedded?
The temporal bone
What is the function of the auricle?
Collect sound and funnel into the external auditory meatus
The external auditory meatus is lined by skin. What does it secrete? What is the function of this secretion?
Cerumen It protects the delicate skin of the eam
What forms wax?
Cerumen and discarded cells of the skin
How do we position the auricle to examine the ear and why?
The course of the ear is sigmoid-shape so the auricle is pulled upwards and backwards during examination
What are the three auditory ossicles of the middle ear? What is their function?
Malleus, incus and stapes Transit the vibrations from the tympanic membrane to the inner ear. They amplify and concentrate sound energy from the ear drum to the oval window
What are the anterior relations of the middle ear cavity?
Communicates with the nasopharynx via the Eustachian tube
What are the posterior relations of the middle ear cavity?
Communicates with the mastoid air cells via the epitympanic recess and mastoid Antrum
How does the ossicles connect the external ear to the inner ear?
The handle of the malleus is attached to the tympanic membrane.
The body of the malleus articulates with the incus
The incus articulates with the stapes
The stapes articulates with the bony labyrinth of the internal ear at the oval window
How can the facial nerve be affected by an ear infection?
The facial nerve lies in the facial canal, which is separated from the middle ear cavity by a thin bony partition, therefore due to the close proximity a middle ear infection can cause a lesion of the facial nerve
How is the middle ear cavity divided in to two further cavities?
Separated into the tympanic cavity and epitympanic recess by a line from the top of the tympanic membrane to the medial wall
What is the clinical importance of the Eustachian tube?
Spread of respiratory infections The Eustachian tube is usually closed, when swallowing it is pulled open by the pull of the attached palatine muscles
What are the two muscles associated with the auditory ossicles? How are they innervated?
Tensor tympani - CNV3 Stapedius - nerve to stapedius off CN7
What is the function of the tensor tympani?
It attaches to the handle of the malleus It pulls the handle medially This tenses the tympanic membrane and reduces the amplifications of its oscillations. It prevents damage to the inner ear when exposed to large sounds
What is the function of the Stapedius?
Pulls the stapes posteriorly to prevent excessive movement of the stapes and reduces the oscillatory range
What is the sensory innervation to the tympanic membrane?
Internal surface: CN9 (glossopharnygeal)
External surface: auriculotemporal (off CNV3) and the auricular branch of the vagus (CNX)
What is meant by Arnold's cough reflex?
Stimulation of the auricular branch of the vagus nerve causes a cough reflex and some people even vomit. E.g. Insertion of a cotton bud or foreign body in the ear
Afferents: auricular branch of the vagus nerve
Efferents: superior laryngeal branch of the vagus and the phrenic nerve
What is the structure of the external auditory canal?
Lateral 1/3 is cartilage Medial 2/3 is bone
The inner ear is also known as the labyrinth. What are the two parts of the labyrinth? How are they separated from each other?
A membranous labyrinth is contained within a bony labyrinth The membranous labyrinth contains fluid called endolymph A fluid called peri lymph separates the bony labyrinth from the membranous labyrinth
We can divide the inner ear into the vestibule and the cochlea. What is the structure of the vestibule?
Contains the utricle and saccule, they have receptors that respond to rotational acceleration and the static pull of gravity. There are three semicircular canals that communicate with the vestibule and they are perpendicular to each other. They have receptors that respond to rotational acceleration in three different planes
We can divide the inner ear into the vestibule and the cochlea. What is the structure of the cochlea?
Scala vestibuli, scala media and scala tympani Scala vestibuli casues vibration of scala media Spiral organ of Corti - strip of epithelial cells that convert the auditory signals into an action potential
What is the sensory nerve supply to the auricle of the external ear and the tympanic membrane?
Outer aspect of the auricle is supplied by the auriculotemporal nerve (CNV3) and the greater auricular nerve (C2 and C3 of the cervical plexus)
Name three branches from the facial nerve given off in the Petrous temporal bone and what is their functional significance?
Greater petrosal nerve - contains preganglionic parasympathetic fibres that pass through the pterygopalatine ganglion to innervate the lacrimal glands and glands of the nose Chorda tympani - contains special taste fibres to the anterior 2/3 of the tongue and paras to the sublingual and submandibular glands Nerve to the stapedius - helps protect the inner ear from loud noises
What forms the roof of the middle ear cavity?
Petrous part of the temporal bone (separates the middle ear from the middle cranial fossa)
What forms the floor of the middle ear cavity?
Jugular wall (a thin layer of bone to separate the middle ear from the internal jugular vein)
What forms the medial wall of the middle ear cavity?
Lateral wall of the inner ear. It has the oval and round windows and the prominence of the facial canal
What forms the lateral wall of the middle ear cavity?
What are the layers of the tympanic membrane?
Outer: keratinised stratified squamous
Middle: fibrous layer
Inner: Pseudostratified columnar
What are the different parts of the tympanic membrane?
What are the different parts of the outer ear?
What is meant by the cone of light?
Seen when shining a light on to the tympanic membrane
it appears in the anterior inferior quadrant