Ear Flashcards
External Acoustic Meatus
Tube that extends from the deep part of the concha to the tympanic membrane.
Tympanic Membrane
It is a connective tissue structure, at the end of the external acoustic meatus, covered with skin on the outside and a mucous membrane on the inside.
Walls of the external acoustic meatus
External 1/3 are formed by cartilage, whereas the inner 2/3 are formed by the temporal bone.
What attaches to the tympanic membrane?
Handle of malleus attaches to the tympanic membrane, at a point called the umbo of tympanic membrane.
What innervates the skin of the auricle?
Greater auricular nerve (branch of the cervical plexus) Lesser occipital nerve (branch of the cervical plexus)
What innervates the skin of the auricle and external auditory meatus?
Auriculotemporal nerve (branch of the mandibular V3 nerve)
What innervates the deeper aspect of the auricle and external auditory meatus?
Branches of the facial and vagus nerves
Auditory ossicles
Malleus, incus and stapes
What does each ossicle join to?
Malleus (tympanic membrane to incus)
Incus (malleus to stapes)
Stapes (incus to oval window)
What are the two muscles which serve a protective function in the middle ear?
Tensor tympani and stapedius.
What is the function of the middle ear muscles?
They contract in response to loud noise (own voice), 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 do the middle ear muscles attach?
Tensor tympani originates from the auditory tube and attaches to the handle of malleus, pulling it medially when contracting.
Stapedius is attached to the stapes
What innervates the middle ear muscles?
Tensor tympani is innervated by the tensor tympani nerve, a branch of the mandibular nerve V3.
Stapedius is innervated by the facial nerve.
What is hyperacusis associated with and why?
Associated with facial nerve palsies which cause loss of the ear’s protective stapedial reflex.
What is the eustachian tube?
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.
Bony labyrinth
Consists of a series of bony cavities within the petrous part of the temporal bone. It is composed of the cochlea, vestibule and three semi-circular canals.
Vestibule
Central part of the bony labyrinth.
It is separated from the middle ear by the oval window, and communicates anteriorly with the cochlea and posteriorly with the semi-circular canals.
Cochlea
Auditory part of the inner ear.
It spirals forming a central modiolus, branches from the cochlear portion of the vestibulocochlear (VIII) nerve are found at the base of the modiolus.
Extending outwards from the modiolus is a ledge of bone known as spiral lamina.
Semi-circular Canals
There are three semi-circular canals: anterior, lateral and posterior. They contain the semi-circular ducts, which are responsible for balance (along with the utricle and saccule).
What parts of the membranous labyrinth are located in the vestibule?
Two parts of the membranous labyrinth; the saccule and utricle, are located within the vestibule
Membranous labyrinth
Lies within the bony labyrinth. It consists of the cochlear duct, semi-circular ducts, utricle and the saccule. The membranous labyrinth is filled with fluid called endolymph.
Cochlea duct
The presence of the cochlear duct (scala media) creates two perilymph-filled chambers above and below
Scala vestibuli: Located superiorly to the cochlear duct. As its name suggests, it is continuous with the vestibule.
Scala tympani: Located inferiorly to the cochlear duct. It terminates at the round window.
Semi-circular Ducts
The semi-circular ducts are located within the semi-circular canals, and share their orientation.
Upon movement of the head, endolymph flows within ducts and changes speed and direction, sensory receptors in the ampullae detect this and signal to brain
Saccule and Utricle
The saccule and utricle are two membranous sacs located in the vestibule.
They are organs of balance which detect movement or acceleration of the head in the vertical and horizontal planes, respectively.
Endolymph drains from the saccule and utricle into the endolymphatic duct.
Vestibular nerve passage
Enlarges to form the vestibular ganglion, which then splits into superior and inferior parts to supply the utricle, saccule and three semi-circular ducts.
Cochlear nerve passage
Enters at the base of the modiolus and its branches pass through the lamina to supply the receptors of the Organ of Corti.
