Functions of the inner ear?
Covert mechanical signals from the middle ear into electrical signals which can transfer info to the auditory pathway in the brain Also maintains balance by detecting position and motion
Position of the inner ear?
Located within the petrous part of the temporal bone Between middle ear and internal acoustic meatus
What is the bony labyrinth?
Bony cavities within the petrous part of the temporal bone Comprised of -cochlea -vestibule -three semicircular canals
What are each of the structures of the bony labyrinth lined with?
Internally with periosteum
Contain a fluid called perilymph
Describe the membranous labyrinth component of the inner ear
Lies within the bony labyrinth
Consists of the cochlear duct, semicircular ducts, utricle and saccule
Filled with fluid - endolymph
What are two openings of the inner ear into the middle ear?
The oval window between the middle ear and the vestibule (stapes attaches to it)
The round window between the middle ear and the scala tympani
Describe the vestibule of the bony labyrinth
-what it has
-what it communicates with
-what is in it
The central part
Has the oval window
Communicates anteriorly with the cochlear and posteriorly with the semicircular canals
Utricle and saccule of membranous labyrinth are within it
What is within the cochlea of the inner ear?
Cochlear duct of the membranous labyrinth - the auditory part of the inner ear
What does the cochlea twist around?
Branches from which nerve are found at the base of the modiolus?
What extends outwards from the modiolus, holding the cochlear duct in position?
What are the two perilymph fluid-filled chambers above and below the cochlear duct?
Scala vestibuli - supeiorly. Continuous with the vestibule
Scala tympani - Inferior to the duct. Terminates at the round window
How many semicircular canals are there?
What are they called?
Anterior, lateral and posterior
Responsible for balance, along with the utricle and saccule
What is the swelling at one end of each semicircular canal called?
What is the membranous labyrinth?
Where is it?
What surrounds it?
Continuous system of ducts filled with endolymph.
Lies within the bony labyrinth
Surrounded by perilymph
Which structures make up the membranous labyrinth?
Three semicircular ducts
Saccule and utricle
What are the walls of the cochlear duct formed from?
Lateral: Thickened periosteum, known as the spiral ligament
Roof: A membrane which separates the cochlear duct from the scala vestibuli - Reissner's membrane
Floor: Membrane whih separates the cochlear duct from the scala tympani - basilar membrane
What is in the basilar membrane?
The epithelial cells of hearing - the Organ of Corti
What are and where are the saccule and utricle?
Two membranous sacs located in the vestibule
Which ducts do the utricle and saccule receive?
Utricle - semilunar ducts
Saccule - cochlear duct
How is balance detected?
Endolymph within the semicircular ducts changes speed or direction when the head is moved.
Sensory receptors in the ampullae of the canals detect the change, and send signals to the brain.
What drains endolymph?
The endolymphatic duct from the saccule and utricle
What is Meniere's disease?
A disorder of the inner ear, characterised by episodes of vertigo, low pitched tinnitus and hearing loss.
What is thought to cause the symptoms of Meniere's disease?
Excess accumulation of endolymph within the membranous labyrinth, causing progressive distension of the ducts.
Resulting pressure fluctuations damage the thin membranes of the ear that detect balance and sound
Arteries supplying the bony labyrinth?
Anterior tympanic branch from maxillary artery
Petrosal branch from the middle meningeal artery
Stylomastoid branch from the posterior auricular artery
Arterial supply the membranous labyrinth?
Labyrinthine artery, a branch of the inferior cerebellar artery aka basilar artery
Divides into three branches
-cochlear supplying the cochlear duct
-2 vestibular branches supplying the vestibular apparatus
Venous drainage of the inner ear?
Labyrinthine vein, empties into the sigmoid sinus aka inferior petrosal sinus
Inner ear innervation?
Vestibulocochlear nerve (CN VIII)
Branches into the vestibular nerve (balance) and cochlear nerve (hearing)
Through which structure does the vestibulocochlear nerve enter the inner ear?
Internal acoustic meatus
Which other nerve passes through the inner ear but does not innervate anything?
What does the vestibular nerve innervate?
Enlarges to form the vestibular ganglion, then splits into superior and inferior parts
Utricle, saccule and semicircular ducts
What does the cochlear nerve innervate?
Enters at base of modiolus and its branches pass through the lamina to supply the receptors of the Organ of Corti