C: Ear Flashcards
List the structures through which soundwaves pass before reaching the auditory receptors?
1) External auditory canal
2) Tympanic membrane
3) Maleus
4) Incus
5) Stapes
6) Vestibule
7) Cochlea
8) Organ of conti
What is the function of the tympanic membrane?
Convert soundwaves into mechanical vibrations
What are the ossicles?
Small bones found in the ear
What is the function of the ossicles?
Amplify mechanical vibrations
What is the oval window?
Membrane covered window leading from middle ear to inner ear
What is the function of the oval window?
Point of attachment for base of stapes, ends the chain of bones which transfer the vibrations initiated by tympanic membrane to cochlea of inner ear
What is the function of the round window?
Pressure valve which moves out when the oval window moves in
enables improved fluid flow:
allows fluid flow that transfers vibrations to hairs of cochlea
What are the primary and secondary functions of the auditory/Eustachian tube?
Primary - maintain middle ear at atmospheric pressure (equalisation of pressure)
Secondary - drain any accumulated secretions, infections or debris from middle ear space
What is the external auditory canal lined by?
Skin which produces ear wax
What is ear wax made up of? 7
1) Keratinocytes
2) Anti-microbial peptides
3) Alcohols
4) Squalene
5) Cholesterol
6) Triglycerides
7) Lysozyme
How does ear wax travel along the ear canal?
Moved outwards by motions from chewing and other jaw movements
As the skin of the canal grows from inside out - migrating skin cells
What lies at the end of the external auditory canal?
Tympanic membrane
From what is the name chorda tympani (branch of facial nerve) derived?
From its route in the middle ear - it is located behind the tympanic membrane
What is the function of the chorda tympani? 2
1) Taste anterior 2/3 of tongue
2) PS to submandibular and sublingual salivary glands
What forms the lateral wall of the air filled chamber known as the middle ear?
The tympanic membrane
What are the main contents of the middle ear?
The ossicles - maleus, incus and stapes
What epithelium is the middle ear lined by, what are the possible clinical consequences of this?
Lined by respiratory epithelium
Liable to infection in URT disease, it is connected anteroinferiorly to the nasopharynx
Via what is the middle ear connected to the nasopharynx?
The eustachian tube
What is the mastoid antrum?
Collection of mastoid air cells, mucous membrane is continuous with that of the middle ear
Through what opening is the middle ear connected posteriorly to the mastoid air cells?
Aditus to mastoid antrum
Why are meningitis, brain abscess and sigmoid sinus thrombosis potential complications of middle ear infection?
Mucous membrane lining the mastoid air cells is continuous with the mucous membrane lining the middle ear.
Infections can easily spread into mastoid area:
osteomyelitis spreading into the middle cranial fossa.
Brain abscesses, meningitis and inflammatory cell presence can also lead to venous thrombosis
Why is facial nerve damage a potential complication of middle ear infection?
Facial canal transverses the middle ear - if the walls of this become eroded by infection - risk of damage to the nerve
Tensor tympani muscle is located partly in middle ear, what is the nerve supply and function?
Nerve - branch from mandibular nerve (V3)
Pulls the handles of malleus medially
Tensing of the tympanic membrane reduces the force of vibrations in response to loud noises
Stapedius muscle is located partly in the middle ear, what is the nerve supply and function?
Nerve to stapedius muscle (CN7)
prevents excessive movement/ oscillation of stapes bone, controlling the amplitude of sound waves
The inner ear/bony labyrinth is a cavity lying within which bone?
The petrous temporal bone
What fluid fills the inner ear cavity?
Perilymph
What is the membranous labyrinth?
Epithelial sac lying within the inner ear
What fluid fills the membranous labyrinth?
Endolymph
What are the 3 kinds of sensory receptors within the walls of the membranous labyrinth?
1) Maculae - vestibular receptors
2) Christae ampullaris - vestibular receptors
3) Spiral organ (organ of conti) - auditory receptors
In which region of the membranous labyrinth are the maculae located?
Saccule and utricle
The maculae are concerned with what type of sensory information?
Providing sensory info about the static position of the head in space - aiding the maintenance of balance
In which regions of the membranous labyrinth are the christae ampullaris located?
The ampulla of the 3 semi circular ducts which lie within the semicircular canals of the bony cavity of the petrous temoral bone
The christae ampullaris are concerned with what type of sensory information?
Sensory info about changes in the direction and rate of movement of the head
Give 3 structural similarities between the maculae and the christae ampullaris?
1) Have hair cells of the same morphological type (type 1 and 2)
2) Hair cells of both have numerous stereocilia and a single kinocilium
3) The stereocilia and kinocilia are embedded in a ridge of gelatinous glycoprotein in both
In which nerve do the axons of first order sensory neurons associated with these receptors travel to the brainstem?
Vestibular part of CN8 - vestibulocochlear nerve
Injury to the peripheral vestibular system can lead to which 2 conditions?
1) Nystagmus
2) Vertigo
What is meant by nystagmus?
Rapid involuntary movements of the eyes
What is meant by vertigo?
Sensation of motion in which the individuals surroundings appear to spin
What is the cochlear duct?
The part of the membranous labyrinth lying within the snail shaped bony cochlea.
It is filled with endolymph.
The cochlear duct starts at the saccule and ends blindly at the apex of the cochlea.
What is the organ of conti?
Specialised region in the wall of the cochlea duct
The bony cochlea and its enclosed cochlear duct spiral how many times around the central axis of bone?
2.5
What does the central axis of bone contain?
The spiral ganglion - made up of cell bodies of first order auditory neurons
Fluid movement within the middle ear causes which part of the organ of conti to vibrate?
Basilar membrane
What 3 compartments can the cochlear duct be split into, which 2 membranes separate them?
- scala vestibuli
- scala media
- scala tympani
Scala vestibuli seperated from the scala media (containing the organ of conti) by the vestibular membrane
Scala media seperated from scala tympani by the basilar membrane
How does vibration of the basilar membrane differ with differing frequency?
Each point on the basilar membrane (from the base of the membranous cochlear to the apex) vibrates maximally in response to sound of a particular frequency
How does vibration of the basilar membrane lead to action potentials?
1) Basilar membrane vibration causes the hairs (stereocilia) to be deformed against the overlying, gelatinous tectorial membrane.
2) This deformity causes depolarisation/hyperpolarisation of the sensory hair cells and generates action potentials in the sensory nerve fibres synapsing at the base of the cells
Which region of the basilar membrane vibrates maximally in response to sounds of high frequency?
Basilar membrane towards base of cochlear
Which region of basilar membrane vibrates maximally in response to sounds of low frequency?
Basilar membrane further along spiral towards apex
Where are the cell bodies of sensory fibres which contact the hear cells?
Spiral ganglion
Which cranial nerve do the first order sensory fibres join?
Auditory part (cochlear part) of CN8 - vestibulocochlear nerve
What is meant by conduction deafness?
Problem conducting sound waves anywhere along the route through the ear, tympanic membrane or ossicles
What is meant by sensorineural deafness?
Type of hearing loss in which the root cause lies in the inner ear, vestibulocochlear nerve or central auditory processing centres of the brain
