1.51 The Ear Flashcards
What are the functions of the pinna?
Funnels sound in the ear canal
Externalisation of sound
Localisation of sound in the vertical plane - above and below head
What is the function of the auditory meatus (ear canal)?
Walls secrete waxy cerumen - self cleaning
Captures dust and foreign antibodies
Some amplifying effects
What is the air pressure in the middle ear?
The same as the external air pressure because of the auditory tube
Whats is the function of the middle ear?
To overcome the air - fluid mismatch
This is possible because the tympanic membrane is greater than the foot of the stapes so the pressure at the stapes is much higher
Why is a middle ear needed?
without a middle ear there would poor transfer of sound from air to fluid
What is the malleus and what is it attached to?
The malleus is the first ear ossicle, and it is attached to the tympanic membrane and also to the incus
What are the muscles of the middle ear and what is their function?
Tensor tympani and stapedius - they control stiffness of the ossicular chain.
What are the innervations for tensor ty,pain and stapedius?
Tensor tympani - V3
Stapedius - VII
What are the other two middle ear ossicles?
Incus - middle
stapes - oval shaped window that connects to the inner ear
What is the middle ear reflex?
Contraction of the stapedius muscle
e.g rock concert
The middle ear reflex protects from against loud sounds, not if they are too fast for the reflex to activate - gun shot
What is Rinne’s test?
negative result is when the patient hear the bone conduction longer or louder than the air conduction - hearing loss
Where do the two middle ear muscles attach?
Tensor tympani - malleus
Stapedius - stapes
What is located in the petrous part of the temporal bone?
Inner Ear
What is the petrous part of the temporal bone referred to as?
The osseous labyrinth - filled with perilymph
What is the name of the membronous sack in the osseous labyrinth?
Membronous labyrinth - filled with endolymph
Through which structures does the middle ear communicate with the inner ear?
Oval window - stapes
Round window - filled with membrane
What happens when the stapes pushes the oval window?
The fluid in the inner ear is compressed, this can displace the membrane in the round window - acts as a pressure release
What are the two components of the inner ear?
The cochlea - hearing
The vestibular apparatus - balance
What are the three parts of the cochlea?
Scala vestibuli, scala tympani and scala media (duct)
What are the scala vestibule and tympani filled with?
perilymph (Na+)
How are the scala vestibule and tympani separated to the scala media?
Two membranes
Vestibular and basal membrane
What is the scala media filled with?
Endolymph (K+)
What happens to the cochlea when sound hits the inner ear?
Stapes hits oval window - displaces perilymph
Transferred to the the scala tympani and vestibuli
Fluid displaces basilar membrane
Stereo cilia are deflected because of their resistance against the tectorial membrane
This result in ionic conductance
Stimulates bipolar neurons - to CNS
Where are the cell bodies of the bipolar neurones found?
Central portion of spiral duct - spiral ganglia
