Auditory Pathway Flashcards
Which skull bone does the ear sit around?
Temporal bone
What 2 parts can the temporal bone be divided into?
- Squamous; lateral, flat portion
- Petrous; rough portion
The ear is divided into 3 portions. What are they?
- External
- Middle
- Inner
The external ear can be divided functionally and structurally into two parts. What are they?
- Auricle (or pinna)
- External acoustic meatus
In the middle of the auricle is a hollow depression. What is it called? What does it continue into the skull as?
Concha - continues into the skull as the external acoustic meatus
Function of the concha/auricle?
funnels sound waves into the ear canal via the external acoustic meatus
Where does the external acoustic meatus end?
Tympanic membrane
Function of the
a) external ear
b) middle ear
c) inner ear?
a) receives sound waves
b) transmits sound waves into mechanical waves
c) transmits sound waves into electrical waves
Describe the composition of the external acoustic meatus
- Lateral 1/3rd of the canal is cartilaginous
- Medial 2/3rds of the canal is bony, made up of temporal bone
In the middle ear, how are sound waves transmitted into mechanical waves?
Vibration of ossicles
What are the ossicles? Names?
3 bones of the middle ear are the auditory ossicles that link the tympanic membrane to the oval window of the internal ear.
- Malleus (most lateral)
- Incus
- Stapes (most medial)
What are the smallest bones in the body?
Ossicles
What is the middle ear? Location?
Air filled space in the petrous part of the temporal bone
What separates the middle from the external ear?
Tympanic membrane
Which ossicle is in contact with the middle ear?
Stapes
Function of the ossicles?
- Vibrate to transmit/amplify sound waves into cochlea ear
- Bones vibrate to amplify sound
Ossicles can can calcify with age, becoming less flexible and less able to vibrate. What can this cause?
This can cause conductive hearing loss. May be progressive or complete.
How is the middle ear in contact with the nasopharynx?
Via the Eustachian (auditory tube)
What is the Eustachian tube? What does it connect?
Tube that connects nasopharynx to the middle ear
3 major functions of the Eustachian tube?
- Drains fluids into nasopharynx
- Ventilates the middle ear
- Equalise pressure between external environment and pressure on the inside
Why are infants more prone to ear infections than adults?
As they have a smaller and more horizontal Eustachian tube –> more direct route for infections to access the tube and therefore the middle ear
As we grow, how does our Eustachian tube change shape?
Becomes more vertical with age
Is the Eustachian tube typically held open or closed?
Open
How is the Eustachian tube affected when there is a big change in atmospheric pressure e.g. airplane, scuba diving?
In certain situations when there is a big change in atmospheric pressure, then the tube is held more tightly closed e.g. airplane, scuba diving (why your ears hurt)
Why does swallowing/opening mouth relieve ear pain in airplane/scuba diving?
Swallowing, opening mouth, or closing nose and expelling air can forcefully open the Eustachian tube
Where does the Eustachian tube drain fluid into?
Nasopharynx
The middle ear is a high risk space for infection. Why is this?
Is connected to nasopharynx via Eustachian tube –> prone to infection
What is infection of the middle ear called?
Otitis media
What 4 major infections can a middle ear infection lead to?
- Connect to mastoid air cells (of mastoid process) –> infection may spread across these structures to middle cranial fossa and potentially brain
- Internal jugular vein lies inferior to middle ear –> infections of middle ear can spread to IJV and damage lining leading to thrombosis risk
- Internal carotid artery lies anterior and inferior –> link to pulsatile tinnitus
- Traversed by chorda tympani and facial canal – infection risk of facial muscles, tongue, stapedius muscle, lesser petrosal nerve and parotid gland
What is pulsatile tinnitus?
Perception of a sound without external sound, sound corresponds to heart rate and can be caused by increased blood flow through arteries in the middle ear.
Infection of which vessel can lead to pulsatile tinnitus?
Internal carotid artery
Where is the inner ear located?
In the petrous part of the temporal bone
The inner ear is composed of 2 special sense organs. What are they? Function of each?
- Vestibular system; balance and equilibrium
- Cochlear system; hearing
Shape of cochlea?
Snail shaped
Frequencies of sound are detected by different areas of cochlea.
a) where are lower frequency sounds detected?
b) where are higher frequency sounds detected?
a) apex of cochlea
b) base of cochlea
What is the range of frequencies that humans can hear?
between 20-20,000 Hx
The inner ear has two main components. What are they?
- Bony (outer) labyrinth
- Membranous (inner) labyrinth
These are fluid filled cavities.
Describe the bony labyrinth. What structure is it composed of? What fluid does it contain?
- 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.
- All these structures are lined internally with periosteum and contain a fluid called perilymph.