Flashcards in Lecture 4: The Auditory Pathway (unfinished) Deck (30):
Why is the middle ear a 'high risk space'?
- Connected to nasopharynx - prone to infection
- Connected to mastoid air cells - infection may spread to middle cranial fossa
- Internal jugular vein lies inferior - thrombosis risk
- Internal carotid artery lies anterior - link to pulsatile tinnitus
- Traversed by chorda tympani and facial canal - infection risk
What is the inner ear filled with?
Perilymph - like extracellular fluid i.e. high in Na, low in K
Name the cavities in the petrous part of the temporal bone?
What is the cochlear duct?
Closed tube within the cochlea.
What is the cochlear duct filled with?
Where is the inner ear located?
Within the petrous part of the temporal bone.
What is the function of the external ear?
To transmit sound waves.
What is the function of the middle ear?
To convert sound waves to mechanical energy.
What is the function of the inner ear?
To convert mechanical energy into electrical energy (i.e. action potential).
What two chambers are formed within the cochlea by the cochlear duct.
- Scala vestibuli
- Scala tympani
Where are the scala tympani and scala vestibuli continuous?
How does the cochlea work?
Hydraulic pressure created in the perilymph, by the vibrations of the stapes pass to the apex via the SV. Pass through the helicotrema and descend via the ST to the round window. As the fluid moves around the cochlea it deforms the fluid, endolymph, in the cochlear duct.
What forms the roof and floor of the cochlear duct?
Roof - Vestibular membrane
What is the name of the auditory receptor?
The Spiral organ of Corti
What is contained within the spiral organ of Corti?
What are hair cells embedded in?
How is the spiral organ stimulated?
The spiral organ is stimulated by the deformation of the cochlear duct by the perilymph in the surrounding SV and ST
What are the features of primary auditory fibres?
- Axons of bipolar neuron in
- Forms the cochlear nerve which
becomes part of vestibulocochlear nerve (CNVIII)
Where does the vestibulocochlear nerve (CNVIII) enter the brainstem?
Where do the primary auditory fibres synapse with secondary neurones?
In dorsal and ventral cochlear nuclei
What are the auditory centers in the brainstem?
- Medial geniculate nucleus of thalamus
- Inferior colliculus
- Superior olivary nucleus
- Cochlear nuclei
Which two inputs does the auditory pathway have to compare?
What name is given to the primary auditory cortex?
What are the secondary auditory areas?
Broca's area - anterior (parietal), involved in motor/production of words
Wernicke's - posterior (temporal), sensory/understanding
Which division of the MCA supplies Broca's area?
Which division of the MCA supplies Wernickes's area?
What are the functions of the descending auditory pathways?
- Reflex head and eye movements (CN III(3), IV(4) and VI(6)) ie in reaction to sound.
- To stapedius via CN VII(7) and tensor tympani via CN V3. Prevents damage during loud noise.
What effect does a unilateral lesion have on hearing?
Little. The ability to localise sounds may be impaired.
What is conductive deafness?
Defect of sound transmission up to spiral ganglion