FE: Lecture 3: Cranial Nerve 8 Flashcards
Where do the vestibular and cochlear nerve originate?
the inner ear
auditory- cochlea
vestibule and semicircular ducts- vestibular
What does the cochlea detect?
sound or vibrations in the ear
20-20,000 Hz- human
What does the canals and semicircular ducts detect?
vibrations of the head, 0-10 Hz
static tilt
dynamic movements like linear and angular acceleration
What are the three main features of the external ear?
Pinna- concentrates sound and direction filter
External auditory meatus
tympanic membrane- first to vibrate (external ear ends here)
What is the name of the air filled chamber in the middle ear?
eustachian tube- fills with fluid when you have a cold due to pressure
What bones and muscles comprise middle ear?
malleus, incus and stapes- bones
muscles- tensor tympani cn 5, stapedius cn 7 these both decrease vibration
damage to either nerve cause hyperacusis
What are the two windows of the inner ear?
oval window- pushes air in (hydraulic like)
round window- allows relief out
they both transmit sound mechanically
What is the bony labyrinth in the inner ear?
spaces in the bone that contain vestibule, semicircular canals and cochlear
filled with perilymph
What is the membranous labyrinth in the inner ear?
sacs inside the spaces- utricle, saccule, semicircular ducts, cochlear ducts
these contain endolymph and contain receptor cells
What is the cochlea?
spiral chamber in the petrous temporal bone
How does sound pressure wave move in cochlea?
sounds enters oval window and down the scala vestibuli
sound exits via round window though scala tympani
What is in the cochlear duct?
endolymph and organ of corti sensory receptor
Describe the organization of the Organ of Corti?
hair cells are in basilar membrane which also contact tectorial membrane which amplifies movement of endolymph
Describe of hair cells are depolarized in organ of corti?
any type of vibration depolarizes these hair cells and action potentials can be created and sent to spiral ganglia via primary afferent fibers
Hair cells or stereocilia are what type of gated channels?
mechanical that make synaptic contact with primary afferent fibers
AP encode amplitude of sound as frequency of firing
What is the pathway of an AP from the stereocilia?
- hair cell receptors to spiral ganglia to cochlear nuclei (dorsal and ventral rostral medulla)
How are low and high frequencies discriminated?
due to tonotopic receptive fields- place theory
based on where it is detected in organ of corti
high freq- base of organ
low- apex of organ
What is the definition of deafness?
loss or reduction of hearing
due to loss of amplitude, can be specific to frequency
high frequency loss is common from rock music (loss of hairs)
What different pathologies can cause deafness?
CVA (labyrinth artery), trauma, infections, toxins (penecillin)
What is conduction deafness?
unable to transmit sound energy due to external ear or middle ear damage therefore no AP is ever created
What is sensorineural deafness?
- damage to cochlea/organ of corti- total, high end or notch hearing loss
- acoustic neuropathy- damage to auditory part of CN 8
What is central deafness?
damage to cochlear nuclei
What is the pathway of auditory info from cochlear nuclei to cerebral cortex?
- cochlear nuclei of medulla to inferior colliculus (some fibers )via lateral lemniscus, others may go to superior olive or nucleus of LL first then IC
- inferior colliculus to medial geniculate nucleus of thalamus
- MGN to primary auditory cortex areas 41/42 in the superior temporal gyrus
Where does info from the left cochlea go?
both sides of cortex
Where are the only two places in the pathway that if damaged will produce ipsilateral deafness?
labyrinth/ cochlear nerve or cochlear nuclei
What type of auditory problems will you have with ipsilateral deafness?
sound localization, problems detecting complex sounds like speech
Where are the auditory cortical areas?
- primary auditory - 41, tone, intensity and localization
- Auditory association cortex- 42, 22, memory of music speech and noise
- speech sensory association cortex- 22, 39, 40 wernike’s area, comprehension of language
What is the one major difference between auditory and vestibular hair cells?
vestibular hair cells have a kinocilia
if flow is toward kinocilia then the cell is depolarized and an AP is created (increased number of AP)
if flow is away then cell is hyperpolarized (decreased number of AP)
