NEUR531 - Auditory & Vestibular Processing Flashcards
Describe the structure of the auditory system
Describe how the attenuation reflex protects the ear
Describe how the structural properties of the basilar membrane allow discrimation of frequencies
Give a DETAILED ACCOUNT of the process by which pressure waves lead to transduction of hair cell receptor potentials
Describe how outer hair cells function as a cochlear amplifier
Explain how neurons within the auditory pathway encode for sound intensity and frequency
Describe the mechansims by which the auditory system localises sound
Explain the function and mechanism of the vestibulo-ocular reflex
What is sound?
Audible variations in air pressure
What is the sound cycle?
Distance between successive compressed patches of air
What is sound frequency?
Number of cycles per second expresed in hertz (hz)
What frequency is high pitch?
High frequency
Draw out the auditory system
What are the components of the middle ear?
- Tympanic membrane
- Malleus
- Incus
- Stapes
- Eustachian tube (pressure equalization)
What is the middle ear associated with?
Amplification of sound
Attenuation reflexes
What are the components of the inner ear?
Learn the basilar membrane physiology
Understand that the apex is wide and floppy associated with softer sounds 500Hz
Wha is the organ of corti associated with?
What is the basilar membrane assocated with?
What does the bending of stereocilia do?
- Hair cell receptor potentials
- Very sensitive
How is transduction by the hair cells work?
-
What is the function of the cholear amplifier?
Sound transduction
What are the proteins that change length of outer hair cells?
Motor proteins
What are the proteins that are required for outer hair cell MOVEMENT?
Prestins
DRAW OUT THE AUDITORY PATHWAY STEP BY STEP
MGN: Medial geniculate nucleus (thalamus)
Auditory cortex: temporal lobe
Encoding information about stimulus intensity is based on what 2 neuronal factors?
- – Firing rates of neurons
Number of active neurons
Loudness perceived is correlated with… ?
number of active neurons.
Membrane potential of activated hair
cells more depolarised or hyperpolarised
Encodes for sound intensity
Low frequency sounds - Apex
High frequency sounds - move basilar membrane ‘stiff’ areas at base
Are high frequencies phase locked?
No - they are not fixed
Sound from left side, activity in left cochlear nucleus sent to what nucleus?
superior olive
Vertical plane
Do unilateral lesions in the auditory cortex have a significant influence on hearing?
No
Learn the vestibular system
What do the otolith organs do?
- Detect head angle changes
- Macular hair cells respond to tilt
Relies on crystals moving
What is macular orientation associated with
Vertical & horizontal movement
What lymph fluid is associated with the semicircular canal?
- Endolymph fluid
Central vestibular pathways
Draw these out
What is the function of the vestibulo-ocular reflex (VOR)?
Fixating on a point during head movement
What mechanisms does the vestibulo-ocular reflex (VOR) use?
Semi circular canals
KNOW THE 7 STEPS - DRAW THEM OUT
Step by step auditory pathway mechanisms
- Pinna (outer ear) accoustics travel through external acoustic miatus
- acoustic sound waves vibrate the tempanic membrane causing it to compress and decompress
- Tempanic membrane vibrations cause ossicles to vibrate against oval window for cochlear transduction
- Oval window vibrations move basilar membrane within the organ of corti
(if vibrations are excessive, will move out via the round window to avoid damage)
- Basilar membrane vibrations cause hair cells to move, causig stereocillia to bend and send transductions along the tectoral membrane causing depolarization against afferent nerve endings and releasing glutamate
- Glutamatergic afferent excitation APs travel to the spiral ganglion and stimulate cochlear branch of CNVIII (vestibulocochlear nerve)
- CNVIII travels to the pons-medullary junction to stimulate ventral and dorsal cochlear nuclei
8.DORSAL and VENTRAL NUCLEI travel contraleterally to the nucleus of lateral leminiscus AND superior olivary nucleus
9.
What are 2 dorsal cochlear nuclei cells in pons-medullary junction?
Stellate cells
Principal cells
Where do fibers from the basilar membrane travel to (point 1)
Spiral ganglia
Where does the spiral ganglia stimulate?
cochlear branch of CNVIII (vestibulocochlear nerve)
Where does vestibulocochlear nerve (CNVIII) travel to?
ventral and dorsal cochlear nuclei (at pons-medullary junction)
Where do the DORSAL and VENTRAL NUCLEI travel contraleterally to ?
nucleus of lateral leminiscus
superior olivary nucleus
What are the names of the stria traveling from the cochlear nuclei ?
Dorsal
Intermediate
Ventral
Acoustic stria
Where does the nucleus of lateral leminiscus travel to and via what stria?
- Travels via lateral leminiscus to INFERIOR COLLICULUS
What tract is associated with the auditory reflexes?
tectospinal tract (movement of body/head towards sounds)
Where does the inferior colliculus travel to within the thalamus?
MEDIAL GENICULATE NUCLEUS
Where does the medial geniculate nucleus (MGN) travel to for auditory transduction?
The primary auditory cortex (within the superior temporal gyrus)
What does Wernicke’s area associate with?
Speech comprehension
What does the brocas area do?
Speech production
Where does the superior temporal gyrus send signals to?
Wernicke’s and broca’s area
What fasciculus connects the Wernicke’s and Broca’s area?
Arcuate fasciculus
Step by step process for auditory pathway
- Sound waves enter the ear canal and cause the temporal membrane to vibrate.
- Vibrations from the temporal membrane are transmitted to the three small bones in the middle ear: the malleus, incus, and stapes (ossicles)
- The stapes bone transmits the vibrations to the oval window, a membrane-covered opening in the cochlea.
- The movement of the oval window creates fluid waves in the cochlea.
- The fluid waves cause the basilar membrane within the cochlea to move.
- Hair cells in the Organ of Corti, located on the basilar membrane, detect the movement of the fluid waves.
- The stereocilia on the hair cells bend in response to the fluid movement.
- Bending of the stereocilia opens ion channels in the hair cells, allowing ions to enter.
- The influx of ions generates electrical signals in the hair cells.
- The electrical signals are transmitted to the auditory nerve fibers connected to the hair cells.
- The auditory nerve carries the electrical signals from the hair cells to the brainstem.
- Within the brainstem, the auditory signals are relayed to the cochlear nucleus and then to the superior olivary complex.
- From the superior olivary complex, the signals are further transmitted to the inferior colliculus and then to the medial geniculate nucleus of the thalamus.
- Finally, the auditory information reaches the auditory cortex in the temporal lobe of the brain, where it is processed and interpreted as sound perception.
