Auditory Flashcards
How does the cortex organize information?
It counts action potentials
If something doesn’t make it to the cortex…
You don’t perceive it.
Receptors for hearing and balance.
Hair cells
How do we measure sound?
Intensity= dB Frequency= Hz
What is in the front of the inner ear? What is in the back?
Auditory is in the front. Vestibular is in the back
What innervates the tympanic membrane and the ear pinna?
V, VII, IX, and X
The stapes sits where?
On the OVAL WINDOW
2 main muscles of inner ear and their functions.
TENSOR TYMPANI- adjusts the pressure of the sound and attenuates the level by pulling malleus a little bit away. (Innervated by CN V)
STAPEDIUS MUSCLE- has a quick reflex to pull stapes from oval window when there is an unexpected loud sound. (Innervated by CN VII)
The 2 labyrinths of the inner ear
Bony
Membranous
What is inside of membranous labyrinth?
High K+ fluid called endolymph
What is inside the bony labyrinth?
Perilymph, which is continuous with the fluid surrounding the vestibular system.
Best way to stimulate fluid movement
Ossicular conduction
What innervates the labyrinths?
Vestibulocochlear nerve fibers (which divide into vestibule and cochlear nerves)
What and where is the “hearing structure”?
The cochlea. It is housed in the modiolus.
What does the cochlea consist of?
(1) Scala vestibui (oval window)
(2) Helicotrema (apex)
(3) Scala tympani (round window)
What are the important structures associated with the cochlear duct?
- It lies between the SCALA VESTIBULI and the SCALA TYMPANI.
- It is separated from them by the Reisner’s membrane above and the Basilar membrane below.
Function of basilar membrane
VERY IMPORTANT
We use this because it would be too limiting to use action potentials to directly code for frequency.
Sounds vibrate based on location on basil membrane (high freq is closer to round window, low freq is closer to oval)
Where nerves sit on basil membrane CODES FOR THEIR FREQ.
What determines the loudness of a sound?
The amount of Action Potentials
Organ of Corti
ORGAN OF CORTI: Sits on Basilar membrane. Is where transduction of pressure waves takes place in the hair cells.
Outer vs Inner row of hair cells
OUTER:
- 3 rows
- In V-shaped pattern (increased surface area)
- Displacement sensitive (cells can change their own sensitivity/length based on amount of movement) ONLY ONES THAT CAN CHANGE OWN SENSITIVITY
- Allows for fine-tuning of auditory signals
INNER:
- velocity sensitive
- 99% of hearing comes from this row (this is why outer row functions to adjust freq.)
- not modifiable by CNS
The first action potential for the sound occurs…
In the bipolar cells, NOT the hair cells
Linkage between hair cells
They are attached via TIP LINKS. Kinocilium are the longest cilium. They are attached to sterocilia. Hair cells are depolarized when the sterocilia bend towards the kinocilium causing the K+ to rush in.
What will cause total deafness in an ear? How does this change once you get past cochlear nuclei?
Any injury to the cochlear nuclei or CN VIII will cause ipsilateral (half of hearing, i.e. one ear) deafness.
Past the nuclei there is shared information and hearing is essentially bilateral so you will still have some hearing.
Tonotopic map tells us…
Which frequency of sounds go to which parts of the cortex (Heschel’s gyrus)
Main 4 nuclei in path of sound to Heschl’s gyrus
(1) Cochlear nuclei
(2) Inferior colliculus
(3) Medial geniculate
(4) Cortex
Location of cochlear vs vestibular nuclei in respect to inferior cerebellar peduncle
Cochlear are LATERAL, whereas vestibular are MEDIAL
Phase locking
Done by hair cells/ bipolar cells. Allows for temporal resolution. Creates a burst of AP’s at the initiation of a new sound. Cells also hyperpolarize when a sound suddenly ends.
Localization of sound
Interpreted by the CNS through 2 methods:
(1) INTERAURAL DIFFERENCE- time between when a sound hits the ear. Whichever ear it hits first while give the direction. (We turn our heads if it’s midline).
(2) PITCH/INTENSITY: When sounds move towards us intensity/pitch increases. They do the opposite when things move away.
The main areas/fibers affiliated with language
WERNICKE’S AREA: For comprehension of auditory signals (understanding language)
BROCA’S AREA: Motor and speech
ARCUATE FASCICULUS: Connects Wernicke’s and Broca’s
Affect of lesion in Wernicke’s Area
They can talk a lot but it doesn’t make sense. There may be real words but they are nonsensical together.
Affect of Lesion in Broca’s area
You can comprehend things but you can’t speak well. You must force each syllable out.
