Lecture 7 + Assignment 6 Flashcards
Sound waves
Longi vs transverse
Wave of compression (particles close) and rarefaction (particles far)
Longitudinal: Pulse and vibration the same direction
Transverse: Pulse left/right, vibration up/down
Sound wave measurements
Speed = distance/time = wavelength/period
Frequency (Hz or s^-1) = 1/period
Speed = wavelength x frequency
Human voice frequency and wavelength
Men
- 100 Hz
- 3.44 m
Women
- 200 Hz
- 1.72 m
2 things that allow for sound localization
- Interaural intensity difference
- Interaural time difference
Interaural intensity difference
- sounds louder in the ear that it’s near
bc head muffles sound
Interaural time difference
difference in speed of sound entering one ear vs. the other
brain calculates
Ascending auditory pathways
Destination: primary auditory complex in temporal lobe
Nucleus 1: in medulla cochlear nuclei
Nucleus 2: pons nuclei (ITD and IID) sup. olive
axons from the ear to the 8th cranial nerve (auditory nerve)
- spiral ganglion
Cranial nerves
General
Most rostral = 1
Most caudal = 12
don’t enter the spinal cord
enter through fossa holes in the cranium bone surrounding brain stem
Auditory cortex
tonotopic representation based on frequencies
closer to front corresponds with apex of cochlea
closer to back corresponds to base of cochlea (20 000 Hz)
Humans can hear what frequencies
20 Hz - 20 000 Hz
The superior olivary complex
Where is it
contains 2 nuclei for sound localization:
- LSO (lateral superior olive)
- interaural loudness/level difference - MSO (medial superior olive)
- interaural time difference
in mid-pons
Lateral superior olive
interaural intensity difference
for high frequency sounds > 2000 Hz
smaller wavelengths than the diameter of the head (20cm)
LSO sound localization
each cochlear nucleus
excites:
- the ipsilateral LSO (same side)
- the contralateral MNTB
MNTB inhibits the ipsilateral (to itself) LSO
Medial superior olive
monitors interaural time difference for low-frequency sounds
under 2000 Hz
where there is NO head shadow
so do time instead of intensity
MSO sound localization
Jeffress Model
- MSO gets input from both sides
- different axon lengths to same nucleus in MSO
- one will get EPSPs from both sides at the same time
coincidence detection = tells you location from each ear
Parts of the human ear
pinna
concha (shell/bowl)
external auditory meatus
tympanic membrane
Middle ear:
malleus
incus
stapes
Eustachian tube
Inner ear:
oval window (membrane)
vestibule
cochlea
round window
semicircular canals
hair cells
What does the eustachian tube do
- equalizes pressure in the middle and outer ear
- opens into throat
- for tympanic membrane
- allows it to not bulge and burst
- so it can vibrate