Lecture 10: Sensing the World II - Audition Flashcards
Why do we hear
Sounds carry information about
others and our surroundings
What different sound attributes can we detect
- Complexity
-Intensity - Frequency
What is sound
Sounds are produced by vibrating objects: vibrations displace the surrounding medium (liquid, air), creating pressure changes
What are the psychophysical properties of sound
1)Frequency: cycles per minute, measured in Hertz, 1Hz=1 cycle per second, perceived as pitch: low frequency and high frequency.
2) Amplitude: changes in magnitude of sound, same frequency, measured in decibels (dB), perceived as loudness: high amplitude (looks like high frequency waves) and low amplitude.
3) Complexity: frequency composition, varies from a pure tone (single frequency) to a mixture of frequencies, perceived as sound quality: simple and complex.
Check notion for the waves correction.
Can animals hear different sounds
different animals are sensitive to or can detect sounds within different frequency ranges.
e.g. elephants/moles - lower frequencies
dolphins/bats - higher frequencies
humans - between 20-20k
Do we hear all sounds the same way/with the same weight
Amplitude: different every-day sounds have different intensities.
e.g. leaves rustling/library - quiet
jackhammer/jet takeoff - loud
What sort of sounds are most common
Complex sounds are the most common. Pure tones (single frequency) are rare in nature. A combination of pure tones (single frequency, different amplitudes) make up each complex sound.
Can human detect sound properties independently or all together?
Human ears can detect each
individual frequency, and its amplitude variation, independently.
What can the auditory system detect about the air?
The auditory system can detect
changes in air pressure across
time in a frequency specific
manner.
Describe structure and function of human ear
1) Outer ear captures and amplifies sound waves.
- Pinnae
- Ear canal
- Tympanic membrane
2) Middle ear amplifies and transmit vibrations:
- Air filled cavity occupied by ossicles, the three smallest bones in the
human body: Malleus, Incus and Stapes.
- Tympanic membrane
-Ossicles vibrate in response to tympanic vibration. Amplify and transmit sounds to inner ear (oval window).
3) Inner ear translates vibrations into neural activity:
- cochlea/organ of corti: analyses sound information
-helicotrema
- auditory and vestibular nerves
- vestibular organs: position of head
- oval window and round window
Structure of extended cochlea/organ of corti
When extended flat, we can see the basilar membrane, scala tympani and scala vestibuli, apex and helicotrema.
At base = region tuned to high frequencies.
Mid basilar membrane = mid frequencies.
End/apex= region tuned for low frequencies.
How does the apex compare to the base in the organ of corti
The apex is 5 times wider and 100 times more flexible than the base
Define the role of tonotopy in the basilar membrane of the organ of corti
Tones spatial arrangement
How is pressure transmitted along the canals
- Vibrations of the stapes push and pull the flexible oval window in and
out of the vestibular canal at the base of the cochlea. - Pressure waves deflect the basilar membrane in a frequency specific manner.
- All pressure ends up moving the round window and dissipates.
Give the structures of the cross section of the cochlea: three canals
check notion for structure with annotations
- Tectorial membrane
- Vestibular canal
- Reissner’s membrane
- Middle canal
- Inner hair cells: underneath tectorial membrane.
- Spiral ganglion
- Tympanic canal
- Outer hair cells
- Basilar membrane
Describe the tectorial membrane
- Attached on one end, projects into the middle canal.
- Floats above inner hair cells and touching outer hair cells.
Vibrations of the basilar and tectorial membrane, makes stereocilia bend.
The directions of the hair cells change depending on the movement of the membrane. There is fluid underneath these hairs.
Define and describe how the hair like structures work in a molecular level
Stereocilia: Hair-like extensions on the tips of hair cells. Molecular filaments (tip link) connect the tip of each cilia to neighbouring potassium
channels.
* In resting state (no sound, middle panel)
there is a basal K+ influx and neurotransmitter
release.
* Basilar membrane vibration (right panel)
induce bending of stereocilia which increase
K+ influx, increasing neurotransmitter release
at the cell base. Depolarisation happens, membrane potential increses and makes the inside more postive and calcium comes in the cell through voltage gated calcium channel.
This causes the release of neurotransmitters onto the next receptor cell (perilymph)
How are frequency and amplitude coded
Place code: Frequency information is coded by the place along the cochlea with the greatest mechanical displacement.
Amplitude code: louder sounds produce larger vibrations of the basilar membrane, making the inner hair cells release more neurotransmitter.
What’s the relationship between bipolar cells firing rate and the sound pressure level (dB)
Positive relationship - as the volume increases, the more firing takes place.
What is the auditory pathway
- Hair cell neurotransmitter release
activates bipolar cells that form the
auditory nerve (cranial nerve VIII). - The auditory nerve enters the medulla,
making synapsis in a tonotopic manner
(the frequency spatial representation
of the basilar membrane is
maintained). - A series of ascending projection along
the midbrain ends up in the primary
auditory cortex (A1) through the medial geniculate nucleus. The tonotopic
representation is preserved up to A1.
