sensing the world: audition Flashcards
functions of hearing
sounds carry important info about others and our surroundings → through hearing we can detect different sound attributes:
- complexity
- intensity
- frequency
what is sound
sounds are produced by vibrating objects; vibrations displace the surrounding medium [liquid,air], creating pressure changes
whta is frequency
- cycles per time unit
- measured in Hertz, 1Hz= 1 cycle per second
percieved as pitch
what is amplitude
- changes in magnitude of sound, same frequency
- measured in decibels [dB]
perceived as loudness
what is complexity
- frequency composition
- varies from a pure tone [single frequency] to a mixture of frequences
perceived as sound quality
what does the outer ear do
captures and
amplifies sound waves.
human sound perception
- the auditory system can detect chnages in air pressure acroos time in a frequency specific manner
- human ears can detect each individual frequency, and its amplititde variation, independnetly
what does the middle ear do
amplifies and
transmit vibrations
what does the inner ear do
translates
vibrations into neural
activity.
outer ear anatomy
- pinnae
- ear canal
- tympanic membrane
middle ear
anatomy + process
- Air filled cavity occupied by ossicles, the three smallest bones in the human body: Malleus, Incus and Stapes.
- Ossicles vibrate in response to tympanic vibration. Amplify and transmit sounds to inner ear (oval window).
what is tonotophy
tones spatial arrangement
pressure transmission 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.
inner and outer hair cells
anantomy
- 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.
Vibration-to-neural-activity translation in inner hair cells
- 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
what are the two types of coding of frequency and amplitude in the cochlea?
- place code
- amplitude code
place code
the two types of coding of frequency and amplitude in the cochlea
Frequency information is coded by the place along the cochlea with the greatest mechanical displacement.
amplitude code
the two types of coding of frequency and amplitude in the cochlea
louder sounds produce larger vibrations of the basilar membrane, making the inner hair cells release more neurotransmitter
auditory pathways
- 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). The tonotopic
representation is preserved up to A1
