Lecture 5 - Audition Flashcards
How is sounds generated?
Objects vibrated, which vibrates the surrounding air moleculues - these air molecules condense and rarefy = producing waves. These waves travel away from object and stimulate receptors in our ears
Define physical dimensions of sounds
Amplitude - size from peak to trough - loudness
Frequency - number of waves in a give time - pitch (hz)
Timbre - Complexity of wave
What is in the anatomy of the outer ear?
Pinna -> Ear (auditory canal)
What is in the anatomy of the middle ear?
Tympanic membrane -> mallues (hammer), Incus (anvil) and Stapes (stirrup) - these are the 3 ossicles -> transmit info to oval window of cohclea.
This oval window is caused to vibrate by the movement of the ossicles
What is in the anatomy of the inner ear?
Cochlea (sensory organ filled with fluid) - contains the receptive organ- ORGAN OF CORTI
What is the purpose of the organ of corti?
Changes physical movements from ear drum, ossicles and oval window to electrical signals that transmits to brain. Changes sounds vibration into receptor potential via a bending of hairs
What are the 3 main structures of the organ of corti?
- Hair cells (auditory receptors)
- either outer hair cells, or inner hair cells - Basilar membrane (flexible)
- Tectorial membrane (rigid)
How are hair cells attached to organ of corti/
Hair cells are anchored to flexible basilra membrane, outer hair cells attached to tectorial membrane as well
How do hair cells create signals?
Basilar moves relative to tectorial membrane - causes cilia to bend/ move, this produces receptor potentials, not action potentials
how does sound frequency change basilar membrane?
Different strengths of vibrations cause parts of basilar membrane to bend/ flex back and forth.
Part of basilar membrane in cochlea that bends most depnds on frequency of sound
• high frequency - end nearest oval window
• low frequency - end furthest from oval window
What are the two types of hair cells?
Inner - 1 row, cilia do not attach to tectorial membrane
outer - 3 rows, cilia attach to tectorial, act as a cohclear amplifiier
What are the 2 ways the tecotrial membrane bends hairs?
directly - through conncetion - when basilar moves, hairs attacted to tectorial move
Indirectly - through fluid movement
What do hair cells connect to and send info via?
Connect to bipolar cells, transmit info via cochlear nerve
Define Cilia tip links
Tip links are under a small amount of tension at rest
- highly flexible, fine, elastic filaments
- connect to one cilium (singular) to the next
- its the stretching, bending and flexing of these that cause membrane/ graded potentials
- organised in tallest to shortest
What does relaxing the tip link do
- Stretching tallest to shortest
- causes hyperpolarisation - ion channels open
- decreeases receptor potentials
- Decreases the amount of NT being released onto the bipolar cell
What does stretching the tip link do?
- Stretching shortest to tallerst
- causes depolarisation via ion channels opening
- increases receptor potentials
- increases the amount of NT being released onto cell
Describe the central auditory pathyway
- Organ of corti (auditory nerve)
- Cochlear nucleus (medulla)
- Superior olivary complex (medulla)
- Inferior colliculus (midbrain)
- Medial geniculate nucleus (thalamus)
- Auditory cortex of temporal lobe
What are the 2 streams of the auditory cortex?
Ventrall stream
- what stream - analysis of complex sounds, terminates in parabelt region in anterior temporal lobe (short stream)
Dorsal stream
- Where system - sound localisation, terminates in posterior parietal cortex
Which hemisphere receives info from which ear
Both get info from both ears, but mainly contralateral (side specific)
How is loudness detected?
Signalled by rate of firing - louder sound produce more vibrations so more bending force on hair cell
This leads to more NT release so a higher rate of firing in bipolar cells
What are the two ways that pitch is detected?
- Place coding - for moderate/ high freqs
2. Rate coding - for low freqs
Define place coding for pitch
Codes frequency by different locations on basilar membrane - higher frequences are closer to oval window, lower are towards the apex end
Firing of particular neurons in cochlear nerve tells brain which freqs are presnent
Define rate coding for pitch
Detected by neurousn that fire in synchrony with movement of basilar membrane at apex - Codes frequency by firing rates of neurons in auditory system
How is timbre detected?
Sounds contain many frequencies (overtones) - but we perceive a fundamental frequency
- different portions of basilar membrane respond to each overtone - when put together, they formed a unique anatomically coded pattern of activity in cochlear nerve
- nerve activity is then identified by circuits in auditory association cortex
