How do we hear, taste and smell? Flashcards
What is audition and what is it important for?
Hearing - the sense of detecting sounds
Important for signalling and communication
What is sound?
The movement or vibration of objects - movement alternately squeezes air molecules together and pulls them apart - this pressure wave spreads outward from the source of sound to the listener
What is frequency and pitch?
rate of vibration in cycles per second i.e. Hertz (Hz)
What is amplitude and loudness?
intensity of sound i.e. decibels (dB)
What does your ear have to do to hear sound?
- direct the sound waves into the hearing part of the ear
- Sense the fluctuations in air pressure
- Translate fluctuations into an electrical signal that brain can understand
What is complexity and timbre
Most tones have a mixture of frequencies
Complexity determines timbre (eg. difference between violin and flute)
What does the external ear do?
Captures, focuses and filters sound
What are the 2 parts of the external ear?
Pinnae and ear canal
What is the pinnae?
funnel-like structure that channels sound into the ear
What is the function of the ear canal?
Narrowing amplifies sound waves towards the eardrum (tympanic membrane)
What does the middle ear do?
Concentrates/amplifies sound energies
What are the ossicles?
bones of the middle ear
Malleus (hammer), Incus (anvil) and stapes (stirrup)
What does the inner ear do?
Converts vibrational energy into waves of fluid
Auditory part of the vestibulocochlear nerve
What is the cochlea in the inner ear?
The auditory part of the vestibular nerve
Coiled structure (bony exterior with hollow compartments filled with fluid)
What happens in the cochlea?
Vibrations from ossicles to oval window membrane sends waves through fluid filled cochlea
- Vibration transmitted to organ of corti via basilar membrane (structures in cochlea_
- movement of sensory hair cells transduce sound waves into neural activity which is sent along auditory nerve to brain
What does the tonotopic basilar membrane do?
Vibrates when stapes moves fluids of inner ear.
Different sound wave frequencies cause peak bending of membrane at different points along its path
What is the organ of corti and what does it do?
includes three rows of outer hair cells and one row of inner hair cells. Vibrations caused by sound waves bend the stereocilia on these hair cells via an electromechanical force.
What is the auditory pathway to the brain?
The auditory nerve transmits auditory information up a series of nuclei to the cortex where perception occurs. These nuclei include 1) cochlear nucleus, 2) superior olivary nuclei, 3) lateral lemniscus, 4) inferior colliculus, and 5) medial geniculate nuclei.
Where is the primary auditory cortex?
In temporal lobe within Heschl’s gyrus in the sylvian fissure
Tonotopic
Where is the secondary auditory cortex?
Surrounds primary auditory cortex
Planum temporale - behind Heschl’s gyrus and superior temporal gyrus
How do we hear pitch?
Enabled by tonotopic organisation
Each hair cell responds to a small range of frequencies based on location on basilar membrane.
Bipolar cell axons (form cochlear nerve) connect to only one hair cell each (order of these reproduces tonotopic representation)
- systematic representation maintained all the way to primary auditory cortex
(temporal coding - the rate of sound waves - also helps)
How do we hear loudness?
Larger pressure changes produce more intense basilar vibration –> greater shearing of hair cells –> cochlear bipolar neurons fire more frequently
From this, auditory system determines changes in loudness
How do we detect location?
Difference in timing at each ear and relative loudness are detected by nuclei in the brain stem that receive input from both left and right ventral cochlear nuclei.
Superior olive (medial) neurons respond to differences ARRIVAL TIME between each ear.
Superior olive (lateral) and trapezoid body neurons respond to differences in LOUDNESS
This info is conveyed to inferior colliculus in midbrain where an auditory spatial map aids localization of sound