Human audible zone
20-20,000 Hz
Amplitude
Height of sound waves indicate loudness measured in dB. Greater amplitude = greater vibrations = louder sounds.
Frequency
Distance between peaks indicate pitch measured in Hz. Higher frequency = higher pitch.
Purity
Number of layered frequencies dictate timbre. Timbre represents the complexity of a sound.
The 3 sections of the ear
External, middle, and inner
External Ear
Collects and amplifies sound waves, including the pinnae, ear canal and ear drum.
Pinna
Folded cone in various sizes and shapes that collect sound waves
Ear canal
Narrows towards ear drum to amplify the sound waves
Ear drum
Thin membrane that vibrates at the same frequency of the incoming sound waves
Middle Ear
Contains ossicles for amplification, including the stirrup, anvil, and hammer
Hammer
First ossicle to amplify sound onto the anvil; also called malleus
Anvil
Second ossicle to amplify sound onto the stirrup; also called incus
Stirrup
Last ossicle to amplify sound into the oval window; also called stapes
Inner Ear
Sound signals are converted to electrical signals, including the cochlea, oval window, round window, basilar membrane and hair cells.
Basilar Membrane
Runs the length of the cochlea and is displaced by fluid moment. It gets wider towards the apex. Low frequencies vibrate near the apex, whereas high frequencies vibrate near the window openings.
Cochlea
Fluid-filled tube coiled like a snail shell (35mm long), containing the basilar membrane.
Oval window
Connects to cochlea from ossicles and vibrations displace cochlear fluid.
Round Window
Accommodates for the movement of the fluid by bulging in or out. It pushes inward to push the fluid in the cochlea, and will push outward to restore fluid balance.
Hair cells
Auditory receptors that converts the fluid waves into neural impulses. There are inner and outer hair cells. (4:1outer hair cells to inner hair cells ratio) They release a neurotransmitter and synapse with bipolar cells whose axons make up the cochlear nerve
Inner hair cells
- less numerous
- more connections to brain
- sends pitch information
- myelinated
Outer hair cells
- more numerous
- fewer connections to the brain
- amplifies sound
- unmyelinated
Cochlear nucleus
Neurotransmitters from the hair cells triggers EPSPs in the cochlear nerve fibres, which then sends signals to the cochlear nucleus in the hind brain. The cochlear nucleus then processes different aspects of sound in the dorsal and ventral streams
Tonotopic Organization
Auditory system is organized by frequency and the Basilar membrane maps onto the primary auditory cortex.
Apex = low frequency = start of A1.
Base = high frequency = end of A1.
Auditory Localization
Ability to determine where a sound is coming from because our ears are separated; determined by arrival timing and intensity
