Sound and the Brain

tonotopic map

"frequency map" that lays out which neurons correspond to which frequencies; one end of auditory cortex responds to high frequencies while the other end responds to low frequencies

3 phases of sound waves

1. air waves 2. fluid waves 3. neural impulses

determinants of a vibrating string's frequency

1. material 2. density 3. length

2 basic functions of hearing

1. pitch 2. sound

3 layers of neurons in auditory cortex

1. primary 2. secondary 3. tertiary

the 3 types of sound waves

1. sine waves 2. sawtooth waves 3. compound/complex waves

3 main instrumental sounds

1. vibrating columns of air (woodwinds/wind instruments) 2. vibrating surfaces (percussion instruments) 3. vibrating strings

auditory cortex

A an area in the temporal lobe of the brain that is reponsible for hearing; most highly organized processing unit for sound; interprets/processes basic functions of hearing and contains 3 layers of neurons

ossicles

bones of the middle ear; includes hammer (malleus), anvil (incus), and stapes (stirrup)

sawtooth waves

choppy sound waves with sharp peaks and changes in amplitude below and above the neutral line

compound tones

combination of several types of sound waves; commonly produced in nature

middle ear

contains ossicles (bones of the middle ear) and the pharynx (eustachian tube)

frequency

directly correlated to pitch; number of times a given molecule of air moves back and forth in one second;measured in hertz

pharynx (eustachian tube)

helps to equalize pressure in the middle ear

semicircular canal

liquid filled boney loops that help maintain balance; connected to the cochlea

primary auditory cortex

located in the auditory cortex of the temporal lobe consists of columns of neurons that appear to be tonotopically arranged; each cell in a column is tuned to neural signal from a particular frequency in the auditory input from the cochlea

second and tertiary cortices

located in the auditory cortex of the temporal lobe; identify what a sound is and where it is coming from; do not respond to pitch

oscillograph

machine that measures and graphs pressure variations; variation from the neutral line is measured to show amplitude based on the degree of condensation and rarefaction of sound waves

auditory/cochlear nerve

nerves that send neural impulses from the organ of corti to the auditory cortex of the temporal lobe

first overtone

overtone that is double the frequency of the fundamental tone

second overtone

overtone that is triple the frequency of the fundamental tone

auditory canal

pathway from outer ear towards inner ear; contains ear wax and cilia to protect the ear from foreign objects

outer ear

portion of the ear that contains the auricles and the auditory canal

inner ear

portion of the ear that contains the semicircular canals, the cochlea and the organ of corti; filled with/surrounded by fluid

oscillation

produces pure tones; occurs when a wave moves back and forth in a regular rhythm

sine waves

simplest form of sound waves; hardly ever occurs in nature; consistent "perfect" waves

organ of corti

smallest organ in the body; the organ of hearing; changes liquid waves into neural impulses for the brain to interpret

cochlea

snail shaped, liquid filled part of the inner ear; where air waves are converted into fluid waves; contains the organ of corti

the producers of sound waves/vibrations

the alternation of air between condensation and rarefaction

amplitude

the degree to which the wave varies from the neutral line in either direction; determines the loudness of the sound

condensation

the dense portion of sound waves; occurs on a tuning fork when the prongs move apart and the surrounding air molecules are pushed closer together

displacement/disturbance

the extent to which the sound producer is vibrating; directly proportional to amplitude and volume

rarefaction

the less dense portion of sound waves; occurs on a tuning form when the prongs move together and create a partial vacuum of the surrounding air molecules

volume

the loudness or softness of a sound; directly proportional to the amount of pressure of the air that is displaced by the sound waves

pitch

the result of frequency; directly proportional to frequency or the number of vibrations per second

auricle

the visible part of the ear

tympanic membrane

thin flap that separates the outer ear from the middle ear; vibrates from sound waves and causes movement of ossicles

compound/complex waves

a combination of several types of sound waves; commonly produced in nature

overtones

additional vibrations to the fundamental tone which is usually not as loud or even audible at all but is almost always present; found in halves, thirds, quarters, fifths, etc.