sound

what is sound?

air particles vibrate and initiate sound waves that carry vibrations through the air

• is mechanical energy; has to transform energy into receptor

things we should know

1. location of sound

2. frequency

3. amplitude

frequency

tone or pitch (how frequently the tympanic membrane deflects)

• energy is directly proportional to frequency

• # of wavelength compressions / sec (more waves = higher pitch)

amplitude

loudness (how far the tympanic membrane deflects)

• peak to trough (higher peak / trough = louder sound)

structure of the ear

3 divisions…

1. inner ear

2. middle ear

3. outer ear

outer ear

1. pinna

2. external auditory meatus

pinna (ear lobe)

funnel shaped outer ear made of skin and elastic cartilage

function: catches sound waves and passes them along external auditory meatus

external auditory meatus

channel leading sound from the pinna to the tympanic membrane

middle ear

1. tympanic membrane

2. ossicles

3. eustachian tube

air filled space that amplifies force of sound waves so they’re stronger when they enter the inner ear

tympanic membrane (eardrum)

sound collides with membrane and catches frequency & amplitude and passes sound to auditory ossicles

ossicles

1. 3 bones in a small air filled chamber

2. used to focus the pressure of sound waves so that they’re strong enough to move fluid in inner ear (forms a chain that conducts eardrum vibrations and transfer force over to oval window)

bones

1. malleus (hammer)

2. incus (anvil)

3. stapes (stirrup)

bones have pivot points that act as fulcrums

oval window

second membrane that covers a hole in bone of the skull; transfers energy of force to the fluid in cochlea

malleus

one end connects to inner ear drum and moves back and forth when drum vibrates other end connects to incus

incus

connected to malleus + stapes

stapes

connected to incus + oval window

inner ear

functions:

1. converts the physical movement of the oval window into neural signal the brain can identify as sounds

2. help maintain equilibrium

anatomy of inner ear

1. cochlea

2. vestibular apparatus

vestibular apparatus

not involved with auditory system involved in homeostasis and balance

• uses fluid + sound waves

• controlled by movement of head

• has 3 canals; each canal can detect a different type of head rotation

• every canal widens @ its base into sac like structures

functions of middle ear

1. cochlea is filled with fluid

2. requires more force to displace fluid than air

3. bones in middle ear amplify the pressure needed by the cochlea

movement of the bones

1. malleus is displaced in response to tympanic membrane

2. then top of incus is pulled towards outer ear and pushes bottom to inner ear

3. stapes is constantly pushed forward against the oval window

cochlea

transduces the mechanical displacement of the oval window into a neural signal

• the energy imparted on the oval window causes the fluid in sections of cochlea to resinate (vibrate)

anatomy of cochlea

1. chambers of cochlea (3)

2. organ of corti

3. basilar membrane

chambers of cochlea

1. scala vestibuli

2. scala media

3. scala tympani

separated by membranes

scala vestibuli

above vesticular membrane

• oval window is located here

scala tympani

underneath basilar membrane

scala media

within the central region of cochlea

• where corti is located

eustachian tube

tube that allows air to come from respiratory system into middle space

• helps make pressure the same in ear as outside

membranes that separate cochlea chambers

1. vestibular membrane

2. basilar membrane

basilar membrane

helps to encode pitch / frequency

• made of fibers that get longer the farther down they go (base to apex)

• resinates (vibrates and can move)

• when moves membrane causes hair cell to sheer

round window

stops sound wave that is formed by oval window

helicotrema

physical connection between scala vestibuli and scala tympani where fluid is continuous between both layers

base of basilar membrane

short and stiff

• vibrates to high pitch

apex of basilar membrane

long and loose

• vibrates to lower pitch

fibers of basilar membrane

resinate (vibrates) @ different frequencies; different parts of the membrane vibrate depending on the pitch of the sound

transduction of sound (mechanical displacement)

transduction starts when part of the basilar membrane move and the hair cells in organ of corti sheer

organ of corti

• has hair cells (auditory receptor cell)

• corti is located in the scala media

organ of corti structure

1. outer hair cells

2. inner hair cells

3. tectorial membrane

4. reticular membrane

5. basilar membrane

6. stereocilia

7. spiral ganglion

auditory receptors of corti

hair cells

• tip of hair cells are stereocilla

tectorial membrane

can’t move; involved with the bending of the stereocilia and shearing

transduction

1. bending of stereocilia is critical event (starting point)

2. hairs extend above the reticular membrane and come in contact with the tectorial membrane

3. when basilar membrane moves in response to the motion of the stapes; the stereocilia bends and flaps open up and open up pores (shearing)

4. stereocilia cells will either depolarize of hyperpolarize depending on the direction hairs bend

5. when stereocilia sheers = k+ channel opening on stereocilia and hair cell depolarizes

6. result of depolarization = calcium channel is activated + influx of calcium causes release of synaptic vesicles from end of hair

7. neurotransmitters release

reticular membrane

in between basilar membrane and tectorial membrane

shearing

when flaps that covers on the stereocilia open up after the bending of stereocilia and K+ channel opens

transduction: step 1

bending of stereocilia is critical event (starting point)

transduction: step 2

hairs extend above the reticular membrane and come in contact with the tectorial membrane

transduction: step 3

when basilar membrane moves in response to the motion of the stapes; the stereocilia bends and flaps open up and open up pores (shearing)

transduction: step 4

stereocilia cells will either depolarize or hyperpolarize depending on the direction hairs bend

transduction: step 5

when stereocilia shears = k+ channel opening on stereocilia and hair cell depolarizes

transduction: step 6

result of depolarization = calcium channel is activated + influx of calcium causes release of synaptic vesicles from end of hair

transduction: step 7

neurotransmitters release

sac like structures

utricle + saccule; full of hair cells that sense motion of the fluid

how is amplitude encoded

hair cells

1. can increase firing rate (how many times can NT release)

2. more activated hair cells = louder / more amplitude