sound - chemoreception

sound detection: what is sound?

• its changes in air pressure

  • airpressure is determend on how many molecules of air there are in space

• changes in air pressure: frequency; cycles per second (hz: hertz)

• changes in airpressure gives us sound waves

  • these sound waves hit our tympanic membranes in our ears causing it to flex back and forth

Pitch and Intensity

we can have increased and decreased pitch and intensities

• pitch: frequency of pressure changes

• intensity: amplitude of pressure changes

How sound waves travel through our ears

1. Sound waves strike the tympanic membrane and become vibrations

2. the sound wave energy is transfered to the 3 bones of the middle ear which vibrate them

3. the stapes is attached to the membrane of the oval window. vibrations of the oval window create fluid waves within the cochlea

4. the fluid waves push on the flexible membranes of the cochlear duct

5. energy from the waves is transfered across the cochlear duct into the tympanic duct and is disipated back into the middle ear at the round window

6. hair cells with in the cochlear duct create AP’s in the sensory neurons of the cochlear nerve

Sound Waves → Ear Canal → Tympanic Membrane (Eardrum) → Malleus → Incus → Stapes → Oval Window → Cochlea (Fluid Vibrations) → Basilar Membrane → Hair Cells → Electrical Signals to the Brain

Hearing

• hair cells are located on basilar membrane in the cochlea

• tips of hair cells are bent by basilar membrane movement

• bending tips of hair cells causes AP firing

Organ of corti

where the production of hair cells are made (this is within the cochlea)

auditor system: hair cells

• stereocillia: hair cells within the inner ear

  • these cillia move right and left

    • L direction of cilia: upward movement of basilar membrane

    • R direcetion of cilia: upward movement of basilar membrane

• Hair cells modulate release of NT’s: change in AP frequency above spontaneous frequency

• moving these hair cells causes more APs and releases more NTs

  • More NTs = more APs

how do we mamals distingusih different sound frequencies (pitch)?

• human hearing: 20-20000 hz

• we have to look at the basal membrane and the hair cells

  • basilar membrane resonates with frequencies

    • the hair cells on top of the basilar membranes location codes for the frequencies

basilar membrane resonates with frequencies

• High frequency sound waves move membrane closer to stapes; lower frequency sounds closer to distal end.

• THUS: Hair cell location on membrane creates codes for sound pitch.

• different regions of basilar membrane project to different areas of cortex: ionotopic representation

• High frequency sound waves move membrane closer to stapes, lower frequency sounds closer to distal end

sensory coding for pitch discrimination

the map to show where on the cochlear the basal membrane flexes for certian frequencies

auditory pathways to the brain

• information from the ear (the vibration energies - AP) go to the auditory complex via cochlear nerve

• auditory structures are bilateral, messages can cross over between 2 sides

  • info from R/L can be sent to the R and L side of auditory cortex in the brain

human auditory cortex

• this cortex just like the cochlear map in our ears has a map telling it what frequencies are occurring

  • Only sense where you have a neural map

• neurons, responding to particular frequencies, are arranged in a gradient, with cells responding to decreased frequency tones at one end and cells responding to increased frequency tones at the other end of auditory cortex