Physiology 2.7: Hearing Taste and smell

define sound

• variations of pressure in a medium such as air

  • vibration of an object causes air surrounding it to vibrate

    • eardrum vibrates

      • interpret it as sound

describe sound waves

• consists of alternating zones of…

  • compression

    • molecules are compressed, pressure higher

  • refraction

    • molecules further apart, pressure lower

if there is no elastic medium… there is…

no sound

• ex: outer space

define sound amplitude

• maximum pressure difference between zones of compression and refraction

loudness of sound is directly related to…

amplitude of sound wave

how is sound loudness measured

• reflected by Sound Pressure Level (SPL)

  • decibel units

what is the threshold of sound

0 dB

what sound level causes damage

• greater or equal to 100

what sound level causes pain

• greater or equal to 120

what is frequency and how is it measured

• number of cycles per second

  • measured as cycles per second or Hz

what is the sound frequency range for human ear

• 20 hz to 20,000 hz

what is infrasound

• frequency below human audible range

  • under 20 hz

what is ultrasound

• frequency greater than human audible range

  • greater than 20,000 hz

frequency is also known as…

pitch

describe dolphin hearing

• can hear 75 — 150,000 Hz

  • can hear at much higher frequency

    • 8x higher than human hearing range

describe the external ear

• external auditory canal

  • sound waves enter

• tympanic membrane

  • sound waves causes it to vibrate

• auricle

  • cartilagenous area that guides sound into canal

describe the middle ear

• space between outer ear (tympanic membrane) and inner ear (cochlea)

  • 3 bones

    • malleus

    • incus

    • stapes

  • eustachian tube

what is the function of eustachian tube?

• connects middle ear to upper part of throat and back of nose

  • pressure equalization

  • fluid and mucus drainage

identify this

• eustachian tube

what are the 3 bones (ossicles) of the middle ear

• malleus

• incus

• stapes

how do ossicles transmit sound energy

• stapes hits oval window at entrance to cohlea

  • sound is amplified 15 -20 times

    • because vibration is transmitted through smaller stapes

how much is sound amplified in middle ear

15-20 times

why is amplification of sound necessary in middle ear

• fluid is harder to move than air

describe the parts of the cochlea

• 3 fluid filled chambers parallel to one another

  • scala vestibuli (top)

  • scala media (middle)

    • aka cochlear duct

  • scala tympani (bottom)

• tip is called helicotrema

what is this

tip of cochlea

• helicotrema

describe sound transmission in cochlea

• sound vibration moves fluid through the membrane

  • down scala vestibuli but mostly across cochlear duct

    • basilar membrane also moves travelling down wave according to frequency

describe the organ of corti

• sensory organ with deveral different hair cells

  • cells with stereocilia

where is the organ of corti

• inside the scala media (cochlear duct)

  • rests on top of basilar membrane

what is tectorial membrane

membrane that sits directly above organ of corti

• stereocilia of outer hair cells are directly embedded here

describe tectorial membrane and its role in signal transduction

• movement of basilar movement moves tectorial membrane in windshield wiper fashion

  • outer hair cells are attached to overhanging tectorial membrane

    • cilia bends

      • signal is sent to brain

describe endolymph

• has high K+ and low Na+

describe what happens during mechanical movement of outer hair cells (depolarization)

• stereocilia bundle bends when basilar membrane vibrates due to pressure waves

  • bends in direction of tallest stereocilium

    • K+ enters

      • cell depolarizes

        • opens Ca2+ channels

          • glutamate released

describe what happens during mechanical movement of outer hair cells (repolarization)

• bends in direction away from tallest stereocilium

  • K+ channels close

    • cell hyperpolarizes

      • glutamate stops release

what is this

pinna

what is this

tympanic membrane

what is this

oval window

what is this

• round window

  • pressure relief

    • fluid inside cochlea is relieved here

what is this

scala vestibuli

what is this

• scala tympani

what is this

scala media

• aka cochlear duct

what is the end of the cochlea called

helicotrema

what is this

basilar membran

describe this

• organ of corti

  • has mechanically response cell

Describe the effect of a sound wave on the tympanic membrane

• vibrates in sync with incoming air pressure changes

Describe the function of the ossicles. 

• amplify sound from first ear to third ear

• 
  

describe the vestibular apparatus

• endolymph filled chamber in temporal bone

  • connected to cochlea by cochlear duct

descrube the function of the vestibular apparatus

• sense organs

  • balance, motion, and spatial orientation

describe conductive hearing loss

• hearing loss caused by problem with transmission of sound information across the middle ear to the cochlea

describe senorineural hearing loss

• hearing loss because of damage to cranial nerve

  • deafness

describe presbycusis

• age related hearing loss

  • especially at higher frequencies

describe tinnitus

• ringing in ears accompanied by hearing loss

Which regions of the membrane are most sensitive to higher frequencies? To lower frequencies?

• Higher frequencies

  • Most sensitive at the base of the cochlea (near the oval and round windows). This region is narrow and stiff.

• Lower frequencies

  • Most sensitive at the apex (the top or far end) of the cochlea. This region is wider and floppier/more flexible.

what are chemoreceptors

• receptors sensitive to specific chemicals

  • some respond to internal environment

    • O2 and H+ ion concentration in blood

  • some respond when they come in contact with external environment

    • taste and smell

what are the four basic sensations

• sweet

• sour

• salty

• bitter

which structures contain taste buds

• upper esophagus

• palate

• lingual papillae on tongue

how many taste buds do humans have

• about 10,000

describe chemoreceptors for taste

• taste receptors reacts chemical to substance in mouth

  • located on taste buds in oral cavity

    • mostly on tongue

why are the senses of taste considered a chemical sense

• stimuli for taste are chemical substances dissolved in water or other fluids

what are olfactory receptors

• receptors stimulated by volatile chemical suspended in air

  • located in upper portions of nasal passages

describe how receptor cells are structured

• cellular seal

  • cells joined together by tight junctions, prevent saliva and chemicals from leaking down into deeper layers

• apical membranes

  • membranes are ciliates that extend into a small opening (taste pore)

    • saliva makes direct contact with receptors

• basal membrane

  • the basal ends of taste receptor cells

    • makes contact with primary afferents

      • chemical signal is sent outside the bottom of nerves and carries information directly to brain

describe the taste receptor cycle

• turned over and replaced over every 10 days

  • reduced sense of taste in older adults due to lower rate of turnover of taste receptor cells

What are the taste papillae and where are they found? 

• projections of epithelial layer of tongue that hold taste buds

  • located on tongue

what chemicals in salvia carries the chemicals we taste

tastants

the apical membranes on taste buds are…

• ciliated

  • face outwards toward the surface of the tongue

    • extends into the taste pore to touch the saliva

what is anosmia

• complete loss of ability to smell

what is hyposmia

• diminished ability to smell

  • less severe than anosmia

how many odor differences can humans tell

• 10,000

where are olfactory receptors located

• olfactory mucosa

  • very top of the nasal cavity

describe the turnover rate of olfactory receptor cells

turn over every 2 months

describe specialized primary afferents of olfactory receptors

• custom-built nerve cells designed to detect chemical smells

  • have cilia on dendrites to reach into mucosa

    • float in nasal cavity

      • packed with olfactory receptors

the axons of primary afferents form what

• olfactory nerve

the olfactory nerve goes where?

• travels directly into olfactory bulb in brain

  • instantly perceive and identify smell

how does detection of odorants work

• smell molecules must dissolve in wet mucus layer inside nose

  • carrier proteins (odorant-binding proteins OBPs) help them reach and trigger smell receptors

describe olfactory discrimination

• each olfactory receptor carries only one specific type of odorant receptor protein on its surface

  • over 1000 types of olfactory receptors

• a single odor molecule can activate more than 1 receptor

  • brain recognizes odorant from the unique combination of the different receptor cells activated at once

how many types of olfactory receptor cells are there?

• over 1,000

  • each receptor only carries one type

how many odorants can humans distinguish

10,000 odorants

describe the combinatorial code

• individual odorants activate unique overlapping combinaitons of receptors

  • not just 1-to-1 matches

odors are detected and discriminated when..

several transduction pathways activated from different receptors

what are some causes of olfactory diseases

• sinus/respiratory infections

• deviated septum

• aging

• smoking

• head injury