IB 202 Hearing and Equilibrium

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IB 202 Hearing and Equilibrium

• Daniel Welsh
• dwelsh_at_life.uiuc.edu
• April 25, 2008

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Reminders from Becky Review Questions will be
posted by next Wednesday, April 30. Review
Session will be on May 5 from 445 to 600 PM  at
Chem Annex 112.  The final is 130-430 on May
7. If your TA is Daniel, then the final is in
196 Lincoln Hall. Otherwise, the final is in
here, 103 Mumford.
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Outline
I. Hearing A. Invertebrates B.
Mammals C. Fish Amphibians II.
Equilibrium A. Invertebrates B.
Mammals C. Fish Amphibians III. SIB
Evaluation/Survey
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Hearing- Invertebrates

• Two main ways to detect sounds
• 1. Hairs on body
• -vibrate in response to sound waves
• -vary in stiffness and length
• 2. Tympanic Membrane
• -thin sheet stretched across an internal air
  space
• -localized on different parts of the body
• -pathway sound waves ? tympanic membrane ?
  connected nerves ? brain

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Hearing- Mammals

• More complex than invertebrates, but still very
  similar
• Divided into three main parts
• outer ear
• middle ear
• inner ear

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Hearing- Mammals (cont)

• Pathway
• Sound waves in air travel through outer ear until
  they reach tympanic membrane
• Sound waves vibrate membrane, which in turn
  vibrates 3 bones of middle ear
• Malleus
• Incus
• Stapes
• (out?in MIS)

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Hearing- Mammals (cont)

• Pathway
• Stapes transmits sound to the oval window
• -membrane on the surface of cochlea
• Vibration on oval window causes vibration of
  perilymph (fluid) in the cochlea

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Hearing- Mammals (cont)

• Pathway
• Cochlea
• -2 canals
• vestibular
• tympanic
• -vibrations pass through vestibular first,
  then through tympanic

(Side view of uncurled Cochlea)
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Hearing- Mammals (cont)
(cross sectional view of Cochlea)

• Pathway
• As waves move through perilymph of vestibular
  canal, they push down on the cochlear duct
• Pushing down on duct pushes down on the Organ of
  Corti
• -pushes down on Tectorial membrane, which
  stimulates hair cells in the basilar membrane

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Hearing- Mammals (cont)

• Pathway
• 8. Stimulation of hair cells causes release of
  more neurotransmitters, stimulating adjacent
  neuron of the auditory nerve
• 9. The information is then carried to the brain

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Hearing- Mammals (cont)

• Two Components of Sound Wave
• There are two main components of the sound wave
  that are detected and used by the auditory
  system
• Volume- Amplitude
  (height of wave)

• Pitch- Frequency
• (no. of waves per unit time)

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Hearing- Mammals (cont)

• 1. Amplitude
• larger amplitude louder sound
• -larger amplitude results in stronger pressure
  on the hair cells, thereby causing more action
  potentials (more neurotransmitters
  released)
• Pitch
• - basilar membrane varies in thickness and
  flexibility
• -base narrow and stiff stimulated by higher
  pitch
• -tip (apex) wider and more flexible
  stimulated by lower pitch

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Presbycusis

• A. Presbycusis
• 1. Age-related hearing loss in humans
• -gradual loss in the ability to hear high
  pitched sounds
• 2. Several possible causes, none of which are
  well understood
• a. Decrease functioning/sensitivity of
  tympanic membrane
• b. Reduced functioning of 1 or more middle ear
  bones
• c. Changes in blood supply to ear (from high
  blood pressure, diabetes, heart disease, and
  others)
• d. Reduced ability of auditory nerves to carry
  information
• http//www.msnbc.msn.com/id/24280571/wid/11915829?
  GT140006

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Hearing- Other Types

• 1. Fish- have inner ear, but no tympanic
  membrane and no opening to outside
• -pathway sound waves ? skull ?inner ear ?
  brain
• -inner ear has small calcium carbonate
  particles called otoliths
• -stimulating otolith stimulates connected hair
  cells
• 2. Amphibians
• -have tympanic membrane on outside surface of
  body
• -pathway sound waves ? tympanic membrane?
  middle ear bone ? inner ear ? brain
• -single middle ear bone

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Equilibrium- Invertebrates

• (Equilibrium balance and body position/orientatio
  n)
• 1. Most invertebrates have sensory organ
• called statocysts
• a. Parts of statocyst
• -layer of ciliated receptor cells
  surrounding an open chamber
• -inside chamber are 1 grains of dense
  material called statoliths

2. Pathway a. Gravity causes statoliths to
settle downward b. Once reach bottom of
chamber, stimulating cilia of receptor cells c.
Stimulated cells release neurotransmitters,
stimulating connecting sensory nerve fibers
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Equilibrium- Mammals

• 1. Organs to detect body position and maintain
  balance located in inner ear
• -two organs
• a. Utricle and Saccule (2 parts of same
  organ)
• -located next to oval window
• -detect which direction is up and detect
  body position and accleration
• b. Semicircular Canals (3 canals in total)
• -next to utricle
• -detect angular movements

Semicircular Canals
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Equilibrium- Mammals

• 2. Pathway
• a. Utricle and saccule contain clusters of hair
  cells embedded in a gel called a cupula
• b. Cupula contains otoliths
• c. Cupula (with otoliths) is heavier than the
  endolymph (fluid) in the utricle and saccule, so
  gravity is pulling the cupula down on to the
  hairs of the hair cells
• -causes constant signals to be sent to brain
  indicating which direction is down

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Equilibrium- Mammals

• 2. Pathway (cont)
• d. Changes in angle of body (i.e. changes in
  position of head) change the force on the hair
  cells
• -causes stimulation of some cells that werent
  stimulated before
• -causes some to increase/decrease their
  signals

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Equilibrium- Mammals
Semicircular Canals

• 3. Semicircular Canals
• a. 3 canals (loops)
• -1 for each plane
• side-to-side
• front and back
• up and down
• b. same mechanism of stimulation as for utricle
  and saccule (cupula with otoliths, hair cells,
  etc.)

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Equilibrium- Aquatic Organisms

• In addition to the typical way to maintain
  equilibrium and orientation, fish and most other
  aquatic organisms have a specialized way called
  the lateral line system

Lateral Line System 1. Fish lateral line on
both sides of body
a. series of mechanoreceptors called neuromasts
on body just under the epidermis
b. Small openings (pores) in epidermis allow for
water to enter into lateral line canals
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Equilibrium- Lateral Line (cont)

• Lateral Line System
• Water stimulates clusters of hair cells in the
  neuromasts by bending the cupula (gelatinous cap
  over the hair cells)
• d. Stimulation causes release of
  neurotransmitters, sending signals through
  sensory nerves to brain

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Equilibrium- Lateral Line (cont)

• Lateral Line System
• Used to detect direction of water flow,
  position of body in water, and vibrations in
  water (from prey and predators)

Fish place lateral line in such as way as to
minimize neuromasts firing from water movement
from fins -- reduces excess background noise.
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SIB Evaluation/Survey

• For Bev Hartley (whoever that is), ONLY provide
  comments if you saw her this year

Have a Nice Weekend!