Title: IB 202 Hearing and Equilibrium
1IB 202 Hearing and Equilibrium
- Daniel Welsh
- dwelsh_at_life.uiuc.edu
- April 25, 2008
2Reminders from Becky Review Questions will be
posted by next Wednesday, April 30. Review
Session will be on May 5 from 445 to 600 PMÂ Â 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.
3Outline
I. Hearing A. Invertebrates B.
Mammals C. Fish Amphibians II.
Equilibrium A. Invertebrates B.
Mammals C. Fish Amphibians III. SIB
Evaluation/Survey
4Hearing- 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
5Hearing- Mammals
- More complex than invertebrates, but still very
similar - Divided into three main parts
- outer ear
- middle ear
- inner ear
6Hearing- 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)
7Hearing- 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
8Hearing- Mammals (cont)
- Pathway
- Cochlea
- -2 canals
- vestibular
- tympanic
-
- -vibrations pass through vestibular first,
then through tympanic
(Side view of uncurled Cochlea)
9Hearing- 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
10Hearing- 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
11Hearing- 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)
12Hearing- 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 -
13Presbycusis
- 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
14Hearing- 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
15Equilibrium- 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
16Equilibrium- 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
17Equilibrium- 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 -
-
-
18Equilibrium- 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
19Equilibrium- 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.) -
20Equilibrium- 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
21Equilibrium- 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
22Equilibrium- 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.
23SIB Evaluation/Survey
- For Bev Hartley (whoever that is), ONLY provide
comments if you saw her this year
Have a Nice Weekend!