Hearing and Balance
Sound
The decibel (dB) is a
logarithmic unit of
measurement that
expresses the magnitude
of a physical quantity,
in this case sound.
It is dimensionless and is
the difference between
the log of the measured
sound and the log of a
reference sound.
Sound
Max 120 dB
France: Limited to 100 dB
http://vancouver.ca/engsvcs/projects/soundsmart/images/dbScale2-2-2.jpg
Sound Range
Middle C on a piano is: ~256 Hz
http://www.diracdelta.co.uk/science/source/h/e/hearing range in animals/image001.jpg
Figure 10-17
Ears
Ear Drum
From the ear there is a short canal that leads to the ear drum,
a thin membrane. closing off the canal. This membrane can be
easily damaged but has the ability to repair itself.
The canal also secretes an acidic wax that is used to collect dust
and other particles and also acts as a bactericide and fungicide.
http://www.1800endoscope.com/images/eardrum.jpg
Middle Ear
http://www.phon.ox.ac.uk/~jcoleman/middle_ear.GIF
http://media-2.web.britannica.com/eb-media/03/14303-004-A1009028.gif
Figure 10-20 (2 of 8)
Figure 10-20 (3 of 8)
Perilymph (cytoplasm like)
Endolymph (plasma like)
Figure 10-20 (4 of 8)
Figure 10-19, step 1
Figure 10-19, step 2
Figure 10-19, step 3
Figure 10-19, step 4
Figure 10-19, step 5
Figure 10-19, step 6
Figure 10-20 (6 of 8)
Outer Cells
Inner Cells
The outer cells respond by vibrating at the given frequency resulting
in a amplification of the sound. The inner cells are responsible for
transmitting the information.
10,000 to 20,000 hair cells. Can be killed by loud sounds
Figure 10-20 (8 of 8)
Figure 10-20 (7 of 8)
Bending of the stereocilium results in mechanically gated ion
channels to open. This causes changes in K and Na ions which
in turn cases voltage gated Ca channels to open.
Figure 10-21a
Figure 10-21b
Figure 10-22a
http://www.hearingaids4less.com/images/cochlea1.gif
Figure 10-22a
Figure 10-23a
Orientation of Canals
http://scienceblogs.com/afarensis/2006/05/16/bipedal_locomotion_and_semicir/
The Utricle and saccule respond to linear acceleration
(turning your head left or right, for example) and the
orientation of the head relative to gravity (tilting your head
left or right for example).
Utricle: Horizontal
Saccule: Vertical
The semicircular canals respond to angular accelerations.
The horizontal semicircular allows you to keep your gaze
fixed on an object while your head is moving (trying to read
a sign in a moving car for example).
Figure 10-23b
Figure 10-23c
Dizziness
1.
2.
3.
4.
5.
6.
Sit on a swivel chair blindfolded.
Turn the chair in one direction at a constant speed.
Stop the chair suddenly.
Remove blindfold.
Ask, which direction is the chair moving.
Observe eyes, not erratic eye movements.
Dizziness can be caused by inconsistent
information coming from the ears
and eyes.
Drunkenness may be partly caused by
buoyancy changes in the endolymph
resulting in changes to the capula.
Utricle: Horizontal
Saccule: Vertical
Figure 10-23d
The crystal are made from
calcium carbonate and
slide on a gelatinous
substrate.
Figure 10-23d
Figure 10-25 - Overview