Report on Audition

1. **The Inner ear

2. Cochlea - main structure
-liquid filled
- liquid is set into vibration by the
movement of the stapes against the
o oval window
Upper part – scala vestibule
Lower part- scala tympani
Organ of Corti- large structure in the cochlear
partition
two
separated by
cochlear
partition

3. Main structures
Hair cells- Bending of cilia in the inner hair
cells are responsible for transduction.
2 types of hair cells
inner hair cells- 3,500- bends, and does
transduction process.
outer hair cells- 12,000- increase the
vibration of the basilar
membrane

4. Basilar membrane- supports the organ of corti
and vibrates in response to sound
Tectorial membrane- extends over the hair
cells

5. Why inner hair cell bends?
Ans: because the in and out movement of the stapes creates
pressure changes in the liquid inside the cochlea that sets the
cochlear partition into up and down motion

6. Movement in one direction of the cilia 
opens channel in the membrane ions
flow into the cell
Movement opposite of that direction  ion
channels close no electrical signals generated
** we have low threshold for hearing
Video Clip

7. Q: how do we perceive pitch?
Bekesy’s Place Theory of Hearing-
frequency of a sound us indicated by the place
along the cochlea at which nerve firing is
highest.
Low frequency- maximum activity in the in
the hair cells and auditory nerve fibers at the
apex end of the basilar membrane
High frequency- cause maximum activity in
hair cells and auditory nerve fibers at the base
of the membrane.

8. Tonotropic map- an orderly map of
frequencies along the length of the cochlea.
Frequency tuning curve- This curve is
determined by presenting pure tones of
different frequencies and measuring how many
decibels are necessary to cause the neuron to
fire. This decibel level is the threshold for that
frequency
characteristic frequency- frequency to
which the neuron is most sensitive
Auditory masking- ability to hear a sound is
decrease by the presence of other sounds

9. Q: Why does the basilar membrane
vibrate more sharply in healthy cochleas?
The outer hair cells expand and contract in response to the
vibration of the basilar membrane, and this expansion and
contraction, whichonly occurs in live cochleas, amplifies and
sharpens the vibration of the basilar membrane.
**Cochlear amplifier

10. Frequency- is signaled by which fibers in the
cochlea fire to a tone as well as how the fibers
are fired.
Phase locking- property of firing at the same
place in the sound stimulus
Temporal coding- connection between the
frequency of the sound stimulus and the timing
of the auditory nerve firing; measurements of
the pattern of firing for auditory nerve fibers
indicate that phase locking occurs up to a
frequency of about 4,000 Hz.

11. Causes of hearing loss
• Conductive hearing loss- Blockage of sound
from reaching the receptors
• sensorineural hearing loss
-Damage to the hair cells
-Damage to the auditory nerve or the brain
Presbycusis- caused by old age
- Greatest at higher frequencies
-Prevalent on males than
females

12. • Noise-induced Hearing loss
-Occurs when loud noises cause
degeneration of the hair cells.
-damage to the organ of corti

13. WHERE AND WHAT STREAM
** a 45-year-old man with temporal lobe
damage caused by a head injury
** a 64-year-old woman with parietal and
frontal lobe damage caused by a stroke

14. Pathway of the Cochlea to the cortex
Inner hair cells
Auditory receiving area
in the cortex
Cochlear Nucleus Super Olivary Nucleus
Inferior
colliculus
Medial
Geniculate
Nucleus
Auditory receiving area
(A1)
Temporal lobe of the
Cortex

16. Cortical Processing

17. PITCH AND THE BRAIN
• Tonotropic map in the monkey cortex shows
that neurons that respond best to low
frequencies are located to the left, and
neurons that respond best to higher
frequencies are located to the right
• Studies found neurons in the brain that
respond to both pure tones and complex
tones that differ in ther harmonics but have
the same pitch
***Auditory cortex indeed is important
for the perception of pitch

18. Experience dependent plasticity in the
auditory system shows that in training
that involves a particular frequency,
increases in the space devoted to that
frequency in A1 is evident.