1. Cranial Nerves (overview)
• Cranial Nerves
There are two primary
function/groups of the nervous
system. They are:
1. Motor cranial nerves
2. Sensory cranial nerves

2. Cranial Nerves (overview)
• Cranial Nerves
Four of the twelve cranial nerves serve as
combined sensory and motor nerves. They
are:
1. The fifth
2. The seventh
3. The ninth
4. The tenth

3. Cranial Nerves (overview)
As you can see two of these four
combination cranial nerves affect
auditory information.
The fifth which controls the tensor
tympani muscle and the seventh
which controls the stapedial muscle.

4. Cranial Nerves (overview)
• Cranial Nerves—motor
There are five dedicated motor nerves (not
combination). They are:
1. The third
2. The fourth
3. The sixth
4. The eleventh
5. The twelfth

5. Cranial Nerves (overview)
• Cranial Nerves—sensory
There are only three sensory—not
combination—nerves. They are:
1. The first (smell)
2. The second (vision)
3. The eighth (auditory)

6. Cranial Nerves (overview)
• Cranial Nerves
The fifth (trigeminal), seventh (facial),
and of course eighth (acoustic)
cranial nerves are important to the
healthy functions of audition.

7. Cranial Nerves (overview)
• Afferent—Efferent & Reflexes
Tensor/tympani and Stapedial
muscles are controlled by both the
afferent information received by the
brain and the efferent synapse sent to
the motor unit (muscles).

8. Cranial Nerves (overview)
Specific knowledge of reflex results
will assist in programming the output
of digital hearing instruments.

9. Cranial Nerves (overview)
• Tympanometry and Ipsilateral reflexes
Ipsilateral reflex results are recorded in
SPL. This number will directly translate
into hearing instrument programming as
all hearing instrument output performance
information is recorded in SPL—not HL.

10. Cranial Nerves (overview)
• Tympanometry and Ipsilateral Reflexes
When reflexes are found to be different
between ears, careful programming
considerations must be made. The
recorded acoustic reflex will be the exact
output level where the hearing instrument
will influence normal physiological
(afferent/efferent) processes.