2. The Central Nervous System
•The central nervous system
contains
•the brain
•the spinal cord
•The average adult brain weighs
about 3 pounds
•The brain contains about 100
billion neurons that transmit
information about our bodies up to
our brains, where that information
is processed
Image from: faculty.washington.edu
3. The Brain
Image from: faculty.vassar.edu
•Our brains are divided
into four lobes:
•Frontal
•Temporal
•Parietal
•Occipital
•The temporal lobe is
where auditory
information is sent to be
processed
4. The Skull
Our brains are
protected by
our skull
The structures
of the ear are
housed in the
temporal
bone
Image from: cnx.org
5. Important Anatomy Terms to Know
External vs. Internal Auditory Canal
Afferent vs. Efferent
Ipsilateral vs. Contralateral
6. External vs. Internal Auditory Canal
You know that the EAC is part of the outer ear
The internal auditory canal (IAC) or internal auditory
meatus is an opening in the temporal bone where the
facial nerve (CN VII) and auditory nerve (CN VIII)
travel to the brainstem
7. Afferent vs. Efferent
Afferent refers to the ascending pathway of sensory
information that travels from our peripheral system to our
central system. Another way to think about this is the
transmission of information about all of our senses up to
our brain. (i.e. when you touch a hot pan, the afferent
nervous system sends the pain signal to your brain)
Afferent =“up, up, and away”
Efferent refers to the descending pathway of information
from our brain to a part of our body. (i.e. after your brain
receives the pain signal from touching the hot pan, an
efferent message is sent to your hand to pull away from the
pan)
8. Ipsilateral vs. Contralateral
Ipsilateral = same side
Contralateral = opposite side
Examples:
When using nasal spray in the right nostril, you should
point the tip of the nasal spray at the corner of the
ipsilateral (right) eye
During audiometric testing of the right ear, you present
masking noise to the contralateral ear (left ear in this
case) in order to isolate the test ear.
9.
10. So what happens to sound after it
reaches the cochlea?
Most of our auditory system is AFFERENT
Sound travels from our cochlea UP:
to the auditory nerve, then
To the brainstem, then
To the brain (where it is perceived as sound)
Information from one ear, reaches both sides of the
brain
Our PRIMARY auditory cortex is usually located in the
left hemisphere, as are our primary speech centers
13. Efferent Auditory Pathways
Descending nerve fibers from the auditory cortex (brain) to
the brainstem and cochlea
The auditory efferent system is not well understood and
remains somewhat of a mystery
Our auditory efferent system is responsible for:
Sending inhibitory messages to the outer hair cells in the
cochlea to control stiffness and membrane vibration
Innervation of the stapedius and tensor tympani muscles in
the middle ear
Our efferent system is believed to play a role in:
detection of signals in noise, protection in noise-induced
cochlear damage, development of hearing and processing of
complex auditory signals
15. Central Auditory Processes
Our central auditory system is responsible for the following
auditory processes:
Sound localization and lateralization
Auditory discrimination
Determining the difference between different speech sounds
Auditory pattern recognition
i.e. identifying a melody
Temporal (timing) aspects of hearing
Temporal integration
Temporal discrimination (e.g., temporal gap detection)
Temporal ordering
Temporal masking
Auditory performance in competing acoustic signals
Auditory performance with degraded acoustic signals
ASHA, 1995
