Transcript Special Senses for Dental Students

Physiology of Vision & Hearing for Dental
Students
Lecture Copy
Dr Taha Sadig Ahmed
Medicine Bachelor & Bachelor of Surgery (
Khartoum University )
 PhD ( Bristol University , England )
 Membership of the American Association of
Neuromuscular & Electrodiagnostic Medicine
,AANEM ( USA )
 Consultant , Clinical Neurophysiology ,
King Abdulaziz University Hospital , Riyadh
 Associate Professor , College of Medicicne ,
Riyadh

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Hearing
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A/ ExternaL Ear
Starts from Pinna ( auricle ) which is the external part , and
ends at Tympanic Membrane .
the Pinna collects sound waves ( like a funnel ) and passes
them into the External Auditory Meatus
the External Auditory meatus transmits these sound waves 
to cause vibrations in the Tympanic Membrane .
03/07/1437vibrationa are transmitted to the Middle Ear .
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these
B/ Middle Ear
It is an air-filled
cavity .
Lies between
Tympanic
membrane and
Oval and Round
windows
Communicates
with pharynx via
Eustachean tube
Contains 3
auditory ossicles
(bones) , called
Malleus , Incus &
Stapes .
Contains tensor
tympani and
stapedius
muscles .
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The Middle Ear ( Contd )
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Figure 17.21
Membranous
labyrinth
contains
endolymph
Bony labyrinth
surrounds and
protects
membranous
labyrinth
– Cochlea
Cochlea ‫القوقعة‬
contains the
receptors for
hearing
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C/ Inner Ear
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The Organ of Corti is the receptor for
sound
The Cochlea contains a fluid called Perilymph .
The Organ of Corti inside the Cochlea is the
receptor for sound .
It is located ( resting ) on the Basilar membrane
Contains inner and outer hair cells .
Extends from the base to the apex of the
It contains hair cells which , when they vibrate ,
produce Action Potentials in the 8th Cranial Nerve (
Cochlear nerve ) .
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Figure 17.29
Sound Pathway
Sound waves travel toward tympanic membrane,
which vibrates
Auditory ossicles conduct the vibration into the
inner ear
Movement at the oval window applies pressure
to the perilymph of the cochlea
Pressure waves move hair cells in the Organ of
Corti
This leads to generation of Action Potentials in
the Cochlear nerve .
Cell-bodies of the Cochlear nerve are located in
the spiral ganglion of the cochlea
Their afferent fibers synapse in the Cochlear
Nucleus in the medulla  Inferior Colliculus 
Medial Geniculate Body  Temporal Lobe  we
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hear sound .
You should now be familiar with:
The sensory organs of smell, and the olfactory
pathways in the brain.
The accessory and internal structures of the eye,
and their functions.
How light stimulates the production of nerve
impulses, and the visual pathways.
The structures of the external and middle ear and
how they function.
The parts of the inner ear and their roles in hearing.
The pathways for the sensation of hearing.
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