1. 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
12/10/1439

2. Hearing
12/10/1439

3. these vibrationa are transmitted to the Middle Ear .
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 .
these vibrationa are transmitted to the Middle Ear .
12/10/1439

4. 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 .
12/10/1439

5. The Middle Ear ( Contd )
12/10/1439
Figure 17.21

6. C/ Inner Ear Membranous labyrinth contains endolymph
Bony labyrinth surrounds and protects membranous labyrinth
Cochlea
Cochlea القوقعة contains the receptors for hearing
C/ Inner Ear
12/10/1439

7. 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 ) .
12/10/1439

8. Hering pathway
12/10/1439
Figure 17.29

9. 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 hear sound .
12/10/1439

10. 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.
12/10/1439