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

Hearing 12/10/1439

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

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

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

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

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

Hering pathway 12/10/1439 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 hear sound . 12/10/1439

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