1. www.soran.edu.iq Physiology Behrouz Mahmoudi Hearing System 1

2. www.soran.edu.iq The Outer Ear Consists of: The Pinna - cartilaginous, highly variable in appearance, some landmarks. External Auditory Canal (or external auditory meatus) - 2.5 cm tube. 2

3. www.soran.edu.iq Pinna Landmarks Helix Antihelix Concha Tragus Intertragal Notch Antitragus 3

4. www.soran.edu.iq External Auditory Canal lateral portion-cartilage medial portion-osseous lined with epidermal (skin) tissue hairs in lateral part cerumen (ear wax) secreted in lateral part. 4

5. www.soran.edu.iq Outer Ear Functions Amplification / Filtering Protection Localization 5

6. www.soran.edu.iq The Middle Ear: A cleft within the temporal bone Lining is mucous membrane Tympanic Membrane separates it from EAC Eustachian tube connects it to nasopharynx Also Connected to Mastoid Air Cells 6

7. www.soran.edu.iq Middle Ear Structures 1- Malleus 2- Incus --Ossicles 3- Stapes 4- Tympanic Membrane (Eardrum) 5- Round Window 6- Eustachian Tube 7

8. www.soran.edu.iq Middle Ear Muscles 1. The Stapedius Attaches to Stapes,Contracts in Response to Loud sounds, chewing, speaking; Facial (VIIth cranial) nerve 2. The Tensor Tympani Helps open Eustachian tube 8

9. www.soran.edu.iq Middle Ear Functions Impedance Matching Filtering Acoustic Reflex 9

10. www.soran.edu.iq These sounds get through the middle ear most readily 10

11. www.soran.edu.iq 11

12. www.soran.edu.iq Two Halves: Vestibular--transduces motion and pull of gravity Cochlear--transduces sound energy (Both use Hair Cells) INNER EAR 12

13. www.soran.edu.iq The Stereocilia on IHCs and OHCs OHCs (at top) V or W shaped ranks IHC (at bottom) straight line ranks 13

14. www.soran.edu.iq Cochlear Functions Transduction- Converting acoustical- mechanical energy into electro-chemical energy. Frequency Analysis-Breaking sound up into its component frequencies – Bekesy’s Traveling Wave – Active Tuning from OHCs 14

15. www.soran.edu.iq Afferent Afferent & Efferent Neurons 15

16. www.soran.edu.iq IHC activation alters firing rate 16

17. www.soran.edu.iq Major Components of the Central Auditory Nervous System (CANS) VIIIth cranial nerve Cochlear Nucleus Superior Olivary Complex Lateral Lemniscus Inferior Colliculus Medial Geniculate Body Primary Auditory Cortex Brainstem Thalamus Mid-brain Temporal Lobe 17

18. www.soran.edu.iq Mid-Saggital View of Brain Pons Cerebellum 4th Ventricle Thalamus Corpus Callosum 18

19. www.soran.edu.iq Cortical Processing Pattern Recognition Duration Discrimination Localization of Sounds Selective Attention 19

20. www.soran.edu.iq Cerebral Dominance/Laterality Language Processing in the left hemisphere. (Remember the right ear has the strongest connections to the left hemisphere) Most people show a right-ear advantage in processing linguistic stimuli 20