2. “If a tree falls…” If a tree falls in the forest and there is nobody around to hear it… Does it make a noise? NO…Sound (like colour) is all in your head!

3. Hearing What is Sound? Compression & Rarefaction of air molecules.

4. Sound Waves Amplitude (Loudness) Strength or height of the wave Frequency (Pitch) Distance twixt consecutive peaks Mix (Timbre) Interaction of different waves 1 Hertz = 1 Cycle/Sec Human Hearing 20 - 20k Hz

5. Perceiving Pitch Georg von Békésy 1899-1972 Place Theory - pitch determined by point of maximal vibration on basilar membrane Traveling Wave Theory 1957 Frequency Theory - pitch determined by the rate at which the hair cells fire (i.e., 1KHz tone cause hair cells to fire 1k times/sec) Volley Principle Volley Principle

6. The Ear  Houses two senses  Hearing  Equilibrium (balance)  Receptors are mechanoreceptors

7. Anatomy of the Ear Slide 8.21  The ear is divided into three areas  Outer (external) ear  Middle ear  Inner ear Figure 8.12

8. The External Ear Slide 8.22  Involved in hearing only  Structures of the external ear  Pinna (auricle)  External auditory canal Figure 8.12

9. The External Auditory Canal Slide 8.23  Narrow chamber in the temporal bone  Lined with skin  Ceruminous (wax) glands are present  Ends at the tympanic membrane

10. malleus cochlea incus pinna auditory canal tympanic membrane auditory/8th nerve Outer Ear Tympanic Membrane Tympanic Membrane - collect “sound” & vibrate ossicles Pinna Pinna - collect and direct “sound” into auditory canal Auditory Canal Auditory Canal - amplify & funnel “sound” to tympanic membrane

11. The Middle Ear or Tympanic Cavity Slide 8.24a  Air-filled cavity within the temporal bone  Only involved in the sense of hearing

12. Middle Ear Malleus Malleus - vibrate & move the Incus Incus Incus - vibrate & move the Stapes Stapes Stapes - vibrate against Oval Window of Cochlea malleusincus handle of malleus long process of incus stapes

13. The Middle Ear or Tympanic Cavity Slide 8.24b  Two tubes are associated with the inner ear  The opening from the auditory canal is covered by the tympanic membrane  The auditory tube connecting the middle ear with the throat  Allows for equalizing pressure during yawning or swallowing  This tube is otherwise collapsed

14. Bones of the Tympanic Cavity Slide 8.25a  Three bones span the cavity  Malleus (hammer)  Incus (anvil)  Stapes (stirrip) Figure 8.12

15. Bones of the Tympanic Cavity Slide 8.25b  Vibrations from eardrum move the malleus  These bones transfer sound to the inner ear Figure 8.12

16. Inner Ear or Bony Labyrinth Slide 8.26a  Includes sense organs for hearing and balance  Filled with perilymph Figure 8.12

17. Inner Ear or Bony Labrynth Slide 8.26b  A maze of bony chambers within the temporal bone  Cochlea  Vestibule  Semicircular canals

18. Inner Ear lateral semicircular canal posterior semicircular canal vestibule anterior semicircuar canal cochlea Cochlea Cochlea - filled with fluid & contains receptors (Hair Cells) for hearing (Hair Cells) Basilar Membrane Basilar Membrane - divides length of cochlea & holds the hair cells

19. Auditory Pathway

20. Organs of Hearing Slide 8.27a  Organ of Corti  Located within the cochlea  Receptors = hair cells on the basilar membrane  Gel-like tectorial membrane is capable of bending hair cells  Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

21. Organs of Hearing Slide 8.27b

22. Mechanisms of Hearing Slide 8.28  Vibrations from sound waves move tectorial membrane  Hair cells are bent by the membrane  An action potential starts in the cochlear nerve  Continued stimulation can lead to adaptation

23. Mechanisms of Hearing Slide 8.29 Figure 8.14

24. Organs of Equilibrium Slide 8.30a  Receptor cells are in two structures  Vestibule  Semicircular canals Figure 8.16a, b

25. Organs of Equilibrium Slide 8.30b  Equilibrium has two functional parts  Static equilibrium – sense of gravity at rest  Dynamic equilibrium – angular and rotary head movements Figure 8.16a, b

26. Static Equilibrium Slide 8.31  Maculae – receptors in the vestibule  Report on the position of the head  Send information via the vestibular nerve  Anatomy of the maculae  Hair cells are embedded in the otolithic membrane  Otoliths (tiny stones) float in a gel around the hair cells  Movements cause otoliths to bend the hair cells

27. Function of Maculae Slide 8.32 Figure 8.15

28. Dynamic Equilibrium Slide 8.33a  Crista ampullaris – receptors in the semicircular canals  Tuft of hair cells  Cupula (gelatinous cap) covers the hair cells Figure 8.16c

29. Dynamic Equilibrium Slide 8.33b  Action of angular head movements  The cupula stimulates the hair cells  An impulse is sent via the vestibular nerve to the cerebellum Figure 8.16c

32. Chemical Senses – Taste and Smell Slide 8.34  Both senses use chemoreceptors  Stimulated by chemicals in solution  Taste has four types of receptors  Smell can differentiate a large range of chemicals  Both senses complement each other and respond to many of the same stimuli

33. Olfaction – The Sense of Smell Slide 8.35  Olfactory receptors are in the roof of the nasal cavity  Neurons with long cilia  Chemicals must be dissolved in mucus for detection  Impulses are transmitted via the olfactory nerve  Interpretation of smells is made in the cortex

34. Olfactory Epithelium Slide 8.36 Figure 8.17

35. The Sense of Taste Slide 8.37  Taste buds house the receptor organs  Location of taste buds  Most are on the tongue  Soft palate  Cheeks Figure 8.18a, b

36. Structure of Taste Buds Slide 8.39a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Gustatory cells are the receptors  Have gustatory hairs (long microvilli)  Hairs are stimulated by chemicals dissolved in saliva

37. Structure of Taste Buds Slide 8.39b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas  Facial nerve  Glossopharyngeal nerve  Vagus nerve

38. Anatomy of Taste Buds Slide 8.40 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.18

39. Taste Sensations Slide 8.41 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Sweet receptors  Sugars  Saccharine  Some amino acids  Sour receptors  Acids  Bitter receptors  Alkaloids  Salty receptors  Metal ions

40. Developmental Aspects of the Special Senses Slide 8.42 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Formed early in embryonic development  Eyes are outgrowths of the brain  All special senses are functional at birth