April 21, 2014 – Hearing and equilibrium 1. What is sound and how is it perceived?

1. April 21, 2014 – Hearing and equilibrium • 1. What is sound and how is it perceived? • 2. Functional anatomy of the mammalian (human) ear. • 3. Distinguishing volume and pitch • 4. Other modes of animal hearing • 5. Ears and equilibrium in mammals • 6. Equilibrium in other critters

2. What is sound?

3. Captures and funnels sound to tympanic membrane

4. Townsend's big-eared bat (Corynorhinus townsendii) Harbor seal (Phoca vitulina)

5. Amplifies sound and transfers energy the oval window

6. Hearing- Mammals (con’t) • Pathway: • Sound waves in air travel through outer ear until they reach tympanic membrane • Sound waves vibrate membrane, which in turn vibrates 3 bones of middle ear: Malleus Incus Stapes (outin: “MIS”)

7. Hearing- Mammals (con’t) • Pathway: • Stapes transmits sound to the oval window -membrane on the surface of cochlea

8. Detects sound frequency transmits signal to the auditory nerve

9. Hearing- Mammals (con’t) • Pathway: • Stapes transmits sound to the oval window -membrane on the surface of cochlea • Vibration on oval window causes vibration of perilymph (fluid) in the cochlea

11. Side view of uncurled Cochlea

12. Vestibular canal Cochlear duct Tectorial membrane Hair cells Axons of sensory neurons Tympanic canal

14. Hair cells

16. Hearing- Mammals (con’t) • Two Components of Sound Wave: There are two main components of the sound wave that are detected and used by the auditory system: • Volume- Amplitude (height of wave) • Pitch or Frequency • (no. of waves per unit time)

17. Hearing- Mammals (con’t) 1. Amplitude larger amplitude= louder sound -larger amplitude results in stronger pressure on the hair cells, more rapid firing of action potentials

18. Hearing- Mammals (con’t) 1. Amplitude larger amplitude= louder sound -larger amplitude results in stronger pressure on the hair cells, more rapid firing of action potentials 2. Pitch - basilar membrane varies in thickness and flexibility -base= narrow and stiff; stimulated by higher frequencies -tip (apex)= wider and more flexible; stimulated by lower frequenices

20. Cochlear animation • http://www.hhmi.org/biointeractive/cochlea

21. Age-related hearing loss is often associated with a reduced ability to hear high-pitched sounds. Propose a mechanism to explain this. Blackburnian Warbler (Setophaga fusca)

22. Cochlear implants Charles Limb TED talk: http://www.ted.com/talks/charles_limb_building_the_musical_muscle.html

23. Hearing in other vertebrates 1. Fish- have inner ear, but no tympanic membrane and no opening to outside -pathway: sound waves  skull inner ear  brain -inner ear has small calcium carbonate particles called otoliths -stimulating otolith stimulates connected hair cells 2. Amphibians -have tympanic membrane on outside surface of body -pathway: sound waves  tympanic membrane middle ear bone  inner ear  brain -single middle ear bone

24. Evolution of the vertebrate ear • Inner fish • http://www.pbs.org/your-inner-fish/interactives/explore-your-inner-animals/

25. Hearing- Invertebrates • Two main ways to detect sounds: 1. Hairs on body -vibrate in response to sound waves -vary in stiffness and length 2. Tympanic Membrane -thin sheet stretched across an internal air space -localized on different parts of the body -pathway: sound waves  tympanic membrane  connected nerves  brain

26. Equilibrium- Mammals • Organs to detect body position and maintain balance located in inner ear a. Utricle and Saccule (2 parts of same organ) -located next to oval window -detect which direction is up and detect body position and accleration b. Semicircular Canals (3 canals in total) -next to utricle -detect angular movements Semicircular Canals

27. 2. Pathway: • Utricle and saccule contain clusters of hair cells embedded in a gel called a cupula b. Cupulacontains otoliths c. Cupula(with otoliths) is heavier than the endolymph(fluid) in the utricle and saccule, so gravity is pulling the cupula down on to the hairs of the hair cells

28. 2. Pathway (con’t): d. Changes in angle of body (i.e. changes in position of head) change the force on the hair cells -causes stimulation of some cells that weren’t stimulated before -causes some to increase/decrease their signals

29. Equilibrium- Mammals Semicircular Canals 3. Semicircular Canals a. 3 canals (“loops”) -1 for each plane: side-to-side front and back up and down b. same mechanism of stimulation as for utricle and saccule (cupula with otoliths, hair cells, etc.)

30. Equilibrium- Aquatic Organisms Lateral Line System 1. Fish: lateral line on both sides of body a. series of mechanoreceptors called neuromasts on body just under the epidermis b. Small openings (pores) in epidermis allow for water to enter into lateral line canals

31. Equilibrium- Lateral Line (con’t) Lateral Line System • Water stimulates clusters of hair cells in the neuromasts by bending the cupula (gelatinous cap over the hair cells) d. Stimulation causes release of neurotransmitters, sending signals through sensory nerves to brain

32. Equilibrium- Invertebrates • Most invertebrates have sensory “organ” called statocysts a. Parts of statocyst: -layer of ciliated receptor cells surrounding an open chamber -inside chamber are 1+ grains of dense material called statoliths 2. Pathway: a. Gravity causes statoliths to settle downward b. Once reach bottom of chamber, stimulating cilia of receptor cells c. Stimulated cells release neurotransmitters, stimulating connecting sensory nerve fibers