The Ear: Hearing and Balance

1. The Ear: Hearing and Balance • The three parts of the ear are the inner, outer, and middle ear • outer and middle ear= hearing • inner ear= hearing and equilibrium • Receptors for hearing and balance: • Respond to separate stimuli • Are activated independently

2. The Ear: Hearing and Balance Figure 15.25a

3. Outer Ear • The auricle (pinna) is composed of: • The helix (rim) • The lobule (earlobe) • External auditory canal • Short, curved tube filled with ceruminous glands • Secretes cerumen (ear wax)

4. Outer Ear • Tympanic membrane (eardrum) • Boundary between outer and middle ears • Thin connective tissue membrane that vibrates in response to sound • Transfers sound energy to the middle ear ossicles

5. Middle Ear (Tympanic Cavity) • A small, air-filled, mucosa-lined cavity • Pharyngotympanic (auditory) tube – connects the middle ear to the nasopharynx • used to be called the eustachian tube • Equalizes pressure in the middle ear cavity with the external air pressure (i.e. ‘popping’ ears at changing altitudes)

6. Middle and Internal Ear Figure 15.25b

7. Ear Ossicles • The tympanic cavity contains three small bones: the malleus, incus, and stapes • Hammer, anvil, and stirrup • Transmit vibratory motion of the eardrum to the oval window

8. Ear Ossicles Figure 15.26

9. Chunk and Chew: • Partner A: • Please describe the function and anatomical parts of the outer ear. • Partner B: • Please describe the anatomical parts of the middle ear. How does sound travel here?

10. Inner Ear • Bony labyrinth • Channels worming their way through the temporal bone • Three regions: • Vestibule, cochlea, and semicircular canals • Membranous labyrinth • Series of membranous sacs within the bony labyrinth • Filled with a potassium-rich fluid

11. Inner Ear Figure 15.27

12. The Vestibule • The utricle (bottom section) extends into the semicircular canals • These sacs: • House equilibrium receptors called maculae • Respond to gravity and changes in the position of the head

13. The Semicircular Canals • Three canals that each define two-thirds of a circle and lie in the three planes of space • These receptors respond to angular movements of the head

14. The Cochlea • A spiral, conical, bony chamber that: • Contains the cochlear duct • Contains the organ of Corti (hearing receptor)-aides in processing pitch, frequency, etc.

15. Check it out! • https://www.youtube.com/watch?v=pCCcFDoyBxM

16. Sound and Mechanisms of Hearing • Sound vibrations beat against the eardrum • The eardrum pushes against the ossicles, which presses fluid in the inner ear against the oval and round windows • This movement sets up shearing forces that pull on hair cells • Moving hair cells stimulates the cochlear nerve that sends impulses to the brain

17. Lets look at how they work!!! • http://www.sumanasinc.com/webcontent/animations/content/soundtransduction.html

18. Properties of Sound • Frequency – the number of waves that pass a given point in a given time • Pitch – perception of different frequencies (we hear from 20–20,000 Hz)

19. Properties of Sound • Amplitude – intensity of a sound measured in decibels (dB) • Loudness – subjective interpretation of sound intensity Figure 15.29

20. Frequency and Amplitude Figure 15.30

21. Chunk and Chew: • Partner A: • Please explain to your partner the anatomical parts and functions of the inner ear. • Partner B: • Please describe the properties of sound…what aspect of waves do we hear? • Both partners: • Follow the path of sound from the outer ear to the cochlea.