Chapter 17, part 3

1. Chapter 17, part 3 The Special Senses

2. SECTION 17-4Equilibrium and Hearing

3. Both equilibrium and hearing are provided by receptors of the inner ear Anatomy of the ear – External Ear • Auricle or pinnae surrounds the ear • External acoustic meatus ends on tympanic membrane

4. Figure 17.20 The Anatomy of the Ear Figure 17.20

5. Middle ear • Communicates with pharynx via pharyngotympanic membrane • Middle ear encloses and protects the auditory ossicles

6. Figure 17.21 The Middle Ear Figure 17.21

7. Inner ear • Membranous labyrinth contains endolymph • Bony labyrinth surrounds and protects membranous labyrinth • Vestibule • Semicircular canals • Cochlea

8. Figure 17.22 The Inner Ear Figure 17.22

9. Components of the inner ear • Vestibule contains the utricle and saccule • Semicircular canals contain the semicircular ducts • Cochlea contains the cochlear duct

10. Windows • Round window separates the perilymph from the air spaces of the middle ear • Oval window connected to the base of the stapes • Basic receptors of inner ear are hair cells • Provide information about the direction and strength of stimuli

11. Equilibrium • Anterior, posterior and lateral semicircular ducts are continuous with the utricle • Each duct contains an ampulla with a gelatinous cupula and associated sensory receptor • Saccule and utricle connected by a passageway continuous with the endolymphatic duct • Terminates in the endolymphatic sac • Saccule and utricle have hair cells clustered in maculae • Cilia contact the otolith (statoconia)

12. Figure 17.23 The Vestibular Complex Figure 17.23a, b, & d

13. Figure 17.23 The Vestibular Complex Figure 17.23c

14. Figure 17.23 The Vestibular Complex Figure 17.23e

15. Vestibular neural pathway • Vestibular receptors activate sensory neurons of the vestibular ganglia • Axons form the vestibular branch of cranial nerve VII • Synapses within the vestibular nuclei

16. Figure 17.24 Pathways for Equilibrium Sensation Figure 17.24

17. Hearing • Cochlear duct lies between the vestibular duct and the tympanic duct • Hair cells of the cochlear duct lie within the Organ of Corti • Intensity is the energy content of a sound • Measured in decibels

18. Figure 17.25 The Cochlea Figure 17.25a, b

19. Figure 17.26 The Organ Of Corti Figure 17.26a, b

20. Pathway of sound • Sound waves travel toward tympanic membrane, which vibrates • Auditory ossicles conduct the vibration into the inner ear • Tensor tympani and stapedius muscles contract to reduce the amount of movement when loud sounds arrive • Movement at the oval window applies pressure to the perilymph of the cochlear duct • Pressure waves distort basilar membrane • Hair cells of the Organ of Corti are pushed against the tectoral membrane

21. Figure 17.28 Sound and Hearing Figure 17.28a

22. Figure 17.29 Sound and Hearing Figure 17.29

23. Neural pathway • Sensory neurons of hearing are located in the spiral ganglion of the cochlea • Afferent fibers form the cochlear branch of cranial nerve VIII • Synapse at the cochlear nucleus

24. 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 equilibrium and hearing. • The pathways for the sensations of equilibrium and hearing.