1. Organs of Hearing 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 is attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

2. Organs of Hearing
Figure 8.15

3. Mechanisms of Hearing
Figure 8.16a–b

4. The Process of Hearing
1) Vibrations from sound waves move through a medium to the Pinna and into the auditory canal of the outer ear.
2) The vibrations reach the middle ear and vibrate the eardrum. The malleus bone which is attached to the eardrum is vibrated and it is sent to the incus and to the stapes bones.
3) The vibrations are amplified as they travel through the three bones
4) The stapes is attached to the cochlea at the oval window of the inner ear and it vibrates the fluid inside called endolymph.

5. The Process of Hearing
5) In the Cochlea the Organ of Corti has hair (receptor) cells touching the tectorial membrane
6) The hair cells are bent by the membrane and an action potential starts in the cochlear nerve sending signals to the auditory cortex.
7) Continued stimulation can lead to adaptation Ex: like tuning out the furnace in the room

6. Homeostatic Imbalances
Conduction Deafness – some kind of interference with the conduction of sound vibrations to the fluids of the inner ear (could be as simple as ear wax)
Otosclerosis – fusion of ossicle bones (hammer,
anvil, stirrup)
Hearing aides – can help overcome conduction
deafness; conducts sounds through the skull
Sensorineural Deafness – occurs from damage to the receptor cells in the Organ of Corti, cochlear nerve, or auditory cortex in the brain (nerve structures)
Often caused by exposure to loud noises (MUSIC, guns, jackhammer, etc.)

7. Organs of Equilibrium Receptor cells are in two structures
Vestibule 2) Semicircular canals
Figure 8.14a–b

8. Organs of Equilibrium Equilibrium has two functional parts
Static equilibrium (Vestibule) = body NOT moving
Dynamic equilibrium (Semi-circular canals) = body moving
Figure 8.14a–b

9. Static Equilibrium and Functon of Maculae
Maculae – receptors in the vestibule that report on the position of the head
Sends info to the cerebellum via the vestibular nerve to help keep our head erect.
Anatomy of the maculae
Hair cells are embedded in the otolithic membrane which is a jelly-like material containing Otoliths
Otoliths (tiny calcium stones) float in a gel around the hair cells
Movements due to changes in gravity cause otoliths to bend the hair cells … kind of messing with yourself when you headbang!

10. Function of Maculae
Figure 8.13a–b

11. Dynamic Equilibrium and function of Crista Ampullaris
Crista ampullaris – receptors in the semicircular canals with Tufts of hair cells
Cupula (gelatinous cap) covers the hair cells
Figure 8.14c

12. Dynamic Equilibrium and function of Crista Ampullaris
Action of angular head movements (Boat, roller coaster, merry-go-round)
1) The cupula stimulates the hair cells
2) An action potential is sent via the vestibular nerve to the cerebellum
3) Static and dynamic equilibrium have different receptors but they work together with many other receptors to keep your balance.
Figure 8.14c

13. Chemical Senses – Taste and Smell
Both senses use chemoreceptors and are stimulated by chemicals in solution
Both senses complement each other and respond to many of the same stimuli

14. Olfaction – The Sense of Smell
Olfactory receptors - Neurons with long cilia
in the roof of the nasal cavity
Chemicals must be dissolved in mucus for detection
Impulses are transmitted via the olfactory nerve
Interpretation of smells is made in the cortex
Olfactory pathways are tied to the limbic system (emotions). Certain smells bring back memories.

15. Olfactory Epithelium
Figure 8.17

16. The Sense of Taste Taste buds house the receptor organs for taste
Most are on the tongue and some are on the soft palate and Cheeks
Figure 8.18a–b

17. The Tongue and Taste
The tongue is covered with projections called papillae
Filiform papillae – sharp with no taste buds
Fungifiorm papillae – rounded with taste buds
Circumvallate papillae – large papillae with taste buds
Taste buds are found on the sides of papillae

18. Structure of Taste Buds
Gustatory cells – taste receptors with gustatory hairs (long microvilli)
Hairs are stimulated by chemicals dissolved in saliva

19. Structure of Taste Buds
Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas
1) Facial nerve 2) Glossopharyngeal nerve
3) Vagus nerve

20. Anatomy of Taste Buds
Figure 8.18

21. Taste Sensations
Sweet receptors : Sugars, Saccharine, Some amino acids
Sour receptors : Acids
Bitter receptors: Alkaloids (bases)
Salty receptors: Metal ions
Umami: amino acid glutamate; “beef taste” of steak located in the pharynx

22. Developmental Aspects of the Special Senses
Formed early in embryonic development
Eyes are outgrowths of the brain
All special senses are functional at birth