1. Chapter 8 Special Senses

2. The Ear Houses two senses Receptors Hearing Equilibrium (balance)
Sound receptors
Mechanoreceptors
Both stimulated by the movement of fluid

3. Anatomy of the Ear The ear is divided into three major areas
Outer (external) ear
Middle ear
Inner (internal) ear

4. Outer (external) Ear Involved in hearing only
Structures of the external ear
Pinna (auricle)
External auditory canal

5. The External Auditory Canal
Short, narrow chamber in the temporal bone of the skull
Lined with skin
Ceruminous (wax) glands are present that secrete earwax or cerumen
Sound waves entering the canal eventually hit the tympanic membrane or eardrum and cause it to vibrate
Canal ends at the eardrum, which separates the outer from the middle ear

6. The Middle Ear or Tympanic Cavity
Air-filled cavity within the temporal bone
Only involved in the sense of hearing
Pharyngotympanic (auditory) tube
Runs obliquely downward to link the middle ear cavity with the throat
Allows for equalizing pressure during yawning or swallowing
Tube is otherwise collapsed

7. Bones of the Tympanic Cavity
3 of the smallest bones in the body span the cavity (ossicles)
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)

8. Bones of the Tympanic Cavity
Vibrations from the eardrum moves the malleus
These 3 bones transfer sound to the inner ear

9. Inner Ear or Bony Labyrinth
A maze of bony chambers within the temporal bone
Cochlea
Vestibule
Semicircular canals

10. Inner Ear or Bony Labyrinth
Includes sense organs for hearing & balance
Filled with perilymph

11. Mechanism of Equilibrium
Equilibrium has two functional parts
Static equilibrium
Receptors in the vestibule
Dynamic equilibrium
Receptors in the semicircular canals

12. Static Equilibrium Maculae – receptors within the vestibule
Report on the position of the head with respect to the pull of gravity when the body is not moving (static = rest)
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  sends impulses along the vestibular nerve to the cerebellum of the brain

13. Function of Maculae

14. Dynamic Equilibrium
Responds to angular or rotatory movements of the head
Crista ampullaris – receptors found within the semicircular canals
Tuft of hair cells are covered with a gelatinous cap called the cupula

15. Dynamic Equilibrium During angular head movements
The cupula stimulates the hair cells
An impulse is sent via the vestibular nerve to the cerebellum

16. Mechanism of Hearing Organ of Corti Located within the cochlea
Hearing 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

17. Hearing- Anatomy of the Cochlea

18. Mechanisms of Hearing
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

19. Chemical Senses: Taste & Smell
Both senses use chemoreceptors
Stimulated by chemicals in solution
5 types of taste receptors
Smell (olfactory) receptors
Sensitive to a much wider range of chemicals
Receptors for both senses complement each other and respond to many of the same stimuli

20. Olfaction – The Sense of Smell
Olfactory receptors are in the roof of each nasal cavity
Neurons with long cilia (olfactory hairs)
Chemicals must be dissolved in mucus for detection
Impulses are transmitted via the olfactory nerve
Interpretation of smells is made in the olfactory cortex of the brain

21. Olfactory Epithelium

22. The Sense of Taste
Taste receptors  Taste buds (Widely scattered throughout the oral cavity)
Location of taste buds
Most are on the tongue
Soft palate
Inner surface of the cheeks

23. The Tongue and Taste
The tongue is covered with 3 types of projections called papillae
Sharp or Filiform papillae – 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

24. Structure of Taste Buds
Gustatory cells
Have gustatory hairs (long microvilli)
Hairs are stimulated by chemicals dissolved in saliva and transmit impulses to the brain

25. Structure of Taste Buds
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

26. Anatomy of Taste Buds

27. Taste Sensations Sweet receptors Sour receptors Bitter receptors
Sugars
Saccharine
Some amino acids
Sour receptors
Acids
Bitter receptors
Alkaloids
Salty receptors
Metal ions
Umami
Glutamate- “Beef taste” of steak

28. Reasons not to get your tongue pierced…
Chipped or broken teeth
Infection
And possibly death

29. Girl who almost died from a brain abscess following a tongue piercing
She had part of her skull removed to relieve pressure caused by the infection
She can still feel the soft spot where the skull is missing
Rare, but real

30. Reasons not to get your tongue pierced…
Blood loss
The tongue contains large blood vessels, and you're in trouble if one of them is perforated. You could end up having to have the vessel closed surgically in hospital.
There is also the possibility of hitting and damaging a nerve
Imagine life with a tongue that doesn't work properly!
Lingering pain
Cases of neuralgia  - severe, long-lasting nerve pain
Hepatitis or HIV
Unsterile instruments are a great way to spread these and other infections

31. Still not convinced?
If you must do this, be sure to go to a reputable clinic, and be very sure that they do things properly: autoclave sterilization and gloves.
As we had tried to teach you with tattooing, be a smart consumer! 

32. Extra slides…

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

34. Tonsils

36. Middle Ear Infections website website use of tubes
Normal slight severe ear infection

37. Tubes for Middle Ear infections
How Are Ear Tubes Inserted?
Ear tubes are inserted through an outpatient surgical procedure called a myringotomy. A myringotomy refers to an incision (a hole) in the ear drum or tympanic membrane. This is most often done under a surgical microscope with a small scalpel (tiny knife), but it can also be accomplished with a laser.  If an ear tube is not inserted, the hole would heal and close within a few days. To prevent this, an ear tube is placed in the hole to keep it open and allow air to reach the middle ear space (ventilation).
Ear Tube Surgery  A light general anesthetic (laughing gas) is administered for young children. Some older children and adults may be able to tolerate the procedure without anesthetic. A myringotomy is performed and the fluid behind the ear drum (in the middle ear space) is suctioned out. The ear tube is then placed in the hole. Ear drops may be administered after the ear tube is placed and may be necessary for a few days. The procedure usually lasts less than 15 minutes and patients awaken quickly. Sometimes the otolaryngologist will recommend removal of the adenoid tissue (lymph tissue located in the upper airway behind the nose) when ear tubes are placed.  This is often considered when a repeat tube insertion is necessary. Current research indicates that removing adenoid tissue concurrent with placement of ear tubes can reduce the risk of recurrent ear infection and the need for repeat surgery.

38. Ear Disorders
Vertigo-website
Tinnitus-website

39. Adaptation and Threshold for Taste and Smell
Adaptation: decreasing sensitivity
Threshold: minimal amount of stimulus needed to illicit a response.
Taste:
Adapt: complete 1-5 minutes
Threshold: bitter lowest (poisons), sour, salt & sweet
Smell:
Adapt: 50% after 1 sec.
Threshold: very low 1/25,000,000,000mg/ml.