Special Senses

1. Special Senses Utilize distinct receptor cells as receptors

2. Chemical senses • Taste (gustation) • Smell (olfaction)

3. Taste • Taste buds. • Most are on the tongue. • Papillae. • Filiform - rough, conical shape, few taste buds • Fungiform – scattered; most numerous on sides and tips • Circumvallate –largest; least numerous; back of tongue

4. Structure of a taste bud. • Supporting cells – form bulk, insulate • Receptor (Gustatory or Taste) cells – contain gustatory hairs that extend through surface • Basal cells - stem cells that divide giving rise to new gustatory cells

5. Taste sensation • Sour – stimulated by acids • Sweet – stimulated by sugars, alcohols, some amino acids • Bitter – stimulated by bases • Salty – stimulated by metal ions

6. Sensitivity of the taste buds in different locations. • Anterior tongue is more sensitive to sweet and salty substances • Posterior tongue is more sensitive to bitter substances. • Lateral tongue is more sensitive to sour substances.

8. Physiology of taste. • Chemical comes in contact with gustatory hair cells on receptor cells. • Depolarization of taste cells results in generation of action potentials in associated sensory neurons. • Relayed to the gustatory cortex. • Other sensations • Taste is 80% smell • Affected by temperature; texture; heat

9. Smell • Localization and structure of olfactory receptors • Detects chemicals in solution • Olfactory epithelium - Contains the olfactory receptors and is located in the roof of the nasal cavity.

11. Structure of olfactory receptors. • Supporting cells – • Basal cells – • Olfactory receptor cells –

13. Specificity of the olfactory receptors – • Can distinguish 10,000 chemicals • Not clearly understood • May be 1000 odorant binding proteins that act in combinations

14. Activation of olfactory receptors. • Chemical comes in contact with the olfactory hair cells on the receptor cells. • Depolarization of the receptor cells results in the generation of action potentials.

15. Homeostatic imbalances of the chemical senses • Anosmias – without smell • Uncinate fits – temporary distortions of smell due to brain damage, psychological disorders, or even seizures

16. Vision • Accessory structures of the eye • Eyebrows • Eyelids “palpebrae” • Canthi – angles of the eyelids • Epicanthic fold – found in Asians • Lacrimal Caruncle – fleshy elevation found at medial canthus

17. Meibomian glands – Modified sebaceous glands in eyelid • Infection of these called Chalazion • Ciliary glands – between hair follicles of eyelashes • Infection of these called a Sty • Conjunctiva – mucus membrane covering eye (infection called conjunctivitis or pinkeye

18. Accessory Structures of Eye • Lacrimal apparatus • Lacrimal glands – secrete tears • Lacrimal secretions – contains mucus, antibodies, & lysosozyme • Cleanses, protects, & lubricates eye

19. Extrinsic eye muscles • Medial rectus – • Superior rectus - • Lateral rectus - • Inferior rectus - • Superior oblique - • Inferior oblique –

21. Structures of the eyeball

22. Fibrous tunic (coat) – outermost layer • Sclera – whites of the eye • Cornea – clear portion in front of eye

23. Vascular tunic (coat) – middle layer (uvea) • Choroid – vascular brown membrane • Ciliary body – encircles lens forming the: • Ciliary muscles – control lens shape • Ciliary processes - contain capillaries that secrete fluid • Suspensory ligaments – • Iris – colored portion • Pupil – opening in iris

24. Sensory tunic (Retina) – innermost layer • Pigmented layer – absorbs light • Neural layer – contains photorecptor cells • Cells of the retina. • Ganglionic cells – generate action potentials • Bipolar cells – transfer energy from receptors to ganglionic cells • Photoreceptors - sensitive to light

25. Rods – dim-light, no color, and peripheral vision • Cones – bright light, color vision • Macula lutea – “yellow spot” directly behind pupil • Fovea centralis – minute pit in center of macula lutea • Contains cones only • Macular degeneration - linked to nutritional deficiencies • Optic disc (blindspot) – location of junction with optic nerve

26. Internal chambers and fluids • Posterior segment - behind lens • Vitreous humor - clear gel • Anterior segment - in front of lens • Anterior chamber - in front of iris • Posterior chamber - between iris and lens

27. Aqueous humor - clear liquid filling anterior segment • Scleral venous sinus (Canal of Schlemm) - drains aqueous humor back into veins; located at corneal / scleral junction • Glaucoma - elevated pressure of the aqueous humor

28. Lens • Biconvex; transparent; held in place by suspensory ligaments • Lens epithelium - outer covering • Lens fibers - inner bulk of lens • made of folded proteins called crystallins • Cataracts - clouding of the lens • Age related hardening and thickening; diabetes; inadequate delivery of nutrition to lens

29. Physiology of vision • Photons - packets of light • Wavelength • Electromagnetic spectrum - all wavelengths • Visible spectrum - 400-700 nanometers • nanometer = 1 billionth of a meter • Color - reflection of different wavelengths • Red, Orange, Yellow, Green, Blue, Indigo, Violet

30. Refraction and lenses • Reflection - light bounces off a surface • Refraction - light bends as it passes through one substance to another with a different density • Lens - a transparent material curved at one or both surfaces • Convex - thicker in the center; light converges • Concave - thicker at the edges; light spreads

31. Focusing of light on the retina. • Light is refracted three times • Cornea • Entering the lens • Exiting the lens

32. Focusing for distance vision. • Eye are fixed (preset) on an object 20 feet or more away. • Ciliary muscles are completely relaxed. • Lens is stretched as thin as it can get.

33. Focusing for close vision. • Accommodation of the lens. • Ciliary muscles contract. • Lens bulges. • Constriction of the pupils - • Convergence of the eyeballs -

34. Homeostatic imbalances of refraction. • Myopia - Nearsightedness • Eyeball is too long • Image is focused in front of retina • Hyperopia - Farsightedness • Eyeball is too short • Image is focused behind the retina • Astigmatism - caused by unequal curvature in different parts of the lens

36. Photoreception. • Functional anatomy of the photoreceptors • Outer segment. • Inner segment

37. The chemistry of visual pigments. • Retinal - a light absorbing pigment • made from vitamin A • combines with opsonins forming • Rhodopsin - “purple” visual pigment of Rods • Light stimulation separates retinal from the opsins • Retinal will be re-joined with the opsins to regenerate rhodopsin later

38. Different types of opsins in cones. • 3 Different types of Cones • Blue - absorbs blue wavelengths best • Green - absorbs green wavelengths best • Red - absorbs red wavelengths best • Cone wavelengths overlap • Stimulation of various cones in different amounts creates different shading and coloration

39. Color blindness - • Sex-linked, genetic trait • Lack specific types of cones, usually red or green

43. Light transduction in photoreceptors. • Generation of electrical current • Photoreceptors depolarize in dark and hyperpolarize in light • Produce graded potentials (local) • Action potentials produced by Ganglion cells

44. Light and dark adaptation - • Light adaptation - from dark to light (5-10 minutes) • Dark adaptation - from light to dark (20-30 minutes)

45. Binocular vision and stereopsis • Anterior placement of eyes results in greater depth perception or three-dimensional vision

46. Hearing and balance • Structure of the ear • Outer (External) ear. • Auricle (pinna) • External auditory canal (meatus) • Ceruminous glands - wax glands • Tympanic membrane - “eardrum” • boundary between outer and middle ear

48. Middle ear (Tympanic cavity) • Mastoid antrum - canal leading to mastoid process • Pharyngotympanic (auditory or eustachian) tube - equalizes pressure on eardrum • Ear ossicles. • Malleus (hammer) - • Incus (anvil) - • Stapes (stirrup) - • Ear muscles: Tensor tympani & Stapedius

50. Inner (Internal) ear • Bony (Osseous) labyrinth. • Cochlea - “snail” ; hearing • Semicircular canals - balance • Vestibule - central cavity • Membranous labyrinth. • Perilymph - surrounds membrane structures • Endolymph - fills membrane structures