The Special Senses

1. The Special Senses

2. Objectives: • List and describe the major forms of special senses. • Identify the location, the structure, and function of the special sense organs. a. Tactile b. Gustation c. Olfactory d. Visual e. Auditory

3. Tactility: Touch • Specialized nerve receptors are located in the dermal layers of the skin which are sensitive to pressure associated with touch, heat, cold, and pain. These are specially modified sensory neurons called receptors. There are also receptors in muscle tissue which detect stretching, force of contraction and the stretching of tendons.

4. Skin Receptors • Skin: I. Free nerve endings: a. Nocireceptors: Temperature, mechanical (pain itching, tickle, stretching) Dermis b. Merkel discs: Light pressure, mechanical (discriminative touch) Dermis c. Root hair plexus: Hair movement, mechanical dermis II.Encapsulated Nerve Endings: a. Meissner’s corpuscle: light pressure mechanical, Located in hairless areas, palms or hands and soles of feet. (discriminative touch, vibrations.) Dermis b. Ruffini’s corpuscle: mechanical, thermal (rough and persistent touch) Dermis c. Krauses corpuscle: mechanical, thermal (touch, low frequency vibrations) Dermis of mucus membranes d. Pacinian corpuscle: Deep pressure, mechanical (deep pressure, stretch, and high frequency vibrations) Dermis of skin and joint capsules

5. Skin Receptors

6. Muscle Receptors • Muscle I. Encapsulated nerve endings a. Muscle spindles: stretch, mechanical, sense of muscle length, all skeletal muscle b. Golgi tendon receptors: stretch mechanical, muscle tension

7. Gustation: Taste • Taste buds: • located on the tongue, some are located within other areas of the mouth • Papillae: small elevated projections on the tongue • Fungiform (sweet), circumvallate (bitter), and foliate (sour) contain taste buds (all taste salty) • Filiform are sensitive to touch • Gustatory cells - specialized receptors located on each taste bud (50-125 per taste bud); have special hair like projections (sensitive to various chemicals - acts as stimuli for various taste sensations) • gustatory nerves - connected by the cranial nerves to the medulla oblongata  relays the message to the thalamus  to the gustatory center of the brain where the stimulus is interpreted. • Gustation and olfaction are closely associated to produce the sensation of taste.

8. Gustation: Taste

9. Olfactory: Smell • Sensory cells - located in the epithelial lining of the mucous membrane of the nose • Olfactory neural chemoreceptors - have specialized cilia which detect the presence of specific chemicals within the air we breath • The neurons connected to the olfactory bulb when stimulated sends a message to the olfactory center of the brain where the smell is interpreted

10. Olfactory Smell

11. Auditory (Hearing) and Balance • The ear is a duel organ, not only is responsible for the sense of hearing but also it functions as the organ of balance. • The sensation of balance and hearing are both associated with specialized receptors with hair-like mechanoreceptors (hair cells). • The ear is divided into three major regions: a. External: Pinna or auricle and auditory canal b. Middle : Tympanic membrane (eardrum) and auditory ossicles ( malleus (hammer), incus (anvil) and stapes (stirrup) c. Inner: Semicircular canals and vestibular nerve (balance) and the cochlea and round or oval window and the cochlear nerve (sound)

12. Auditory (Hearing) and Balance

13. Hearing • Outer ear: • Pinna – ear flap • Collects and directs sound waves into the ear • Auditory canal – channels waves to the ear drum; houses ceruminous glands • Ceruminous glands - secrete ear wax (cerumin) to keep ear drum moist • Tympanic membrane – ear drum • Catches vibrations and sends them to the bones of the inner ear; separates the outer and middle ear

14. Hearing • Middle ear: • Eustachian tube – connects the ear to the throat and equalizes pressure • Ossicles: • Hammer (malleus) – outermost bones, receives vibrations from tympanic membrane • Anvil (incus) – middle bone • Stirrup (stapes) – innermost bone, transfers vibrations to the cochlea

15. Hearing • Inner Ear: • Vestibule – space between the cochlea and semicircular canals • Cochlea – snail shaped structure; fluid filled with endolymph and perilymph; contains the organ of corti • Organ of Corti – tiny hair-like cells that pick up vibrations and transfer them to the auditory nerve • Semicircular canals – contain liquid (perilymph) and tiny hair-like cells that blend with motion to help maintain equilibrium • Auditory nerve – carries information from the ear to the temporal lobe of the brain

16. Hearing • Inner ear continued: • Perilymph – thin liquid in spaces of the inner ear • Endolymph – thick liquid found in the cochlear ducts of the inner ear

17. Auditory (Hearing) • Pinna is designed to capture sound vibrations and channel them into the auditory canal. • The tympanic membrane transfers the sound vibrations to the auditory ossicles of the middle ear. • The auditory ossicles then transfer the vibrations to the round window of the cochlea.

18. Auditory (Hearing) • Within the cochlea is the organ of Corti where the hair cells are located. Each respond to a different frequency of vibration. • The cochlea have canals which are filled with fluid, which surrounds the Organ of Corti. • When the fluid is stimulated by vibrations from the round window, the fluid transfers the vibrations to the hair cells, which then transfers the message to the auditory center of brain for interpretation through the acoustic nerve

19. Hearing pathway • Pinna  auditory canal  tympanic membrane  malleus  incus  stapes  cochlea  Organ of Corti  auditory nerve  temporal lobe of brain

20. Hearing disorders • Presbyscusis – deafness with aging, caused by bones fusing; fusion makes them unable to transfer vibrations; hearing aids can help • Vertigo – dizziness, variety of causes • Meniere’s disease – condition of they labyrinth (semicircular canals) which causes marked vertigo and fullness of the ear; may require bed rest

21. Hearing disorders • Otitis media – middle ear infection; build up of fluid caused by bacteria • Otosclerosis – bones of the ear become immovable; causes deafness because the stapes fuses with the bone of the ear and does not allow sound vibrations to transfer to the cochlea • Tinnitus – ringing in the ear; caused by wax build up, infection, exposure to loud sounds

22. Balance

23. Balance

24. Quiz Key Choices Malleus Tympanic membrane Incus Pinna Cochlea Auditory canal Eustachian tube Semicircular canals 1. 6. 5. 3. 4. 2.

25. Vision • The eye is the organ of vision. • It converts light energy into electrical nerve impulses which are then interpreted by the brain as sight. • The lens of the eye focus light on the retina. • The retina contain specialized nerve receptors sensitive to light intensity (rods) and wavelengths or colors of light (cones). • The optic nerve then carries the message to the brain where it is interpreted as sight in the visual center of the occipital lobes.

26. Vision • Conjunctiva – the thin, transparent tissue that covers the outer surface of the eye • Secretes oils and mucus that moisten and lubricate the eye • Cornea – clear, allows light to enter the eye. • Most anterior part of the eye. • Eye lashes – protect the eye from debris • Eye lid – works to keep the eye moist (blink)

27. Vision • Sclera – the white of the eye • Holds the shape and protects the inner eye • Lens – directs images to the retina; helps focus on images by changing shape • Lacrimal gland – produces tears • Tears cleanse and moisten they eye, kills bacteria • Pupil – a space in the iris where light enters • Iris – the colored part of the eye; muscular • Controls the amount of light entering the eye by changing the size of the pupil

28. Vision • Choroid coat – middle of the 3 eye layers; has dark pigment to keep light from scattering • Aqueous humor – watery substance anterior to the lens; helps maintain shape of eye ball and refracts light • Vitreous humor – jelly-like substance found posterior to the lens inside the eyeball; helps maintain eyeball shape and refracts light

29. Vision • Ciliary body – muscle that controls the shape of the lens • Suspensory ligaments – hold the lens in place • Retina – interior most layer of the eye • Rich in nerve cells • Rods – cells for dim light • Cones – receptor cells for sensitivity to bright light (color) • Macula – center region of the retina; area for sharp central vision

30. Vision • Optic Nerve – carries impulse from the retina to the occipital lobe of the brain • Optic disk – blind spot; no receptors therefore no vision • Fovea centralis – site of cones • Extrafovial region – area of rods • Also where peripheral vision occurs

31. Eye Structure

32. Retina Structure

33. Visual pathway • Cornea  aqueous humor  iris & pupil  lens  vitreous humor  retina  optic nerve  occipital lobe of brain

34. Light Refraction

35. Common Refraction Disorders

36. Eye Disorders • Myopia – nearsighted • The eye is long so the image forms in front of the retina • Hyperopia – farsighted • The eye is short so the image forms behind the retina

37. Eye Disorders • Cataracts – clouding of the lens, usually due to aging

38. Eye Disorders • Glaucoma – excess aqueous humor puts pressure on the retina, causing damage (usually caused by aging) • Strabismus – cross-eyes; eye muscles are not properly coordinated

39. Ishihara Color Blindness Test Normal Color Vision 25 29 45 56 6 8

40. Ishihara Color Blindness Test Red-Green Color Blind 25 Spots Spots 56 Spots spots

41. normal color vision: 5 revealed in the dot pattern. Red/Green color blindness: 2 revealed in the dots. Ishihara Color Blindness Test