3. Special senses

4. general senses Touch - mixture of general senses Skin temperature pressure pain Muscles and Joints proprioceptors - detect stretch, or tension (body’s position)

5. five special senses Localized clusters of receptors (taste buds and olfactory epithelium) Smell Taste Complex Sensory Organs (eyes and ears) Sight Hearing Equilibrium

6. the eye and vision 70% of all sensory receptors are in the eye

7. anatomy of the eye Meibomian (tarsal) glands – modified sebaceoous glands produce an oily secretion to lubricate the eye ciliary glands - modified sweat glands between the eyelashes Conjunctiva - membrane that lines the eyelids and covers part of the outer surface of the eyeball; secretes mucous to lubricate eyeball Conjuctivitis (pinkeye, its infectious form, is highly contagious)

8. anatomy of the eye Lacrimal gland- produces lacrimal fluid (tears) Tears - Dilute salt solution containing antibodies and lysozyme; Protects, moistens, and lubricates the eye Lacrimal canals - drains tears from eyes into the nasal cavity

9. extrinsic eye muscles

10. internal structures of eyeball Eyeball - hollow sphere composed of three tunics, or coats: Sclera - outer thick, white connective tissue; clear, central area is the cornea, which allows light to enter eye (Cornea can be transplanted without fear of rejection.) Choroid - blood-rich nutritive tunic that contains dark pigment to prevent light from scattering inside the eye; anteriorly, it forms the ciliary body (smooth muscle) and the iris (pigmented layer with pupil opening) Retina - inner, sensory tunic; contains millions of photoreceptor cells, rods and cones

11. internal structures of eyeball Lens - flexible, biconvex crystal-like structure for focusing, separates the eye into fluid-filled chambers Anterior segment contains aqueous humor - clear watery fluid, provides nutrients for lens and cornea, reabsorbed into blood through canal of Schlemm Posterior segment contains vitreous humor - gel- like substance, helps maintain intraocular pressure

12. internal anatomy of eyeball

13. Retina

14. Retina Rods - allow us to see gray tones in dim light and provide for our peripheral vision Cones - allow us to see color; three varieties - one responds to blue light, one to green, and the third to green and red wavelengths; simultaneous impulses are seen as intermediate colors Fovea centralis - point of sharpest vision, area lateral to the blind spot that contains only cones Blind spot - no photoreceptors at optic disc, where optic nerve leaves the eyeball

15. Colorblindness - lack of one or more of the cone types

16. Lens Accommodation Light must be focused to a point on the retina for optimal vision The eye is set for distance vision (over 20 ft away) The lens must change shape to focus for closer objects

17. Images formed on the Retina

18. Visual Pathway Photoreceptors of retina Optic Nerve Optic Nerve crosses at Optic chiasma Optic tracts Thalamus Visual cortex of occipital lobe

19. Eye Reflexes Internal muscles are controlled by the autonomic nervous system Bright light causes pupils to constrict through action of radial and ciliary muscles Viewing close objects causes accommodation (adjustment of lens shape) External muscles control eye movement to follow objects Viewing close objects causes convergence (eyes moving medially)

20. the ear

21. Houses two senses: Hearing Equilibrium (balance) Receptors are mechanoreceptors Different organs house receptors for each sense

22. anatomy of ear Divided into three areas: Outer (external) ear Middle ear Inner ear

23. external ear Involved in hearing only Structures: Pinna (auricle) External auditory canal -narrow chamber extending to eardrum, contains ceruminous (wax) glands

24. middle ear (tympanic cavity) Air-filled cavity within the temporal bone Only involved in the sense of hearing The opening from the auditory canal is covered by the tympanic membrane The auditory tube connecting the middle ear with the throat Allows for equalizing pressure during yawning or swallowing This tube is otherwise collapsed

25. bones of the middle ear Three ossicles (bones): Hammer (malleus) Anvil (incus) Stirrup (stapes) Vibrations from the eardrum move the malleus and transfer sound to the inner ear

26. inner ear or bony labyrinth Includes sense organs for hearing and balance Filled with perilymph A maze of bony chambers within the temporal bone: Cochlea Vestibule Semicircular canals

27. 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 attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

28. organs of hearing

29. mechanism 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

30. organs of equilibrium Receptor cells are in two structures: Vestibule Semicircular canals

31. organs of equilibrium Equilibrium has two functional parts: Static equilibrium - which way is up/down Dynamic equilibrium - movement in three planes

32. static equilibrium Maculae – receptors in the vestibule Report on the position of the head Send information via the vestibular nerve 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.

33. dynamic equilibrium Crista ampullaris – receptors in the semicircular canals Tuft of hair cells Cupula (gelatinous cap) covers the hair cells Action of angular head movements: The cupula stimulates the hair cells. An impulse is sent via the vestibular nerve to the cerebellum.

34. chemical senses - taste and smell Both senses use chemoreceptors Stimulated by chemicals in solution Taste has four types of receptors Smell can differentiate a large range of chemicals Both senses complement each other and respond to many of the same stimuli

35. olfaction - sense of smell Olfactory receptors are in the roof of the nasal cavity Neurons with long cilia Chemicals must be dissolved in mucus for detection Impulses are transmitted via the olfactory nerve Interpretation of smells is made in the cerebral cortex

36. sense of taste Taste buds house the receptor organs Location of taste buds: Most are on the Tongue Soft palate Cheeks The tongue is covered with projections called papillae: Filiform papillae – sharp with no taste buds Fungiform papillae – rounded with taste buds Circumvallate papillae – large papillae with taste buds Taste buds are found on the sides of papillae.

37. structure of taste buds Gustatory cells are the receptors Have gustatory hairs (long microvilli) Hairs are stimulated by chemicals dissolved in saliva 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

38. taste sensation Major types of taste buds: sweet receptors (sugar, saccharine, some amino acids) sour receptors (acids/hydrogen ions) bitter receptors (alkaloids) salty receptors (metal ions in solution) umami receptors - savory (glutamates) All receptors can be found on all regions of the tongue. Spicy foods excite pain receptors in the mouth.

39. developmental aspects of special senses formed early in embryological development eyes are outgrowths of brain all special senses are functional at birth Normal consequences of aging: presbyopia - age-related farsightedness presbycusis - sensorineural deafness due to atrophy of organ of Corti dulled sense of taste and smell as receptors are replaced more slowly