1. Lecture 13: Chapter 17 The Special Senses Page: 549 - 589
Lecturer: Dr. Barjis
Room: P313
Phone: (718)

2. Learning Objectives
Describe the sensory organs of smell, and trace the olfactory pathways to their destination in the brain.
Identify the accessory and internal structures of the eye, and explain their function.
Explain how light stimulates the production of nerve impulses, and trace the visual pathways to their destination in the brain.
Describe the structures of the external and middle ear and explain how they function.

3. Learning Objectives
Describe the parts of the inner ear and their roles in equilibrium and hearing.
Trace the pathways for the sensations of equilibrium and hearing to their destinations in the brain.

4. Olfaction Olfactory organs
Contain olfactory epithelium with olfactory receptors, supporting cells, basal cells
Olfactory receptors are modified neurons
Surfaces are coated with secretions from olfactory glands
Olfactory reception involved detecting dissolved chemicals as they interact with odorant binding proteins

5. The Olfactory Organs

6. Olfaction Olfactory pathways
No synapse in the thalamus for arriving information
Olfactory discrimination
Can distinguish thousands of chemical stimuli
CNS interprets smells by pattern of receptor activity
Olfactory receptor population shows considerable turnover
Number of receptors declines with age

7. Gustation Taste receptors Clustered in taste buds
Associated with lingual papillae

8. Taste buds Contain basal cells which appear to be stem cells
Gustatory cells extend taste hairs through a narrow taste pore

9. Gustatory Reception

10. Gustatory pathways Taste buds are monitored by cranial nerves
Synapse within the solitary nucleus of the medulla oblongata
Then on to the thalamus and the primary sensory cortex

11. Gustatory discrimination
Primary taste sensations
Sweet, sour, salty, bitter
Receptors also exist for umami and water
Taste sensitivity shows significant individual differences, some of which are inherited
The number of taste buds declines with age

12. Accessory structures of the eye
Vision
Accessory structures of the eye
Eyelids (palpebrae) separated by the palpebral fissue
Eyelashes
Tarsal glands
Lacrimal apparatus

13. Eternal Features and Accessory Structures of the Eye

14. external structures of the eye
Conjunctiva covers most of eye
Cornea is transparent anterior portion

15. Lacrimal apparatus Secretions from the lacrimal gland contain lysozyme
Tears form in the lacrimal glands, wash across the eye and collect in the lacrimal lake
Pass through the lacrimal punctae, lacrimal canaliculi, lacrimal sac and nasolacrimal duct

16. The eye Three layers Outer fibrous tunic Sclera, cornea, limbus
Middle vascular tunic
Iris, ciliary body, choroid
Inner nervous tunic
Retina

17. The Sectional Anatomy of the Eye

18. internal structures of the eye
Ciliary body
Ciliary muscles and ciliary processes, which attach to suspensory ligaments of lens
Retina
Outer pigmented portion
Inner neural part
Rods and cones

19. The Sectional Anatomy of the Eye

20. The Pupillary Muscles

21. retina Retina contains rods and cones
Cones densely packed at fovea (center of the macula lutea)
Retinal pathway
Photoreceptors to bipolar cells to ganglion cells, to the brain via the optic nerve
Axons of ganglion cells converge at blind spot (optic disc)
Horizontal cells and amacrine cells modify the signal passed along the retinal neurons

22. The Organization of the Retina

23. The Organization of the Retina

24. Eye anatomy
Ciliary body and lens divide the anterior cavity of the eye into posterior (vitreous) cavity and anterior cavity
Anterior cavity further divided
anterior chamber in front of eye
posterior chamber between the iris and the lens

25. The Circulation of Aqueous Humor

26. Fluids in the eye Aqueous humor circulates within the eye
diffuses through the walls of anterior chamber
passes through canal of Schlemm
re-enters circulation
Vitreous humor fills the posterior cavity.
Not recycled – permanent fluid

27. Lens
Posterior to the cornea and forms anterior boundary of posterior cavity
Posterior cavity contains vitreous humor
Lens helps focus
Light is refracted as it passes through lens
Accommodation is the process by which the lens adjusts to focus images
Normal visual acuity is 20/20

28. Image Formation

29. Accommodation
Figure 17.10

30. Visual Abnormalities

31. Visual physiology Rods – respond to almost any photon
Cones – specific ranges of specificity

32. Rods and Cones

33. Photoreceptor structure
Outer segment with membranous discs
Narrow stalk connecting outer segment to inner segment
Light absorption occurs in the visual pigments
Derivatives of rhodopsin

34. Photoreception
Animation: Photoreception (see tutorial)

35. Photoreception

36. Bleaching and Regeneration of Visual Pigments

37. Color sensitivity
Integration of information from red, blue and green cones
Colorblindness is the inability to detect certain colors

38. retinal adaptation
Dark adapted – most visual pigments are fully receptive to stimulation
Light adapted – pupil constricts and pigments bleached.

39. the visual pathway Large M-cells monitor rods
Smaller more numerous P cells monitor cones

40. Convergence and Ganglion Cell Function

41. Seeing in stereo
Vision from the field of view transfers from one side to the other while in transit
Depth perception is obtained by comparing relative positions of objects from the two eyes

42. The Visual Pathways

43. Visual circadian rhythm
Input to suprachiasmic nucleus affects the function of the brainstem
Circadian rhythm ties to day-night cycle, and affects metabolic rates

44. Equilibrium and Hearing
Both equilibrium and hearing are provided by
receptors of the inner ear
Anatomy of the ear – External Ear
Auricle or pinnae surrounds the ear
External acoustic meatus ends on tympanic membrane

45. The Anatomy of the Ear

46. Middle ear Communicates with pharynx via pharyngotympanic membrane
Middle ear encloses and protects the auditory ossicles

47. The Middle Ear

48. Inner ear Membranous labyrinth contains endolymph
Bony labyrinth surrounds and protects membranous labyrinth
Vestibule
Semicircular canals
Cochlea

49. The Inner Ear
Figure 17.22

50. Components of the inner ear
Vestibule contains the utricle and saccule
Semicircular canals contain the semicircular ducts
Cochlea contains the cochlear duct

51. Windows
Round window separates the perilymph from the air spaces of the middle ear
Oval window connected to the base of the stapes
Basic receptors of inner ear are hair cells
Provide information about the direction and strength of stimuli

52. Equilibrium
Anterior, posterior and lateral semicircular ducts are continuous with the utricle
Each duct contains an ampulla with a gelatinous cupula and associated sensory receptor
Saccule and utricle connected by a passageway continuous with the endolymphatic duct
Terminates in the endolymphatic sac
Saccule and utricle have hair cells clustered in maculae
Cilia contact the otolith (statoconia)

53. The Vestibular Complex

54. The Vestibular Complex

55. The Vestibular Complex

56. Vestibular neural pathway
Vestibular receptors activate sensory neurons of the vestibular ganglia
Axons form the vestibular branch of cranial nerve VII
Synapses within the vestibular nuclei

57. Pathways for Equilibrium Sensation

58. Hearing
Cochlear duct lies between the vestibular duct and the tympanic duct
Hair cells of the cochlear duct lie within the Organ of Corti
Intensity is the energy content of a sound
Measured in decibels

59. The Cochlea

60. The Organ Of Corti

61. Pathway of sound
Sound waves travel toward tympanic membrane, which vibrates
Auditory ossicles conduct the vibration into the inner ear
Tensor tympani and stapedius muscles contract to reduce the amount of movement when loud sounds arrive
Movement at the oval window applies pressure to the perilymph of the cochlear duct
Pressure waves distort basilar membrane
Hair cells of the Organ of Corti are pushed against the tectoral membrane

62. Sound and Hearing

63. Sound and Hearing

64. Neural pathway
Sensory neurons of hearing are located in the spiral ganglion of the cochlea
Afferent fibers form the cochlear branch of cranial nerve VIII
Synapse at the cochlear nucleus

65. You should now be familiar with:
The sensory organs of smell, and the olfactory pathways in the brain.
The accessory and internal structures of the eye, and their functions.
How light stimulates the production of nerve impulses, and the visual pathways.
The structures of the external and middle ear and how they function.
The parts of the inner ear and their roles in equilibrium and hearing.
The pathways for the sensations of equilibrium and hearing.