1. Chapter 17, part 1
The Special Senses

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. SECTION Olfaction

5. 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

6. Figure 17.1 The Olfactory Organs
Figure 17.1a, b

7. 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

8. SECTION Gustation

9. Taste receptors Clustered in taste buds
Associated with lingual papillae

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

11. Figure 17.2 Gustatory Reception

12. 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

13. 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

14. SECTION Vision

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

16. Figure 17.3 Eternal Features and Accessory Structures of the Eye
Figure 17.3a, b

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

18. 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

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

20. Figure 17.4 The Sectional Anatomy of the Eye
Figure 17.4a, b

21. 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

22. Figure 17.4 The Sectional Anatomy of the Eye
Figure 17.4c

23. Figure 17.5 The Pupillary Muscles

24. 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

25. Figure 17.6 The Organization of the Retina
Figure 17.6a

26. Figure 17.6 The Organization of the Retina
Figure 17.6b, c