Chapter 17, part 1

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 17-1Olfaction

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 17-2Gustation

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 Figure 17.2

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 17-3Vision

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 Figure 17.5