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

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