Somatic Senses & Special Senses

1. Somatic Senses & Special Senses Chapter 12

2. Special Senses (Special Location) • Smell (olfaction) • taste (gustation) • vision • balance • hearing

3. General Senses (Somatic & Visceral) • Temperature • Touch • Pressure • Vibration • Proprioception • Pain • Internal organ conditions

4. Definition of Sensation • Conscious or subconscious awareness of change in external or internal environment • Requires: • Stimulus • Sensory receptor • Neural pathway • Brain region for integration

5. Characteristics • Perception- conscious awareness • Cerebral cortex function • Adaptation- decreased receptor response with prolonged stimulation • decreased perception Adaptation speed varies with receptor

6. Structural Types • Free nerve endings- • pain, thermal, tickle, itch & some touch receptors • Encapsulated nerve endings • Touch pressure & vibration • Specialized cells: • e.g. hair cells in inner ear

7. Receptor Mechanisms • Mechanoreceptors- • cell deformation, stretching or bending • Thermoreceptors- temperature • Nociceptors– pain • Photoreceptors- light • Chemoreceptors- chemicals • Taste, smell, body fluid content

8. Somatic Senses • Receptors- distributed unevenly • In skin, mucous membranes, muscles, tendons,& joints • Dense receptors concentration in fingertips, lips & tip of tongue

9. Tactile sensations • Touch, pressure, vibration, itch & tickle • Itch & tickle – free nerve endings • encapsulated mechanoreceptors

10. Figure 12.1

11. Itch & tickle • Itch- chemical stimulation of free nerve endings • Bradykinin from inflammation response • Tickle- from free nerve endings & lamellated corpuscles • Requires someone else- blocked by signals from cerebellum

12. Thermal Sensations • Two kinds of thermoreceptors- • Between 10o & 40o C - cold • Located in epidermis • Between 32o & 48o C – warm • located in dermis • Outside these ranges – nociceptors • Both adapt rapidly but continue slow signals during prolonged stimulus

13. Pain Sensations • Nociceptors- free nerve endings • Found in every tissue but brain • Very little adaptation • Fast pain= acute, sharp pain (0.1 sec) • not felt in deep tissues and well localized • Slow pain- slow starting & increases • Chronic, burning, aching or throbbing sensation

14. Visceral pain location displaced to surface = referred pain

15. Proprioception • Head and limb position & motion • Located in muscles (muscle spindles), tendons (tendon organs), in & around synovial joints (joint kinesthetic receptors) • Kinesthesia= perception of movements • Inner ear (hair cells)- head position • Tracts to primary sensory area of cerebral cortex & cerebellum • Slow & slight adaptation

16. Figure 10.13

17. Smell- Olfactory Pathway

18. Smell- Olfaction

19. Stimulation of Receptors • Genetic evidence- 100’s of primary odors • Binding of chemical stimulates nerve • Recognition of 10,000 odors from combination of primary receptor input • Rapid adaptation by ~50% in 1 sec.

20. Taste- Gustatory Sensation • 5 primary tastes: salt, sweet, sour, bitter & umami • Perception of what we call taste includes olfactory input • Receptors in taste buds (~10,000)

21. Taste- Gustatory Structures

22. Papillae Details

23. Figure 12.4c

24. Stimulation • Tastant- dissolved in saliva • Receptors respond to more than one tastant • Release neural transmitter to primary gustatory neuron • Tastes arise from mix of input form various areas

25. Gustatory Pathway • Facial & glossopharyngeal-tongue • vagus- pharynx & epiglottis • to medulla oblongata •  thalamus •  primary gustatory area- • consciousness • Also medulla  limbic system

26. Vision- Eyes • Accessory structures- • eye brows, eyelashes- protection • eye lids- protection & lubrication (blinking) • extrinsic muscles- moving eyeball • Superior Rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, inferior oblique

27. Lacrimal Apparatus (Tear Production)

28. Layers of the Eyeball

29. Figure 12.7

30. Back of the Eye Layers

31. Refraction of Light • Light rays bend on passing from medium of one density to another of different density = refraction • 75% occurs at cornea • Lens- focuses light on the retina • Image is inverted but brain adjusts & interprets distance and size

32. Figure 12.9a

33. Figure 12.9b

34. Figure 12.9c

35. Figure 12.10

36. Other visual controls • Constriction of pupil- • autonomic reflex to center light on lens • Convergence- eyes rotate toward midline • as object nears it is necessary to maintain focus on single object for binocular vision • Photoreceptors: light  neural signal • light is absorbed by a photopigment (rhodpsin) which splits into opsin & retinal

37. Visual Pathway

38. Detecting Diseases of the Retina Webster, John G., Bioinstrumentation, Wiley, Ch 7, 2004.

39. Mirror Examiner’s eyes Lamp Inverted image of eye Condensing lens Patient’seye Detecting Diseases of the Retina (2) Webster, John G., Bioinstrumentation, Wiley, Ch 7, 2004.

40. Major Ear Structures

41. Details of Inner Ear Structure

42. Spiral Organ Detail

43. Physiology of Hearing

44. Auditory Pathway • Cochlear neurons end on same side in medulla • Through midbrain to thalamus • Auditory Cortex on Temporal lobe • Receives input from both ears

45. Hearing Aids vs. Cochlear Implants Courtesy of Zounds Corporation In the ear (ITE) and behind the ear (BTE) hearing aids amplify sounds (Above). Cochlear implants place electrodes directly into the cochlea replacing the operation of the hair-to-nerve connections to the brain.

46. Physiology of Equilibrium • Equilibrium in part monitored in inner ear- vestibular system • Static equilibrium- position relative to gravity • Dynamic equilibrium- position in response to head movement

47. Static Equillibrium

48. Dynamic Equilibrium

49. Figure 12.15b

50. Figure 12.16b