Somatic Senses & Special Senses

1. Somatic Senses & Special Senses Chapter 12

2. Special Sensesspecial location • Smell (olfaction) • taste (gustation) • vision • balance • hearing

3. General SensesSomatic & 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. Touch • Rapidly adapting receptors: • Meisner corpuscles • Hair root plexuses • Slowly adapting receptors: • Type I mechanoreceptors= Merkel discs- • surface receptors- stratum basale • Type II mechanoreceptors= Ruffini corpuscles- deep in dermis & tendons

11. Pressure & Vibration • Sensation over large area • Lamellated or Pacinian corpuscles • Rapid adapting & widely distributed • Vibration = rapidly repetitive stimuli • Corpuscles of touch- low frequency • Lamellated corpuscles- higher frequency

12. Figure 12.1

13. 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

14. 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

15. 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 • Visceral pain location displaced to surface = referred pain

16. Figure 12.2

17. 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 ceils)- head position • Tracts to primary sensory area of cerebral cortex & cerebellum • Slow & slight adaptation

18. Figure 10.13

19. Smell- Olfaction • In upper surface of superior concha, below cribiform plate • Olfactory receptors- • first order neurons of olfactory pathway • Connect to olfactory bulb • Have olfactory hairs containing chemoreceptors • Supporting cells- • epithelial cells – support & electrical insulation • Basal cells- stem cells for receptors

20. Figure 12.3a

21. 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.

22. Olfactory Pathway • Olfactory receptor’s axons = Olfactory nerves • through cribiform plate  olfactory bulbs • Olfactory tract • To primary olfactory area of temporal lobe • And limbic system - emotional response to smells, e.g. nausea or arousal

23. Figure 12.3 b

24. 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) • Located on tongue & pharynx & epiglottis • In structures called papillae • Vallate (back), fungiform (all over) • filiform- touch receptors only

25. Figure 12.4a

26. Figure 12.4b

27. Structure of Taste Bud • Epithelial cells: • Supporting cells surrounding • Gustatory receptor cells • Gustatory hair projects from receptor through taste pore • Basal cells= stem cells • Produce supporting cells that develop into receptor cells (10 day life span)

28. Figure 12.4c

29. 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

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

31. 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 • Lacrimal apparatus- • Gland lacrimal duct surface of upper eyelid  lacrimal canal & nasolacrimal duct  nasal cavity

32. Figure 12.5

33. Layers of Eyeball • Fibrous tunic – Anterior clear cornea • Sclera- white of eye • Vascular tunic- contains: • Choroid- Lines most of internal surface • carries blood vessels • Ciliary body- focuses the lens and secretes aqueous humor • Iris- opens & closes pupil- • contains pigment of eye color. • Pupil = hole for light passage • Adjusted by iris to control amount of light through the lens

34. Figure 12.6

35. Figure 12.7

36. Layers of Eyeball (Cont.) • Retina- two layers • neural layer- outgrowth of brain • Photoreceptor layer • Bipolar cell layer • Ganglion cell layer • pigmented layer- helps absorb stray light • between choroid & neural layer

37. Photoreceptors • Rods very sensitive, black & white • Cones- color sensitive, • 3 types-blue, green & red • Color vision results from combined input • Cones mostly in central fovea in center of macula lutea • Area of highest visual resolution • Information  bipolar layer ganglion cells axons = optic nerve

38. Figure 12.8

39. Interior of Eyeball • Two cavities- Anterior cavity & Vitreous Chamber divided by lens • Anterior filled with aqueous humor • Drains into canal of schlemm.- replaced ~90 min. • Maintains eye shape & nourishes lens & cornea • Responsible for intraocular pressure • Vitreous chamber- filled with vitreous body • Gel-like - holds retina against choroid

40. 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

41. Figure 12.9a

42. Figure 12.9b

43. Figure 12.9c

44. Accommodation • Lens adjusts for distance to keep image focused on retina • With distant objects ciliary muscle is relaxed • Contracts as the object becomes closer • Myopia= can’t accommodate distant objects- Eyeball is too long • Hyperopia = can’t accommodate far objects- Eyeball is too short • Astigmatism= irregular curvature of cornea or lens

45. Figure 12.10

46. 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

47. Visual Pathway • Optic nerve through optic chiasm • About 1/2 cross over into optic tract •  hypothalamus occipital lobes • Right brain sees left side of object • Left brain sees right side of object

48. Figure 12.11

49. Structures • Outer ear- Auricle, external auditory canal & tympanic membrane (ear drum) • Canal contains hairs & ceruminous glands • Middle ear- auditory tube (eustachian tube) & ossicles • Ossicles = Malleus, incus, & stapes-attached to oval window • Inner ear- Bony labyrinth & membranous labyrinth filled with endolymph • Cochlea- sense organ of hearing , • vestibule & semicircular canals- organs of balance

50. Figure 12.12