Understanding Sensory Systems: From Vision to Taste

1. Sensory Systems • Vision • Hearing • Taste • Smell • Equilibrium • Somatic Senses

2. Senses • Somatic sensory • General – transmit impulses from skin, skeletal muscles, and joints • Special senses - hearing, balance, vision • Visceral sensory • Transmit impulses from visceral organs • Special senses - olfaction (smell), gustation (taste)

3. Properties of Sensory Systems • Stimulus - energy source • Internal • External • Receptors • Sense organs - structures specialized to respond to stimuli • Transducers - stimulus energy converted into action potentials • Conduction • Afferent pathway • Nerve impulses to the CNS • Translation • CNS integration and information processing • Sensation and perception – your reality

4. Sensory Pathways • Stimulus as physical energy  sensory receptor acts as a transducer • Stimulus > threshold  action potential to CNS • Integration in CNS  cerebral cortex or acted on subconsciously

5. Classification by Function (Stimuli) • Mechanoreceptors – respond to touch, pressure, vibration, stretch, and itch • Thermoreceptors – sensitive to changes in temperature • Photoreceptors – respond to light energy (e.g., retina) • Chemoreceptors – respond to chemicals (e.g., smell, taste, changes in blood chemistry) • Nociceptors – sensitive to pain-causing stimuli • Osmoreceptors – detect changes in concentration of solutes, osmotic activity • Baroreceptors – detect changes in fluid pressure

6. Somatic Senses • General somatic – include touch, pain, vibration, pressure, temperature • Proprioceptive – detect stretch in tendons and muscle provide information on body position, orientation and movement of body in space

7. Somatic Receptors • Divided into two groups • Free or Unencapsulated nerve endings • Encapsulated nerve endings - consist of one or more neural end fibers enclosed in connective tissue

8. Free Nerve Endings • Abundant in epithelia and underlying connective tissue • Nociceptors - respond to pain • Thermoreceptors - respond to temperature • Two specialized types of free nerve endings • Merkel discs – lie in the epidermis, slowly adapting receptors for light touch • Hair follicle receptors – Rapidly adapting receptors that wrap around hair follicles

9. Encapsulated Nerve Endings • Meissner’s corpuscles • Spiraling nerve ending surrounded by Schwann cells • Occur in the dermal papillae of hairless areas of the skin • Rapidly adapting receptors for discriminative touch • Pacinian corpuscles • Single nerve ending surrounded by layers of flattened Schwann cells • Occur in the hypodermis • Sensitive to deep pressure – rapidly adapting receptors • Ruffini’s corpuscles • Located in the dermis and respond to pressure • Monitor continuous pressure on the skin – adapt slowly

10. Encapsulated Nerve Endings - Proprioceptors • Monitor stretch in locomotory organs • Three types of proprioceptors • Muscle spindles – monitors the changing length of a muscle, imbedded in the perimysium between muscle fascicles • Golgi tendon organs – located near the muscle-tendon junction, monitor tension within tendons • Joint kinesthetic receptors - sensory nerve endings within the joint capsules, sense pressure and position

11. Muscle Spindle & Golgi Tendon Organ

12. The Special Senses

13. 5 Special Senses • Olfaction • Gustation • Hearing • Equilibrium • Vision

14. Olfactory Organs • Located in nasal cavity on either side of nasal septum Figure 17–1a

15. Contains • Olfactory receptors • Supporting cells • Basal (stem) cells

16. Olfactory Receptors • Highly modified neurons • Involves detecting dissolved chemicals as they interact with odorant-binding proteins Figure 17–1b

17. Taste (Gustatory) Receptors • Clustered in taste buds • Associated with epithelial projections (lingual papillae) on dorsal surface of tongue • Each taste bud contains: • basal (stem) cells • gustatory cells: • Extend taste hairs through taste pore • Survive only 10 days before replacement

18. Primary Taste Sensations • Sweet • Salty • Sour • Bitter • Umami • Taste vs Flavor

19. The Ear Figure 17–20

20. External Ear • Auricle • Surrounds entrance to external acoustic canal • Protects opening of canal • Provides directional sensitivity • External acoustic canal • Canal that runs from auricle to tympanic membrane • Tympanic membrane (Eardrum) • Is a thin, semitransparent sheet • Separates external ear from middle ear

21. External Ear Figure 17–20

22. Ceruminous Glands • Integumentary glands along external acoustic canal • Secrete waxy material (cerumen): • keeps foreign objects out of tympanic membrane • slows growth of microorganisms in external acoustic canal

23. 3 Auditory Ossicles • Malleus (hammer) • Incus (anvil) • Stapes (stirrup)

24. Vibration of Tympanic Membrane • Converts arriving sound waves into mechanical movements • Auditory ossicles conduct vibrations to inner ear

25. Inner Ear Figure 17–20

26. Inner Ear • Contains fluid • Subdivided into: • vestibule • semicircular canals • cochlea

27. Parts to Inner Ear • Vestibular Complex • Combination of vestibule and semicircular canals • Vestibule • Receptors provide sensations of gravity and linear acceleration • Semicircular Canals • Contain semicircular ducts • Receptors stimulated by rotation of head • Cochlea • Contains cochlear duct • Receptors provide sense of hearing

28. Parts to Inner Ear

29. Equilibrium • Sensations provided by receptors of vestibular complex • https://www.youtube.com/watch?v=KuiNueVxdec

30. Sound • Consists of waves of pressure through air or water

31. Wavelength • Distance between 2 adjacent wave troughs • Frequency • Number of waves that pass fixed reference point at given time • Physicists use term cycles instead of waves • Hertz (Hz) • Number of cycles per second (cps)

32. Pitch • Our sensory response to frequency • Increased frequency results in a higher pitch • Decreased frequency results in a lower pitch

33. Amplitude • Intensity of sound wave • Sound energy is reported in decibels

34. The Power of Sounds Table 17–1

35. How do we hear? • Sound waves enter external acoustic canal • Soundwaves vibrate the tympanic membrane • Vibrations are transferred to and through the auditory ossicles • Vibrations are transferred to fluid in cochlea • Nerve endings pick up vibrations and send signal to brain

36. How do we hear?

37. Accessory Structures of the Eye • Eyelids • Superficial epithelium of eye • Structures associated with production, secretion, and removal of tears

38. Eyelids (Palpebrae) • Continuation of skin • Blinking keeps surface of eye lubricated, free of dust, and debris

39. Eyelashes • Robust hairs that prevent foreign matter from reaching surface of eye

40. Tarsal Glands • Associated with eyelashes • Secrete lipid–rich product that helps keep eyelids from sticking together • Contribute to gritty deposits that appear after good night’s sleep

41. Conjunctiva • Epithelium covering inner surfaces of eyelids and outer surface of eye • Conjunctivitis • Results from damage to conjunctival surface Figure 17–3b

42. Cornea • Transparent part of outer fibrous layer of eye

43. Lacrimal Gland(Tear Gland) • Secretions contain lysozyme, an antibacterial enzyme • Lubricates, cleanses, disinfects eye

44. Orbital Fat • Cushions and insulates eye Figure 17–4c

45. Eyeball • Is hollow • Is divided into 2 cavities: • large posterior cavity • smaller anterior cavity

46. Outer Surface of Eye • Sclera (white of eye) • Cornea

47. Middle Layer of Eye • Includes: • iris • ciliary body • Iris • Contains muscle fibers • Changes diameter of pupil • Ciliary body • Assist in changing shape of lens for focusing images

48. Middle Layer of Eye

49. Lens • Lies posterior to cornea • Forms anterior boundary of posterior cavity

50. Inner Layer of Eye (Retina) • Outer pigmented part • Inner neural part: • contains visual receptors and associated neurons