Chapter 6B The Peripheral Nervous System: Special Senses

1. Chapter 6B The Peripheral Nervous System: Special Senses

2. Outline • Pathways, perceptions, sensations • Receptor Physiology • Receptors have differential sensitivities to various stimuli. • A stimulus alters the receptor’s permeability, leading to a graded receptor potential. • Receptor potentials may initiate action potentials in the afferent neuron. • Receptors may adapt slowly or rapidly to sustained stimulation. • Each somatosensory pathway is “labeled” according to modality and location. • Acuity is influenced by receptive field size and lateral inhibition. • PAIN • Stimulation of nociceptors elicits the perception of pain plus motivational and emotional responses. • The brain has a built-in analgesic system.

3. Cortex • Higher processing • Basal nuclei • Control of movement, inhibitory, negative • Thalamus • Relay and processing of sensory information • Awareness, a positive screening center for information • Hypothalamus • Hormone secretion, regulation of the internal environment • Cerebellum • Important in balance and in planning and executing voluntary movement • Brain Stem • Relay station (posture and equilibrium), cranial nerves, control centers, reticular integration, sleep control

4. What did you learn from the vision lab? • Color blindness • Rod and cone function • What an astigmatism is • After imaging? positive and negative after images

5. Vision outline • Anatomy • Muscles and light control • Refraction and refractive structures • Refractive problems • Retina, photoreceptors, transduction • Visual cortical processing

6. Countercurrent exchange • Found in many animal systems • thermoregulation, and in the kidney • The transfer of a substance flowing in one direction to another moving in the opposite direction • Efficient - gill can remove 80 % of O2

7. AnatomyEye protection • Eyelids • Act like shutters to protect eye from environmental hazards • Eyelashes • Trap fine, airborne debris such as dust before it can fall into eye • Tears • Continuously produced by lacrimal glands • Lubricate, cleanse, bactericidal • Eyesocket

8. middle layer underneath • sclera which • contains blood vessels • that nourish retina Eye • tough outer layer of connective tissue; • forms visible white part of the eye Circular and radial muscle controlling the amt. of light entering eye opening • anterior, transparent outer layer through • which light rays pass into interior of eye • Maintains eye shape Aqueous humor is formed by capillary network in ciliary body, then drains into the canal of Schlemm, and eventually enters the blood. • Nutrients for cornea and lense

9. Eye • Interior consists of two fluid-filled cavities separated by the lens • Posterior cavity • Larger cavity between lens and retina • Contains vitreous humor • Important in maintaining the spherical shape of eyeball • Anterior cavity • Anterior cavity between cornea and lens • Contains aqueous humor • Carries nutrients for cornea and lens • Produced by capillary network within ciliary body • Fovea • Pinhead-sized depression in exact center of retina • Point of most distinct vision • Has only cones • Macula lutea • Area immediately surrounding fovea • Fairly high acuity • Macular degeneration • Leading cause of blindness in western hemisphere

10. Vision outline • Anatomy • Light and muscle control • Refraction and refractive structures • Refractive problems • Retina, photoreceptors, transduction • Visual cortical processing

11. Eye • Convex structures of eye produce convergence of diverging light rays that reach eye

12. Eye Focusing on Distant and Near Light Sources What happens to light rays when they leave the light source?

13. Eye • Two structures most important in eye’s refractive ability are • Cornea • Contributes most extensively to eye’s total refractive ability • Refractive ability remains constant because curvature never changes • Lens • Refractive ability can be adjusted by changing curvature as needed for near or far vision • Accommodation • Change in strength and shape of lens • Accomplished by action of ciliary muscle and suspensory ligaments • Age-related reduction in accommodation ability - presbyopia

14. Mechanics of Accommodation Near vision Far vision * Light moves towards thick part of lens

15. Fig. 6-11, p. 193

16. Vision outline • Anatomy • Muscles and light control • Refraction and refractive structures • Refractive problems • Retina, photoreceptors, transduction • Visual cortical processing

17. Emmetropia, Myopia, and Hyperopia

18. Vision outline • Anatomy • Muscles and light control • Refraction and refractive structures • Refractive problems • Retina, photoreceptors, transduction • Visual cortical processing

19. Retinal Layers • Retina – receptor containing portion is actually an extension of the CNS • Neural portion of retina consists of three layers of excitable cells • Outermost layer containing rods and cones • Middle layer of bipolar cells • Inner layer of ganglion cells • Axons of ganglion cells join to form optic nerve • Point on retina at which optic nerve leaves is the optic disc • Region often called the blind spot because no image can be detected here because of lack of rods and cones

20. Rod and cone cells • Consist of three parts • Outer segment • Detects light stimulus • Inner segment • Contains metabolic machinery of cell • Synaptic terminal • Transmits signal generated in photoreceptor on light stimulation to next cells in visual pathway Photoreceptors

21. Photopigments • Undergo chemical alterations when activated by light • Consists of two components • Opsin • Protein that is integral part of disc membrane • Retinene • Derivative of vitamin A • Light-absorbing part of photopigment • Four different photopigments • Rod pigment • Provide vision only in shades of gray • Rhodopsin • Absorbs all visible wavelengths • Cone pigments • Respond selectively to various wavelengths of light • Make color vision possible • Red cones • Green cones • Blue cones

22. Fig. 6-25, p. 202

23. Properties of Rod Vision and Cone Vision

24. The sensitivity of the eyes varies through dark and light adaptation. • Dark adaptation • Can gradually distinguish objects as you enter a dark area. • Due to the regeneration of rod photopigments that had been broken down by previous light exposure. • Light adaptation • Can gradually distinguish objects as you enter an area with more light. • Due to the rapid breakdown of cone photopigments.

25. Vision outline • Anatomy • Muscles and light control • Refraction and refractive structures • Refractive problems • Retina, photoreceptors, transduction • Visual fields • Visual cortical processing

26. Visual Processing • Blending color • 3 cone types – blue, green, red • Stimulated in a ratio to produce blends % max • Distinguishing contours • On center and off center ganglion cells • Images on the retina are upside down and backwards. • Depth perception

27. Hearing outline • Anatomy • Outer, middle, inner • Hearing • Transmission of sound waves • Hair cells and transduction • Cochlea and canals/ducts • Pitch and loudness • Auditory cortical processing

28. Ear • Consists of three parts • External ear • Consists of pinna, external auditory meatus, and tympanum • Transmits airborne sound waves to fluid-filled inner ear • Amplifies sound energy • Middle ear • Transmits airborne sound waves to fluid-filled inner ear • Amplifies sound energy • Inner ear • Houses two different sensory systems • Cochlea • Contains receptors for conversion of sound waves into nerve impulses which makes hearing possible • Vestibular apparatus • Necessary for sense of equilibrium

29. Ear

30. Hearing outline • Anatomy • Outer, middle, inner • Hearing • Transmission of sound waves • Pitch and loudness • Hair cells and transduction • Cochlea and canals/ducts • Auditory cortical processing

31. Hearing • Neural perception of sound energy • Involves two aspects • Identification of the sounds (“what”) • Localization of the sounds (“where”) • Sound waves • Traveling vibrations of air • Consist of alternate regions of compression and rarefaction of air molecules

32. Hearing • Pitch (tone) of sound • Depends on frequency of air waves 20-20,000 cps, 1000-4000 • Intensity (loudness) • Depends on amplitude of air waves • Timbre (quality) • Determined by overtones

33. Hearing outline • Anatomy • Outer, middle, inner • hearing • Transmission of sound waves • Pitch and loudness • Hair cells and transduction • Cochlea and canals/ducts • auditory cortical processing

34. Transmission of Sound Waves • Tympanic membrane vibrates when struck by sound waves • Middle ear transfers vibrations through ossicles (malleus, incus, stapes) to oval window (entrance into fluid-filled cochlea) • Waves in cochlear fluid set basilar membrane in motion • Receptive hair cells are bent as basilar membrane is deflected up and down • Mechanical deformation of specific hair cells is transduced into neural signals that are transmitted to auditory cortex in temporal lobe of brain for sound perception

35. Fig. 6-33, p. 213

36. Hearing outline • Anatomy • Outer, middle, inner • Hearing • Transmission of sound waves • Pitch and loudness • Hair cells and transduction • Cochlea and canals/ducts • Auditory cortical processing

37. Inner • Deformation and rubbing on the tectoral membrane hyper or depolarizes the cells resulting in a signal. • Outer • Do not signal the brain • Fine tuning • Accentuates movement of basilar membrane • (lengthening and shortening) Transduction to Auditory nerve amplification Fig. 6-33c, p. 213

38. Fig. 6-34a, p. 214

39. Fig. 6-35, p. 215

40. Sound waves Bending of hairs of receptor hair cells of organ of Corti as basilar membrane move- ment displaces these hairs in relation to overlying tectorial membrane in which the hairs and embedded Vibration of tympanic membrane Vibration of middle ear bones Graded potential changes (receptor potential) in receptor cells Vibration of oval window Changes in rate of action potentials generated in auditory nerve Vibration of round window Fluid movement within cochlea In ear Dissipation of energy (no sound perception) Vibration of basilar membrane Propagation of action potentials to auditory cortex in temporal lobe of brain for sound perception Fig. 6-36, p. 216 Fig. 6-36, p. 216

41. Hearing outline • Anatomy • Outer, middle, inner • hearing • Transmission of sound waves • Pitch and loudness • Hair cells and transduction • Cochlea and canals/ducts • auditory cortical processing

42. Auditory Cortical Processing • Primary auditory cortex is tonotopically organized • Locations on basilar membrane map to locations in the cortex • Pathway • Hair cells-afferent auditory nerve- synapses in brainstem and thalamus (LGN)-higher auditory cortex

43. Cortex • Higher processing • Basal nuclei • Control of movement, inhibitory, negative • Thalamus • Relay and processing of sensory information • Awareness, a positive screening center for information • Hypothalamus • Hormone secretion, regulation of the internal environment • Cerebellum • Important in balance and in planning and executing voluntary movement • Brain Stem • Relay station (posture and equilibrium), cranial nerves, control centers, reticular integration, sleep control

44. Equilibrium outline • Anatomy • Semicircular canals • otoliths

45. Equilibrium • Vestibular apparatus • In inner ear • Consists of • Semicircular canals • Detect rotational acceleration or deceleration in any direction • Utricle and saccule • Detect changes in rate of linear movement in any direction • Provide information important for determining head position in relation to gravity

46. Fig. 6-38a, p. 219

47. Equilibrium • Neural signals generated in response to mechanical deformation of hair cells by specific movement of fluid and related structures • Vestibular input goes to vestibular nuclei in brain stem and to cerebellum for use in maintaining balance and posture, controlling eye movement, perceiving motion and orientation

48. Cortex • Higher processing • Basal nuclei • Control of movement, inhibitory, negative • Thalamus • Relay and processing of sensory information • Awareness, a positive screening center for information • Hypothalamus • Hormone secretion, regulation of the internal environment • Cerebellum • Important in balance and in planning and executing voluntary movement • Brain Stem • Relay station (posture and equilibrium), cranial nerves, control centers, reticular integration, sleep control

49. Equilibrium

50. Receptive hair cells Ampulla Cupula – moves in the Direction of movement Inertia! XYZ Kino – Stero-ionchannels Hair cells-affarent neurons-vestibular nerve-vestibulocochlear nerve- Fig. 6-38, p. 219