Chapter 39

1. Chapter 39

2. Learning Objectives • Describe sensory circuit • List five basic type of sensory receptors • Define sensation in neurological terms • Identify the role of each of the various mechanoreceptors for pressure, vibration, etc. • Explain the function of proprioceptors, electroreceptors and magnetoceptors

3. Learning Objectives • Describe how the ear transmits sound • Describe the morphology and function of the human eye • Define chemoreceptors • Map the human tongue and the process of taste • Diagram the human nasal cavity and the process of olfaction • Describe the function of nociceptors

4. Sensory Receptors(1) • Formed by endings of afferent neurons or specialized cells adjacent to neurons • Detect stimuli (various forms of energy) • Mechanical pressure • Sound waves • Light • Specific molecules or chemical conditions

6. Sensory Receptors(2) • Sensory transduction • Axons of afferent neurons carry action potentials generated by receptors to pathways leading to specific parts of the brain • Brain processes signals into sensory sensations

7. a. Sensory receptor formed by dendrites of an afferent neuron Stimulus Stimulus opens gated ion channels In sensory receptors formed by the dendrites of afferent neurons, a stimulus causes a change in membrane potential that generates action potentials in the axon of the neuron. Temperature and pain receptors are among the receptors of this type. Action potential Afferent neuron (to CNS) Dendrites forming sensory receptor Fig. 39.1a, p. 886

8. b. Sensory receptor formed by a cell that synapses with an afferent neuron Stimulus Sensory receptor cell or structure In sensory receptors consisting of separate cells, a stimulus causes a change in membrane potential that releases a neurotransmitter from the cell. The neuro-transmitter triggers an action potential in the axon of a nearby afferent neuron. Mechanoreceptors, photoreceptors, and chemoreceptors are examples of receptors of this type. Action potential Neurotransmitter or first messenger opens gated ion channels Diffusion of neurotransmitter or first messenger Fig. 39.1b, p. 886

9. Types of Receptors • 5 basic types • Mechanoreceptors • Photoreceptors • Chemoreceptors • Thermoreceptors • Nociceptors • Some animals have receptors that detect electrical or magnetic fields

10. Sensory Perception • Routing of information from sensory receptors to particular brain regions identifies a specific stimulus as a sensation • Intensity of a stimulus is determined by • Frequency of action potentials along neural pathways • Number of afferent neurons carrying action potentials

11. Sensory Adaptation • In many systems, frequency of action potentials decreases while a stimulus remains constant • Some sensory receptors (those related to tissue damage) show little or no sensory adaptation

12. 39.2 Mechanoreceptors and the Tactile and Spatial Senses • Receptors for touch and pressure occur throughout the body • Proprioceptors provide information about movements and position of the body

13. Mechanoreceptors • Detect mechanical energy • Touch, pressure, acceleration, vibration • Touch and pressure receptors • Free nerve endings • Encapsulated nerve endings of sensory neurons

14. 39.2 Mechanoreceptors and the Tactile and Spatial Senses • Receptors for touch and pressure occur throughout the body • Proprioceptors provide information about movements and position of the body

15. Mechanoreceptors • Detect mechanical energy • Touch, pressure, acceleration, vibration • Touch and pressure receptors • Free nerve endings • Encapsulated nerve endings of sensory neurons

16. 39.2 Mechanoreceptors and the Tactile and Spatial Senses • Receptors for touch and pressure occur throughout the body • Proprioceptors provide information about movements and position of the body

17. Mechanoreceptors: constant feedback on tactile senses • Detect mechanical energy • Touch, pressure, acceleration, vibration • Touch and pressure receptors • Free nerve endings • Encapsulated nerve endings of sensory neurons

18. Shaft of hair inside follicle Skin surface Epidermis Dermis Myelinated neuron Free nerve endings around hair root plexus Free nerve endings: light touch Pacinian corpuscle: deep pressure and vibrations Ruffini endings: deep pressure Meissner’s corpuscle: light touch, surface vibrations Fig. 39.2, p. 888

19. Proprioceptors: constant feedback on spatial position • Proprioceptors provide information about movements and position of the body • The vestibular apparatus of the human ear • Stretch receptors in muscles (muscles spindles) • Proprioceptors of tendons (Golgi tendon organs) for balance

20. Vestibular apparatus Anterior semicircular canal Posterior semicircular canal Utricle Saccule Lateral semicircular canal Fig. 39.5a, p. 890

21. Ampulla of a semicircular canal Direction of body rotation Endolymph pulls cupula in this direction Cupula Sensory hair cells Afferent neurons Fig. 39.5b, p. 890

22. Muscle Spindles and Golgi Tendon Organs

23. Hearing • Hearing relies on sensory hair cells in organs that respond to the vibrations of sound waves

24. Terrestrial Vertebrate Ear (1) • Outer ear (pinna) • Directs sound to the eardrum • Eardrum (tympanic membrane) • Transmits vibrations through one or more bones in the middle ear to the fluid-filled inner ear

25. Terrestrial Vertebrate Ear (2) • Middle ear • Malleus, incus, stapes • Oval window • Inner ear • Transmits vibrations through structures that bend stereocilia of hair cells • Cochelea, organ of Corti, round window • Bursts of action potentials determine frequency of sound waves

26. Semicircular canals Oval window (behind stapes) Stapes Auditory nerve Bone of skull Pinna Incus Malleus Eustachian tube leading to throat Round window Auditory canal Eardrum Cochlea Location of the human ear in the head Middle ear Inner ear Outer ear Internal structures of the outer, middle, and inner ear Fig. 39.8a, p. 893

27. 39.4 Photoreceptors and Vision • Vision involves detection and perception of radiant energy • Mammalian retinas contains rods and cones and a complex neuronal network • Three kinds of opsin pigments underlie color vision • The visual cortex processes visual information

28. Retina Cornea Lens Pupil Iris Fig. 39.11, p. 895

29. Photoreceptors of the Eye • Contain pigment molecules • Absorb energy of light • Generate changes in membrane potential • Retinal • Light-absorbing pigment in all animals

30. The Vertebrate Eye (1) • Cornea • Transparent, admits light • Iris • Behind the cornea • Controls diameter of pupil • Regulates amount of light that strikes the lens

31. The Vertebrate Eye (2) • Lens • Focuses image on the retina • Retina • Lines the back of the eye • Photoreceptors and neurons integrate information detected by photoreceptors

32. Sclera Retina Choroid Ciliary body Fovea Iris Blind spot Lens Pupil Cornea Part of optic nerve Aqueous humor Ciliary muscle Vitreous humor Fig. 39.12, p. 896

33. Focus • In birds, mammals, and most reptiles, light is focused on the retina by the combined effect of the cornea and adjusting lens shape

34. Fig. 39.13a, p. 896

35. Fig. 39.13b, p. 896

36. Region of overlap of the two visual fields Visual field of left eye Visual field of right eye Region of overlap of two visual fields Right eye Left eye Optic nerve Optic chiasm Lateral geniculate nucleus of the thalamus Visual cortex Fig. 39.17, p. 900

37. Photoreceptors of the Retina • Rods • Specialized for detection of low-intensity light • Cones • Specialized for detecting light of different wavelengths (colors)

38. Photopigment Molecules • Absorb light in photoreceptor cells • Consist of retinal combined with an opsin protein • 3 photopigments (photopsins) Pigment absorbs light, retinal changes form • Reactions alter amount of neurotransmitter released by photoreceptor cells

39. a. Structure of cones and rods Cone Rod Discs Back of retina Light-absorbing photopigment Outer segment Outer segment Discs (houses discs that contain light-absorbing photopigment) Inner segment Inner segment (houses cell’s metabolic machinery) Synaptic terminal Synaptic terminal (stores and releases neurotransmitters) Front of retina Fig. 39.14a, p. 897

40. b. How rhodopsin functions Rhodopsin in the dark (inactivated) Rhodopsin in the light (activated) Light absorption Retinal changes shape Enzymes cis-Retinal trans-Retinal Fig. 39.14b, p. 897

41. The Retina and Visual Processing • Rods (low light) and cones( bright and color) • Linked to neurons in the retina • Perform initial integration and processing of visual information • Processed signal is sent via the optic nerve through the lateral geniculate nuclei to the visual cortex

42. Color-blindness • Genetic disorder • 8% males, 0.5% females • Red-green is most common • Type of color deficiency depends on wavelength of light that is not being detected (long, medium, or short wavelength detecting cone).

43. Retina: Initial Integration

44. Chemoreceptors • Chemoreceptors respond to the presence of specific molecules in the environment • In vertebrates, they form parts of receptor organs for taste (gustation) and smell (olfaction)

45. Taste Receptors • Detect molecules from food or other objects that come into direct contact with the receptor • Are used primarily to identify foods

46. Taste bud Papilla (cutaway) Sensory hair of taste receptor Papillae Tongue Afferent nerve Taste buds Papilla Fig. 39.20, p. 902

48. Olfactory tract from receptors to the brain Olfactory bulb Nasal cavity Bone Olfactory receptors Supporting cells Sensory hairs of olfactory receptors Mucus Fig. 39.21, p. 902

49. 39.6 Thermoreceptors and Nociceptors • Thermoreceptors occur in warm and cold forms • Nociceptors protect animals from potentially damaging stimuli

50. Nociceptors • Detect stimuli that can damage body tissues • Located on body surface and interior • Information from receptors is integrated in the brain into the sensation of pain