Chapters 8 and11: Nonvisual Sensory Systems

1. Chapters 8 and11: Nonvisual Sensory Systems

2. Sensory Systems • The brain detects events in the external environment and directs the corresponding behavior • Afferent neurons carry sensory messages to brain • Efferent neurons carry motor messages to the muscles • Stimulus: any energy capable of exciting a receptor. This defines broad categories of sensory systems • Mechanical • Chemical • Thermal • Photic

3. Introduction • Sensory Systems • What is the energy and how is it transduced? • What is the pathway to brain? • What common features does it share with other sensory systems?

4. Introduction: Chemoreceptors (gustatory and olfaction) • Animals depend on the chemical senses to identify nourishment • Chemical sensation • Oldest and most common sensory system • Chemical senses • Gustation • Olfaction • Chemoreceptors

5. Taste • The Basics Tastes • Saltiness, sourness, sweetness, bitterness, and umami • Examples of correspondence between chemistry • Sweet—sugars like fructose, sucrose, artificial sweeteners (saccharin and aspartame) • Bitter—ions like K+ and Mg2+, quinine, and caffeine • Advantage – Survival • Poisonous substances - often bitter

6. Taste • The Basic Tastes • Steps to distinguish the countless unique flavors of a food • Each food activates a different combination of taste receptors • Distinctive smell • Other sensory modalities

7. Taste • The Organs of Taste • Tongue, mouth, palate, pharynx, and epiglottis

8. Taste • The Organs of Taste • Areas of sensitivity on the tongue • Tip of the tongue • Sweetness • Back of the tongue • Bitterness • Sides of tongues • Saltiness and sourness

9. Taste • The Organs of Tastes • Taste receptors • Threshold concentration • Just enough exposure of single papilla to detect taste

10. Taste • Tastes Receptor Cells • Apical ends Microvilli Taste pore • Receptor potential: Voltage shift

11. Taste • Taste Receptor Cells

12. Taste • Mechanisms of Taste Transduction • Transduction process • Taste stimuli (tastants) • Pass directly through ion channels • Bind to and block ion channels • Bind to G-protein-coupled receptors

13. Taste • Mechanisms of Taste Transduction • Saltiness • Salt-sensitive taste cells • Special Na+ selective channel • Blocked by the drug amiloride

14. Taste • Mechanisms of Taste Transduction • Sourness • Sourness- acidity – low pH • Protons causative agents of acidity and sourness

15. Taste • Mechanisms of Taste Transduction • Bitterness • Families of taste receptor genes - TIR and T2R

16. Taste • Mechanisms of Taste Transduction • Sweetness • Sweet tastants natural and artificial • Sweet receptors • T1R2+T1R3 • Expressed in different taste cells

17. Taste • Mechanisms of Taste Transduction • Umami • Umami receptors: • Detect amino acids • T1R1+T1R3

18. Taste • Central Taste Pathways • Gustatory nucleus • Point where taste axons bundle and synapse • Ventral posterior medial nucleus (VPM) • Deals with sensory information from the head • Primary gustatory cortex • Receives axons from VPM taste neurons

19. Taste • Central Taste Pathways (Cont’d) • Localized lesions • Ageusia- the loss of taste perception • Gustation • Important to the control of feeding and digestion • Hypothalamus • Basal telencephalon

20. Taste • The Neural Coding of Taste • Labeled line hypothesis • Individual taste receptor cells for each stimuli • In reality, neurons broadly tuned • Population coding • Roughly labeled lines • Temperature • Textural features of food

21. Difference between smell and pheromones? Smell (Olfactory)— a mode of communication • Important signals • Reproductive behavior • Mate Selection • Territorial boundaries • Identification • Aggression • Pheromones • Mate Selection • Territorial boundaries • Identification • Aggression • Role of human pheromones

22. Pheromone Actions in Animals • Pheromones are chemicals that transmit a message from one animal to another • Pheromones can alter reproduction • Lee-Boot effect: the estrous cycle stops when groups of female mice are housed together • Whitten effect: the estrous cycle restarts in synchrony when a group of female mice are exposed to the urine of a male mouse • Bruce effect: involves the failure of pregnancy when a recently impregnated mouse is exposed to a normal male mouse (other than the one with which she mated) • The vomeronasal organ detects nonvolatile chemicals in urine • The vomeronasal organ projects to the accessory olfactory bulb which in turn projects to the amygdala which has connections with the hypothalamus • Lesions of the accessory olfactory bulb disrupt the Lee-Boot, Whitten and Bruce effects

23. Pheromone Actions in Humans • Humans possess a vomeronasal organ • Exposure to chemical present in sweat can alter human behavior • McClintock studied the menstrual cycles of women who attended an all-female college • Women who spent time together showed synchronization of their menstrual cycles • Women who spent time with men showed shorter cycles • Exposure to underarm sweat elicited synchronization • Pheromones present in human sweat can alter social behavior • Androstenol placed on a necklace had no effect on the social interactions of men, but women exposed to androstenol showed more interactions with me

24. Smell • The Organs of Smell • Olfactory epithelium • Olfactory receptor cells, supporting cells, and basal cells

25. Smell • The Organs of Smell • Odorants: Activate transduction processes in neurons • Olfactory axons constitute olfactory nerve • Cribriform plate: A thin sheet of bone through which small clusters of axons penetrate, coursing to the olfactory bulb • Anosmia: Inability to smell • Humans: Weak smellers • Due to small surface area of olfactory epithelium

26. Smell • Olfactory Receptor Neurons • Olfactory Transduction

27. Smell • Olfactory Signal • Adaptation: Decreased response despite continuous stimulus

28. Smell • Central Olfactory Pathways

29. Smell • Central Olfactory Pathways (Cont’d)

30. Smell • Central Olfactory Pathways (Cont’d) • Axons of the olfactory tract: Branch and enter the forebrain • Neocortex: Reached by a pathway that synapses in the medial dorsal nucleus

31. Smell • Spatial and Temporal Representations of Olfactory Information • Olfactory Population Coding • Olfactory Maps (sensory maps) • Temporal Coding in the Olfactory System • Olfaction paradox

32. Concluding Remarks • Transduction mechanisms • Gustation and olfaction • Similar to the signaling systems used in every cell of the body • Common sensory principles - broadly tuned cells • Population coding • Sensory maps in brain • Timing of action potentials • May represent sensory information in ways not yet understood

33. The Nature of Sound • Sound • Audible variations in air pressure • Sound frequency: Number of cycles per second expressed in units called Hertz (Hz) • Cycle: Distance between successive compressed patches • Range: 20 Hz to 20,000 Hz • Pitch: High and Low • Intensity: Difference in pressure between compressed and rarefied patches of air

34. The Structure of the Auditory System • Auditory System

35. The Structure of the Auditory System • Auditory pathway stages • Sound waves • Tympanic membrane • Ossicles • Oval window • Cochlea fluid • Sensory neuron response • Brain stem nuclei output • Thalamus to MGN

36. The Middle Ear • Components of the Middle Ear

37. Tonotopic Mapping

38. Sound Force Amplification by the Ossicles Pressure: Force by surface area Greater pressure at oval window than tympanic membrane, moves fluids The Attenuation Reflex Response where onset of loud sound causes tensor tympani and stapedius muscle contraction Function: Adapt ear to loud sounds, understand speech better The Middle Ear

39. The Inner Ear • Physiology of the Cochlea • Pressure at oval window, pushes perilymph into scala vestibuli, round window membrane bulges out • The Response of Basilar Membrane to Sound • Structural properties: Wider at apex, stiffness decreases from base to apex • Research: Georg von Békésy • Endolymph movement bends basilar membrane near base, wave moves towards apex

40. The Inner Ear • The Organ of Corti and Associated Structures

41. The Inner Ear • Transduction by Hair Cells • Research: A.J. Hudspeth. • Sound: Basilar membrane upward, reticular lamina up and stereocilia bends outward

42. Central Auditory Processes Auditory Pathway • Primary pathway: Ventral cochlear nucleus to superior olive to inferior colliculus to MGN to auditory cortex

43. Auditory Cortex • Principles in Study of Auditory Cortex • Tonotopy, columnar organization of cells with similar binaural interaction • The Effects of Auditory Cortical Lesions and Ablation • Lesion in auditory cortex: Normal auditory function (like vision?) • Lesion in striate cortex: Complete blindness in one visual hemifield • Different frequency band information: Parallel processing, localization deficit

44. Concluding Remarks • Hearing and Balance • Auditory Parallels Visual System • Tonotopy (auditory) and Retinotopy (visual) preserved from sensory cells to cortex code • Convergence of inputs from lower levels  Neurons at higher levels have more complex responses

45. Chapter 12: The Somatic Sensory System

46. Introduction • Somatic Sensation • Enables body to feel, ache, chill • Sensitive to stimuli • Responsible for feeling of touch and pain • Somatic sensory system: Different from other systems • Receptors: Distributed throughout • Responds to different kinds of stimuli

47. Touch • Types and layers of skin • Hairy and glabrous (hairless) • Epidermis (outer) and dermis (inner) • Functions of skin • Protective function • Prevents evaporation of body fluids • Provides direct contact with world • Mechanoreceptors • Most somatosensory receptors are mechanoreceptors

48. Touch • Mechanoreceptors (Cont’d) • Pacinian corpuscles • Ruffini's endings • Meissner's corpuscles • Merkel's disks • Krause end bulbs

49. Touch • Mechanoreceptors (Cont’d) • Receptive field size and adaptation rate

50. Touch • Mechanoreceptors (Cont’d) • Two-point discrimination • Importance of fingertips over elbow • Primary Afferent Axons • Aa, Ab, Ad, C • C fibers mediate pain and temperature • Ab mediates touch sensations