Sensory Physiology

1. Sensory Physiology Chapter 13

2. Sensors • Detect changes in environmental conditions • Primary Sensors • neurons modified to undergo action potentials in response to specific stimuli (e.g. chemical, mechanical) • Secondary Sensors • Cells that respond to environmental change by releasing neurotransmitters to neurons

3. Transduction • Conversion of environmental change into an electrical signal • Receptor responds to stimulus by • opening ion channels (primary sensors) • releasing neurotransmitter to a neuron (secondary sensors) • receptor potential (graded) • Lead to action potential formation in sensory neurons • Rate of AP generation is proportional to stimulus strength Fig 13.3

4. Types of Environmental Stimuli • Chemoreception • Mechanoreception • Electromagnetic Reception

5. Chemoreception • Detection of chemical types and concentrations • Gustation (Taste) • chemicals in contact with the animal • Olfaction (Smell) • chemicals concentrated at a distance • Internal Chemoreceptors (PO2, PCO2, pH)

6. Taste Buds (Contact Chemoreceptors) • Detect chemicals from sources in contact with animal • Contain microvilli that project to the external surface • Chemicals come into contact with these hairs • Release neurotransmitter to sensory neurons • Action potentials are generated in neuron Figs 13.32, 13.33

7. Olfactory Receptors(Distance Receptors) • Detection chemicals from distant sources • Modified neurons • receptors located in nasal epithelium in the nasal cavity • Have hair-like projections that respond to chemicals in air Fig 13.35

8. Squamate Tongues • Tongue collects chemicals then retracts • swab chemicals over vomeronasal organ (Jacobson’s organ) • chemical perception • forked tongue gives directional perception

9. Insect Antennae • Pheromonal Reception

10. Mechanoreception • Detection of Mechanical Energy and Force • Tactile (touch and pressure) • Proprioception (movement, body position) • Equilibrium (gravity and acceleration) • Vibrations (sound)

11. Tactile Receptors • Insect cuticular receptors • Bristle/hair receptors • Vertebrate cutaneous receptors • Expanded dendritic endings • Ruffini endings and Merkel's disks • Touch • Encapsulated endings • Meissner's corpuscles, Krause's corpuscles, Pacinian corpusles • Pressure Fig 13.5

12. Proprioceptors • Detect changes in length and tension of the muscles Figs 13.3, 13.24

13. Equilibrium:Hair Cells • located deep inside the ear • vibrations bend “hairs” (stereocilia) • opens/closes physically gated ion channels • alters release of neurotransmitter to sensory neurons Fig 13.27

14. Equilibrium:Invertebrate Statocysts • Central statolith stimulates different hair cells based on orientation to gravity Fig 13.25

15. Equilibrium:Vertebrate Vestibular Organs • Fluid-filled compartments in the inner ear • Semi-circular canals • Rotation of the head • Otolith organs • linear movement of head and orientation relative to gravity Fig 13.26

16. Vibration • Vertebrate Cochlea • Elongate structure containing hair cells • Fluid pressure waves induce vibration of the basilar membrane • Stimulates hair cells Figs 13.28-13.30

17. Vibrations:Insect “Ears” • Tympanic Organs • Terminal Cerci • Johnston’s organ • Wind receptor • May be tuned to specific frequencies Fig 10.3

18. Vibrations:Lateral Lines • Fish and aquatic amphibians • Hair cells distributed along lateral line • Detect vibrations in water and flow of water Animation: http://www.blackwellpublishing.com/matthews/haircell.html

19. Electromagnetic and Thermal Perception • Vision • Temperature • Electric • Magnetism

20. Vision • Perception of electromagnetic radiation • portion of the EM spectrum Fig 13.10

21. Advanced Eyes:Refraction of Light • Light refracted by transparent/translucent structures • bending of light leads to projection of focused image on the retina Fig 13.11

22. Vertebrate Photoreceptors • rods - light intensity • cones - color • Each photoreceptor has two segments • Inner segment • metabolic machinery • synaptic endings • Outer segment • contains layers of internal membranes containing photopigments Figs. 13.12, 13.13, 13.22

23. Transduction of Light • Cells change metabolic activity with activation of photopigments • Stimulate sensory neurons Figs. 13.11, 13.13, 13.14

24. Compound Eyes (Arthropods) • Consist of many ommotadia • Each with lens and photoreceptor cells • E.g., Green, Blue, Ultraviolet in honeybees • Images from many ommotadia processed into a single visual picture Fig 13.23

25. Thermal Perception • Modified neurons • E.g. cutaneous heat and cold receptors • Thermosensory pits (snakes) • Detect heat from warm prey, thermal conditions in habitat

26. Electroreception • Marine elasmobranchs • ampullae of Lorenzini • detect electrical fields generated by other fish • Freshwater teleosts • caudal electric organs • generates electrical field around animal • objects near animal alter electric field • detected by cells in lateral line • Platypus • Mucous/serous gland electroreceptor • Neurons surround pores of mucous and serous glands Fig 13.37

27. Magnetic Field Perception • Long distance orientation • Follow the earth’s magnetic field • Mechanism (?) • Magnetite (Fe3O4) present in various receptor cell types • Photoreceptors – birds, salamanders • Electroreceptors – elasmobranchs • Olfactor receptors - trout Figs 16.8-16.9