Slide 1 Sensory Receptors ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 2 Sensory Receptors ___________________________________ ÏRange from simple neurons to complex sense organs ___________________________________ ÏTypes: chemoreceptors, mechanoreceptors, photoreceptors, electroreceptors, magnetoreceptors, thermoreceptors ___________________________________ ÏAll transduce incoming stimuli into changes in membrane potential ___________________________________ ___________________________________ ___________________________________ Figure 7.1 ___________________________________ Slide 3 Sensory Receptors ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 7.1 ___________________________________ Slide 4 Classification of Sensory Receptors ___________________________________ ÏBased on stimulus location ÏTelereceptors – detect distant stimuli, e.g., ___________________________________ vision and hearing ÏExteroceptors – detect stimuli on the outside of the body, e.g., pressure and temperature ___________________________________ ÏInteroceptors – detect stimuli inside the body, e.g., blood pressure and blood oxygen ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 5 Classification of Sensory Receptors ___________________________________ ÏBased on type of stimuli the receptors can detect (stimulus modality) ___________________________________ ÏChemoreceptors – chemicals, e.g., smell and taste ÏMechanoreceptors – pressure and movement, e.g., touch, hearing, balance, blood pressure ___________________________________ ÏPhotoreceptors – light, e.g., vision; detect photons ÏElectroreceptors – electrical fields ÏMagnetoreceptors – magnetic fields ___________________________________ ÏThermoreceptors - temperature ___________________________________ ___________________________________ ___________________________________ Slide 6 Receptors and stimulus ___________________________________ ÏLocation: Can distinguish the location of the stimulus (touch, light or odour) ___________________________________ ÏDuration: Determine length of stimulus by responding to the stimulus for the duration ___________________________________ of the stimulus. ÏIntensity: Increase in action potential ___________________________________ frequency or increase in neurotransmitter release. ___________________________________ ___________________________________ ___________________________________ Slide 7 Sensitivity to Multiple Modalities ___________________________________ • Adequate stimulus – preferred or most sensitive stimulus modality • Many receptors can also be excited by other stimuli, if ___________________________________ sufficiently large, e.g., pressure on eyelid perceive bright light • Polymodal receptors – naturally sensitive to more than ___________________________________ one stimulus modality, e.g., ampullae of Lorenzini in sharks • Nociceptors – sensitive to strong stimuli, e.g., pain; many ___________________________________ are polymodal receptors ___________________________________ ___________________________________ ___________________________________ Slide 8 Stimulus Encoding ___________________________________ Ï All stimuli are ultimately converted into action potentials in the primary afferent neurons Ï How can organisms differentiate among stimuli or detect ___________________________________ the strength of the signal? Ï Sensory receptors must encode four types of information ___________________________________ ÏStimulus modality ÏStimulus location ÏStimulus intensity ___________________________________ ÏStimulus duration ___________________________________ ___________________________________ ___________________________________ Slide 9 Dynamic Range ___________________________________ • Action potentials code stimulus intensity through changes in frequency, e.g., strong stimuli high ___________________________________ frequency • Dynamic range –range of intensities for which receptors can encode stimuli ___________________________________ • Threshold detection – weakest stimulus that produces a response in a receptor 50% of the time ___________________________________ • Saturation – top of the dynamic range; all available proteins have been stimulated ___________________________________ ___________________________________ Figure 7.4a ___________________________________ Slide 10 Range Fractionation ___________________________________ Relationships between stimulus intensity and AP frequency • Linear across large range of intensities: large change in ___________________________________ stimulus causes a small change in AP frequency large dynamic range, poor sensory discrimination ___________________________________ • Linear across small range of intensities: small change in stimulus causes a large change in AP frequency small dynamic range, high ___________________________________ sensory discrimination Range fractionation – groups of receptors work together to increase dynamic range without decreasing sensory ___________________________________ discrimination ___________________________________ Figure 7.4b-c ___________________________________ Slide 11 Tonic and Phasic Receptors ___________________________________ Two classes of receptors that encode stimulus duration • Phasic – produce APs only at the beginning or end of the stimulus encode changes in stimulus, but not stimulus ___________________________________ duration • Tonic – produce APs as long as the stimulus continues • Receptor adaptation – AP frequency decreases if stimulus intensity is maintained at the same level ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 12 Tonic and Phasic Receptors, Cont. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 7.5 ___________________________________ Slide 13 Pain ___________________________________ • Pain and itching are mediated by Nocireceptors • Itch comes form Nocireceptors in the skin. Higher pathways for itch are not well understood ___________________________________ • Pain is s subjective perception ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 14 Chemoreception ___________________________________ • Most cells can sense incoming chemical signals • Animals have many types of chemoreceptors ___________________________________ • Multicellular organisms typically use taste and smell • Olfaction –sense of smell • Detection of chemicals carried in air ___________________________________ •Gustation– sense of taste • Detection of chemicals emitted from ingested food • Distinct due to structural criteria ___________________________________ • Performed by different sense organs • Use different signal transduction mechanisms ___________________________________ • Are processed in different integrating centers ___________________________________ ___________________________________ Slide 15 The Olfactory System ___________________________________ Evolved independently in vertebrates and insects Vertebrate olfactory system • Can distinguish thousands of odorants ___________________________________ • Located in the roof of the nasal cavity • Mucus layer to moisten olfactory epithelium • Odorant binding proteins – allow lipophilic odorants to dissolve in mucus • Receptor cells are bipolar neurons and are covered in cilia ___________________________________ • Odorant receptor proteins are located in the cilia ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 16 Odorant Receptors are G Proteins ___________________________________ • Each olfactory neuron expresses only one odorant receptor protein ___________________________________ • Each odorant receptor can recognize more than one odorant ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 7.7 ___________________________________ Slide 17 Pheromones ___________________________________ Vomeronasal organ –detects pheromones Structurally and molecularly distinct ___________________________________ from the primary olfactory epithelium • Location • Base of nasal cavity near the ___________________________________ septum in mammals • Palate in reptiles • Transduction ___________________________________ • Activates a phospholipase C- based signal transduction system; adenylate cyclase- cAMP in other olfactory ___________________________________ receptors ___________________________________ Figure 7.8 ___________________________________ Slide 18 Taste Buds in Vertebrates ___________________________________ Group of taste receptor cells Located on tongue, soft palate, larynx, and esophagus;