Slide 1 Sensory Receptors ______

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Slide 2 Sensory Receptors ______ÏRange from simple to complex organs ______ÏTypes: chemoreceptors, , 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 location ÏTelereceptors – detect distant stimuli, e.g., ______vision and 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 ______

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Slide 5 Classification of Sensory Receptors ______ÏBased on type of stimuli the receptors can detect (stimulus ) ______ÏChemoreceptors – chemicals, e.g., smell and ÏMechanoreceptors – pressure and movement, e.g., touch, hearing, balance, blood pressure ______ÏPhotoreceptors – , e.g., vision; detect ÏElectroreceptors – electrical fields ÏMagnetoreceptors – magnetic fields ______ÏThermoreceptors - temperature ______

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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 ______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 ______

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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 ______

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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 – AP frequency decreases if stimulus intensity is maintained at the same level ______

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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 . Higher pathways for itch are not well understood ______• Pain is s subjective ______

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Slide 14 Chemoreception ______• Most cells can sense incoming chemical signals • Animals have many types of chemoreceptors ______• Multicellular organisms typically use taste and smell • Olfaction – • 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 ______

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Slide 15 The ______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 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 • 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 , soft palate, larynx, and esophagus; external surface of the body in some fish ______

______Slide 19 Taste Buds in Vertebrates ______Ï 50 to 150 taste cells Ï Epithelial cells that have apical and basal sides and joined by tight junctions ______Ï Life span of 10-14 days Ï Basal stem cells divide to regenerate taste cells Ï Microvilli on its apical surface that project into the mucus of the tongue Ï Taste receptor proteins are found in the microvilli ______Ï Chemicals are soluble and diffuse to the bind to their receptors Ï Different cells in the same bud can detect NaCl, sucrose, H+ and quinine (bitter) Ï Taste cell forms a chemical synapse with a that projects ______to the from the tongue ______

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Slide 20 Taste buds and peripheral innervation ______Figure 7.11c-d ______

Slide 21 A generic taste cell. ______ÏApical surface: both channels and G-protein- coupled receptors that are activated by chemical stimuli ÏBasolateral surface: voltage-gated Na+, K+, ______and Ca2+ channels, as well as all the machinery for synaptic transmission mediated by serotonin ÏThe increase in intracellular Ca2+ is either by ______the activation of voltage-gated Ca2+ channels or via the release from intracellular stores causes synaptic vesicles to fuse and release their transmitter onto receptors on primary ______sensory neurons ÏEach cell contains the standard complement of neuronal proteins including Na+/K+ ATPase at the basal level, voltage-gated Na+ ______and Ca2+ channels, leak K+ channel ______

______Slide 22 A generic taste cell…cont. ______ÏThe response to the chemical is mediated by the expression of receptors for that chemical in the microvilli ______ÏThe response is a depolarization of the cell sometimes enough to generate an action potential ÏThe signaling of the cell to the sensory ______neuron depends on a sufficient depolarization to open the voltage-gated Ca2+ channels necessary for vesicle fusion and neurotransmitter release. ______

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Slide 23 Transduction mechanisms ______

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Slide 24 G-Protein-Coupled Receptors ______

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______Slide 25 G-protein and adenylate cyclase ______

* * * * ______* * * ______* * ______* * * ______* * ______

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Slide 26 The inositol-phospholipid signaling pathway ______You don’t have to memorize this ☺ weeeeeee but be aware of it and know which taste is transmitted using this pathway ie bitter ______

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Slide 27 Salt taste ______Ï The Na+ enters into the cell through the passive amiloride-sensitive Na+ channel Ï These proteins are found in frog skin and kidney ______Ï Amiloride will block Na+ salt taste reception Ï Entry of Na+ into the cell of course causes the cell to depolarize ______Ï Need a large concentration of Na+ to trigger a sufficient depolarization to signal to the post- synaptic sensory neuron ______

______Slide 28 Salt taste ______* ______* ______* ______

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Slide 29 Sour taste ______Taste response produced by acids, excess protons (H+). These positive ions enter the cell through a H+, cation specific ion channel and in turn depolarize the cell to threshold for an action potential. ______

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Slide 30 Sour taste ______* * ______* ______* ______

______Slide 31 Sweet taste ______ÏThere are specific membrane receptors for different sweeteners and sugars ÏThese receptors are not ligand gated ion channels but rather are metabotropic receptors ÏThese receptors belong to the family of seven transmembrane domain ______proteins that are linked to signaling cascades through G proteins. In mammals a combination of the T1R2/T1R3 receptors have a response to sugars and sweeteners ÏThese receptors stimulate a G protein (Gp) which in this case activates ______phosopholipase C (PLC) ÏPLC breaks down PIP2 (phosphatidylinositol 4,5-bisphosphate) into IP3 (inositol triphosphosphate) and DAG ÏIP3 will bind to and activate a ion channel (TRP channel called TRPM5) ______which allows Ca2+ to influx into the cell ÏThis pathway leads to a depolarization and threshold is reached to trigger an action potential ______

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Slide 32 Sweet taste ______• In other animals sugars also appear to bind to receptors that stimulate G proteins (Gs) that activate adenylate cyclase • This results in an increase in cAMP in the cell that activates a protein kinase (PKA) which in turn phosphorylates a K+ channel to close the ______channel • Once the K+ channel is close the cell will depolarize ______

• Both these signaling cascades are used in multiple biological systems • In the nervous system neurotransmitter binding to specific metabotropic ______receptors can trigger these cascades • Photoreceptor and olfactory neurons also use parts of these cascades for their sensory transduction ______

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Slide 33 Sweet taste ______* * * * ______* ______* ______

______Slide 34 Bitter taste ______Different cells have different mechanisms of bitter taste transduction 1. In mammals the bitter receptor is a metabotropic receptor called T2R. There are about 30 different subtypes in mammals These signal through a G protein called gustducin to PLC and thus ______generate IP3 Like sweet receptors the IP3 activates a TRPM5 channel to open and allow Ca2+ to influx into the cell. 2. Some bitter chemicals such as quinine bind to and block specific K+ ______channels and thus result in depolarization of the cell ______

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Slide 35 Bitter taste ______* * * ______* ______

* ______

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Slide 36 Amino acid taste cells ______In some animals (catfish) there are a high number of amino acid taste cells There appears to be multiple ways that animals respond to amino aicds 1. In fish and other amphibians, amino acids such as L-arginine and L- proline bind to specific receptors which are ligand gated ion channels ______2. In mammals there are taste cells that respond to L-glutamate. In these cells L-glutamate activates a metabotropic receptor glutamate receptor linked to a G protein. Glutamate binds to many different metabotropic receptors and in taste cells it is the mGluR4 that is responsible for the ______taste transduction 3. In mammals there are also two metabotropic receptors T1R1/T1R3 that combine to respond to the standard 20 amino acids. This combination signals through G protein activation of PLC and the generation of IP3 ______and the activation of the TRPM5 channel. ______

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