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10/25/16 Some updates to original. I will probably update more later Five sensory modalities recognized since ancient times • • • • • Vision Hearing Touch Taste Smell Ideal Sensory Receptor Response Stimulus •Rapid response •Large amplitude •Rapid recovery •Steady baseline Important Features for Sensory Receptor Cell Function • High Sensitivity • Adaptation • Receptors code relative stimulus, not absolute size advantages of ionotropic vs metabotropic signaling “Ionotropic versus Metabotropic” Sensory Receptors Fast Amplification Response Stimulus A A* B A A* B* Notice anything strange given what he just said about an ideal receptor? C C* Which fire action potentials • • • • • Photoreceptors Olfactory receptor neurons Inner hair cells Outer hair cells Pain sensing neurons in your arm Which fire action potentials • • • • • Photoreceptors Olfactory receptor neurons Inner hair cells Outer hair cells Pain sensing neurons in your arm Signaling is metabotropic in which of the following • Photoreceptors • Olfactory receptor neurons • Hair Cells Signaling is metabotropic in which of the following • Photoreceptors • Olfactory receptor neurons • Hair Cells Ions responsible for depolarization • Hair cells • Olfactory receptor neurons • Photoreceptors Ions responsible for depolarization • Hair cells Mostly K, also Ca • Olfactory receptor neurons Na, Ca, Cl • Photoreceptors Na,Ca Does the base of the basilar membrane respond to high or low frequencies? Width greater at base or apex? More stiff at base or apex? Does the base of the basilar membrane respond to high or low frequencies? High Width greater at base or apex? apex More stiff at base or apex? base Cochlea Sound Frequency Tuning Know that this is called tonotopic mapping Does deflection of stereocilia towards the kinocilium depolarize or hyperpolarize hair cells? What experiment was done to show this? Deflection of Hair Cell Bundle Towards Kinocilium Causes Depolarization Towards the kinocilium is moving in the direction where the little hairs get taller. Describe two experiments you could do to find the preferred frequency (characteristic frequency) of a hair cell Hair Cells Frequency Tuning can you explain the oscillation stuff in hair cells with channels and stuff Voltage- and Calcium-Activated Channels Shape Hair Cell Voltage Responses Tuning Frequency and K+ Conductance Inner vs outer hair cells sorry these are poorly phrased, but hopefully you get the point • Which type of hair cell is primarily responsible for hearing • Which type of hair cell is primarily responsible for tuning • Which type of hair cell provides most afferent input to the brain • Which type of hair cell receives efferent input from the brain Inner vs outer hair cells sorry these are poorly phrased, but hopefully you get the point • Which type of hair cell is primarily responsible for hearing – Inner. These are the hair cells that actually carry sound information. • Which type of hair cell is primarily responsible for tuning – Outer. Outer hair cells can change shape to damp movement of the membrane, or amplify oscillations at certain frequencies. • Which type of hair cell provides afferent input to the brain – Inner. If you do not know what afferent means, google it. This should make sense. • Which type of hair cell receives more efferent input from the brain – Outer. If you do not know what efferent means, google it. This should make sense. Channels responsible for the depolarization of olfactory receptor neurons are gated by Channels responsible for the depolarization of olfactory receptor neurons are gated by • Cyclic nucleotides (cAMP) • There are also Ca activated chloride channels. Signal Transduction in Olfactory Neurons How would depletion of extracellular Na+ influence the olfactory receptor neuron response? How would depletion of extracellular Na+ influence the olfactory receptor neuron response? • The response would be reduced, but the cell would still respond because you would still get calcium influx and activation of Ca gated chloride channels which depolarize ORNs Signal Transduction in Olfactory Neurons Signal Transduction in Olfactory Neurons SITS is a chloride channel blocker Which ion is important for adaptation in olfactory receptor neurons Which ion is important for adaptation in olfactory receptor neurons • Calcium. Always calcium Adaptation of the Olfactory Neurons Why do you think they normalized the responses? Where are the receptors located Signal Transduction in Olfactory Neurons Here Not here Taste Taste transduction Vertebrate photoreceptors release • • • • Glutamate GABA Glycine Depends on whether they are part of the ON or OFF pathway Vertebrate photoreceptors release • • • • Glutamate GABA Glycine Depends on whether they are part of the ON or OFF pathway Channels responsible for the depolarization of photoreceptors in vertebrates are gated by Channels responsible for the depolarization of photoreceptors in vertebrates are gated by • Cyclic nucleotides (cGMP) – Remember that in ORNs it was cAMP Cyclic GMP-Gated Channels The vertebrate photoresponse can be described as a • • • • Conductance increase EPSP Conductance decrease EPSP Conductance increase IPSP Conductance decrease IPSP • None of these. Why are you calling it a post synaptic potential if we aren’t talking about synaptic transmission – Sorry. That’s true but the important stuff I am trying to point out is still the same The vertebrate photoresponse can be described as a • • • • Conductance increase EPSP Conductance decrease EPSP Conductance increase IPSP Conductance decrease IPSP – Photoreceptors have a constant inward current in the dark. When they are activated by light, these channels close and photoreceptors hyperpolarize. Notice that the photoresponse is reduction of an inward current Inward current at rest Reduction of inward current light Dark Current is Suppressed by Light • If you were given – – – – – Rhodopsin Transducin PDE cGMP/GMP CNG channel could you give a brief outline of the rod photoresponse Baylor 1996 • Rods can respond to a single photon of light. Which steps in the previous thing are sites of amplification Calcium and Photoreceptor Adaptation Baylor 1996 Losing which would be most damaging for your ability to see a wide range of wavelengths • S-Cones • M-Cones • L-Cones Losing which would be most damaging for your ability to see a wide range of wavelengths • S-Cones Less overlap with other types of photoreceptors Photoreceptor Spectral Tuning In humans there are two blind spots for rod vision. What/where are they? In humans there are two blind spots for rod vision. What/where are they? • Optic disk – where RGC axons exit the retina • Fovea – There are only cones in the fovea Rod Cone Distribution in Human Retina Cross section through human fovea What are some differences between rods and cones Rod and Cone Photoreceptors Rods: A. High Sensitivity B. Slow Response C. Monochromatic Cone Opsin Cones: A. Low Sensitivity B. Faster Responses C. Color Vision Be careful with the ones in boxes. If he asks a test question about differences in phototransduction between rods and cones, C is not an answer. Color vision comes from having multiple cones that preferentially respond to different wavelengths. Photocurrent (pA) Comparison of Rod and Cone Physiology CONE ROD 0 0 -5 -20 -10 -40 -15 0 4 8 12 0 4 t (s) 8 12 t (s) ROD CONE Normalized Response 1.0 0.5 0.0 1 10 2 10 3 10 PIGM* / cell 4 10 5 10 Which ion is important for adaptation in photoreceptors Which ion is important for adaptation in photoreceptors • It is always calcium – We will talk about why/how next week Calcium and Photoreceptor Adaptation Baylor 1996 Photoreceptor Responses to Light Light Adaptation Reduces Cone Sensitivity Dark 1.0 8.8 X 103 0.8 R/Rmax 4.0 X 104 0.6 0.4 0.2 0.0 1 2 3 4 Log Light Intensity 5 6