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Lecture21 - BioNB222 Cornell University Spring 2008 Carl D...

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BioNB222 Spring 2008 Cornell University Carl D. Hopkins 1 Lecture 21. Sensory Transduction Sensory transduction occurs when some form of external energy such as chemical, mechanical, or light is converted into a neuro-electric event that can be used for neural signaling. In this lecture we will attempt to unify the diverse sensory transduction mechanisms into three basic types: G-protein coupled receptors, ion-channel receptors, and mechanically-linked ion channels. Sensory transduction thus is considered from the point of view of molecular machinery at the level of membranes. The objective is for students to understand how different sensory systems each employ variants on these three basic themes, while each achieves neuronal activation in response to an external energy. Reading Assignment Purves et al. 4 th ed (2007) pp. 234 (box); 264-269; 327-330; 346-7 (box); 372-378; 387- 389. The reading material for this lecture is dispersed among the various chapters on pain reception, vision, hearing, olfaction, and taste. Please read the assigned pages looking to integrate the topics according to the learning objectives listed above. Learning Objectives Students should be able to: 1) Identify the precise anatomical location of sensory transduction in the following types of sensations: hearing, touch on the hand, pain, light, taste. Where are the sensory transduction molecules located? Is transduction taking place in a specialized “receptor cell” or in a nerve ending of a sensory nerve fiber? 2) Make a list of all of the sensory modalities listed above and be able to define the molecular transducers in each case. 3) For vision and for smell, define the sequence of biochemical steps that lead from transduction to opening or closing an ion channel. 4) What are some of the sensory transducers for which the transduction mechanism is unknown? Introduction Neurons are normally activated in two ways, either by synaptic inputs from other neurons, which we have already discussed extensively, or by sensory receptor activation. These six lectures focus on sensory mechanisms, highlighting vision, hearing, and olfaction. Animals are sensitive to a wide range of Fig. 1. Different types of sensory receptor cells found in vertebrates. Sensory stimuli act at sites indicated by the small arrows. Stippling indicates ares were transduction/synaptic transmission takes place. Large arrows indicate the site of impulse initiation (From: Shepherd, G. M. 1983. Neurobiology. Oxford Univ. Press, Oxford, Fig. 11.1, p 191.) (Shepherd, 1983)
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BioNB222 Spring 2008 Cornell University Carl D. Hopkins 2 Fig. 3 Bipolar ORN in olfactory epithelium. (From Cajal, 1909) (Ramón y Cajal, 1909) environmental stimuli through the action of their sense organs. Traditionally each of the sensory system was thought to depend upon a very characteristic and specialized type of sensory receptor cell that responds to stimulation and that activates neurons that ultimately lead to a response (Fig. 1).
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