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Chapter 50 biology notes outline - Chapter 50 Sensory and...

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Chapter 50 Sensory and Motor Mechanisms Lecture Outline Overview: Sensing and Acting The origins of sensing date back to the appearance in prokaryotes of cellular structures that sense pressure and chemicals in the environment and direct movement in an appropriate direction. These structures have been transformed during the course of evolution into diverse mechanisms that sense various types of energy and generate many different levels of physical movement in response. The detection and processing of sensory information and the generation of motor output provide the physiological basis for all animal behavior. Concept 50.1 Sensory receptors transduce stimulus energy and transmit signals to the central nervous system The brain’s processing of sensory input and motor output is cyclical rather than linear. Sensing, brain analysis, and action are ongoing and overlapping processes. Information is transmitted through the nervous system in the form of all-or-nothing action potentials. What matters is where action potentials go. Sensations begin as different forms of energy detected by sensory receptors. This energy is converted to action potentials that travel to appropriate regions of the brain. Once the brain is aware of sensations, it interprets them, giving the perception of stimuli. Perceptions such as colors, smells, sounds, and tastes are constructions formed in the brain and do not exist outside of it. Sensory receptors transduce stimulus energy and transmit signals to the nervous system. Sensory reception begins with the detection of stimulus energy by sensory receptors. Most sensory receptors are specialized neurons or epithelial cells that exist singly or in groups with other cell types in sensory organs, such as eyes or ears. Exteroreceptors detect stimuli originating outside the body, such as heat, light, pressure, and chemicals. Interoreceptors detect stimuli originating inside the body, such as blood pressure and body position. Sensory receptors convey the energy of stimuli into membrane potentials and transmit signals to the nervous system. Sensory receptors perform four functions in this process: sensory transduction, amplification, transmission, and integration. The conversion of stimulus energy into a change in membrane potential of a sensory receptor is sensory transduction. The change in membrane potential itself is receptor potential. Receptor potentials are graded potentials; their magnitude varies with the strength of the stimulus. All receptor potentials result from the opening or closing of ion channels in the sensory receptor’s plasma membrane. Many sensory receptors are extremely sensitive.
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