3_Sensory - Sensory systems Based on our understanding of...

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Unformatted text preview: Sensory systems Based on our understanding of neurons and the nervous system, we now ask the question: how are environmental stimuli converted to information in the nervous system? In other words, how do we sense sound, odor, light, and other stimuli? In humans, sensory cells convert (or transduce) physical and chemical stimuli from the environment into signals that are transmitted to other parts of the nervous system. Different types of sensory cells are specialized for detecting different types of stimuli, such as sound (in hearing), odor (in smell), and light (in vision). Sensory cells may be assembled with other types of cells into sensory organs, such as ears, noses and eyes. The sensory organs enhance the ability of the sensory cells to collect and amplify stimuli from the environment. Most sensory cells are modified neurons, but some are other types of cells closely associated with neurons. The plasma membranes of sensory cells contain receptor proteins. When a receptor protein is activated by a specific stimulus, it opens or closes ion channels in the plasma membrane by one of several mechanisms, as illustrated in Figure 45.1. An activated receptor protein maybe part of an ion channel, and may open or close the channel directly by changes in its conformation( or three- dimensional system)-Typical of mechanoreceptors, which respond to changes in pressure. Alternatively, an activated receptor protein may act indirectly by initiating a signal transduction cascade that controls the opening or closing of an associated ion channel in the plasma membrane. -Typical of chemo receptors and photoreceptors, which respond to chemical and light stimuli respectively. In each case, the opening or closing of ion channels by the activated receptor proteins alters the membrane potential of the sensory cell, resulting in a receptor potential . The receptor potential must be converted into an action potential in order for the signal from the sensory cell to be propagated in the nervous system. Some sensory cells are capable of generating action potentials themselves. In such cells, the receptor potential spreads to a region of the plasma membrane that contains voltage-gated sodium channels. Opening of the voltage-gated sodium channels causes an action potential to be generated and propagated by the membrane of the sensory cell. Other sensory cells lack the ability to generate action potentials....
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3_Sensory - Sensory systems Based on our understanding of...

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