8 senses 118 - Biology 118 8. SENSORY PHYSIOLOGY An animal...

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Biology 118 8. SENSORY PHYSIOLOGY An animal must be able to receive and interpret information correctly if it is to survive, and the nervous system serves as translator of external stimuli to this end. ENERGY TRANSLATED: Information from the external environment can take various, specific forms – light, mechanical force, chemicals, etc. These stimuli must be translated, or transduced, into action potentials (the only language spoken by neurons). Specific receptor cells are sensitive to particular types of stimuli. Some are actual neurons which send action potentials directly to the nervous system. Other receptor cells can sense a stimulus and then communicate with associated sensory neurons, which then send action potentials to the nervous system. How to differentiate one type of stimulus from another? Sensory modality is achieved by sending action potentials to particular regions of the brain. How to differentiate between a weak and strong stimulus? Stimulus intensity is reflected by the frequency of action potentials fired by sensory neurons. MECHANORECEPTORS : So-called free nerve endings bear stretch-sensitive ion channels on their membranes. When the cell’s membrane is deformed or stretched by mechanical force, these ion channels open, causing changes in membrane voltage. There are several types present in the skin, to detect touch. Baroreceptors are specialized to detect pressure, as they are found in the walls of some blood vessels, the
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8 senses 118 - Biology 118 8. SENSORY PHYSIOLOGY An animal...

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