Lecture_Notes_Chapter_50 - Chapter 49 Sensory Mechanisms...

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Chapter 49: Sensory Mechanisms Sensory organs mediate the responses of animals to changes in the environment Avoidance of unfavorable conditions, enemies Attraction to food sources, mates Sensory receptors receive stimuli in the form of energy of a particular physical quality and transduce them into a signal that can be transmitted and integrated in the nervous system Light Heat Sound Touch Gravity pressure Magnetism o Electric fields Chemical qualities = smell, taste, oxygen, CO 2 Most stimuli represent forms of energy – the biological process of sensation involves converting this energy into a change in the membrane potential of sensory receptors Not all forms of energy are perceived by animals Large parts of the electromagnetic radiation spectrum Radioactivity o No relevance or adaptive value in perceiving these Another characteristic of sensory perception is the sensitivity of the cells and organs involved The energy received by the sensory system has no relation to the energy output Single photons, single odor molecules can be perceived by some animals! o Implies amplification of the signal! Functions Performed by Sensory Receptors Sensory transduction Amplification Transmission Integration Two types of sensory receptors exhibit these functions: Exteroreceptors o Detect stimuli coming from the outside of the body Interoreceptors o Detect internal stimuli Sensory Transduction
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Sensory transduction is the conversion of stimulus energy into a change in the membrane potential of a sensory receptor This change in the membrane potential is known as a receptor potential Amplification Amplification is the strengthening of stimulus energy by cells in sensory pathways Transmission After energy in a stimulus has been transduced into a receptor potential some sensory cells generate action potentials, which are transmitted to the CNS Sensory cells without axons release neurotransmitters at synapses with sensory neurons Integration The integration of sensory information begins as soon as the information is received and occurs at all levels of the nervous system Receptor potentials are integrated through summation sensory adaptation o A decrease in responsiveness during continued stimulation Types of Sensory Receptors Based on the energy they transduce, sensory receptors fall into five categories Mechanoreceptors Chemoreceptors Electromagnetic receptors Thermoreceptors Pain receptors Mechanoreceptors Mechanoreceptors sense physical deformation caused by stimuli such as pressure, stretch, motion, and sound The mammalian sense of touch relies on mechanoreceptors that are the dendrites of sensory neurons Chemoreceptors General receptors that transmit information about the total solute concentration of a solution Specific receptors that respond to individual kinds of molecules o Two of the most sensitive and specific chemoreceptors known are present in the antennae
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Lecture_Notes_Chapter_50 - Chapter 49 Sensory Mechanisms...

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