Chapter 44 Outline.docx - Chapter 44 Sensory Systems 44.1 Overview of Sensory Receptors Vision hearing taste smell and touch o Provide information about

Chapter 44 Outline.docx - Chapter 44 Sensory Systems 44.1...

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Chapter 44: Sensory Systems 44.1 Overview of Sensory Receptors Vision, hearing, taste, smell, and touch o Provide information about our environment Sensory receptors can also provide information about our internal states o Stretching of muscles, position of body, blood pressure Sensory receptors detect both external and internal stimuli o Exteroceptors sense stimuli that arise in external environment Evolved in water before land Some stimuli travel better in water Mammalian hearing converts airborne stimulus into a water one o Interoceptors sense stimuli that arise from within the body Muscle length and tension, limb position, pain, blood chemistry, blood volume and pressure, and body temperature Simpler Closer resemblance to primitive sensory receptors Receptors can be grouped into three categories o Mechanoreceptors stimulated by mechanical forces Touch, hearing, and balance o Chemoreceptors detect chemicals or chemical changes Smell and taste o Electromagnetic receptors react to heat and light energy Photoreceptors of eyes Thermal receptors in some reptiles o Simplest sensory receptors are free nerve endings React to bending or stretching of the sensory neuron’s membrane in response to changes in temperature or to chemicals Sensory information is conveyed in a four step process 1. Stimulation physical stimulus impinges on a sensory neuron or an associated, but separate, sensory receptor 2. Transduction stimulus energy is transformed into graded potentials in dendrites of sensory neuron 3. Transmission action potentials develop in axon of sensory neuron and are then conducted to CNS along afferent pathway 4. Interpretation brain creates sensory perception from the electrochemical events produced by afferent stimulation (we actually perceive five senses with our brain, not sensory organs) Sensory transduction involves gated ion channels o Sensory cells respond to stimuli because they have stimulus- gated ion channels 1
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Sensory stimulus causes these ion channels to open or close Usually they open resulting in depolarization of the cell (EPSP) Referred to as a receptor potential o Receptor potential is a graded potential Larger the sensory stimulus, the greater the degree of depolarization Also decrease in size with distance from their source If depolarization is great enough, AP propagates along the sensory axon into the CNS o Greater the sensory stimulus, greater the depolarization, and higher the frequency of action potentials Frequency conveys intensity of stimulus Logarithmic relationship Sensory stimulus that is 10 times greater will produce action potentials at twice the frequency o This relationship allows CNS to interpret the strength of a sensory stimulus 44.2 Mechanoreceptors: Touch and Pressure Cutaneous receptors classified as interoceptors o Respond to stimuli at border between external and internal environments o
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  • Spring '08
  • DR.ILYASAPOZHNIKOV
  • Biology, RNA, Photoreceptor cell, sensory receptor

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