Chapter 44.docx - Chapter 44 The Sensory System Overview of the sensory system Sensory receptors detect stimulus and motor effectors respond to it

Chapter 44.docx - Chapter 44 The Sensory System Overview of...

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Chapter 44: The Sensory System Overview of the sensory system Sensory receptors detect stimulus and motor effectors respond to it External and Internal stimuli Exteroceptors: sense stimuli that arise in the external environment Interoceptors: sense stimuli that arise from within the body o Muscle tension, limb position, pain, blood chemistry, blood volume, pressure, body temp o Closer to primitive sensory receptors 3 categories Mechanoreceptos: stimulated by mechanical forces such as pressure. o Touch, hearing, balance Chemoreceptors: detect chemicals or chemical changes o Smell and taste Electromagnetic receptors: react to heat and light energy o Photoreceptors of eyes that detect light, thermal receptors Sensory info in 4 steps: From sensory neurons to CNS 1. Stimulation: impinges on a sensory neuron or an associated, but separate sensory receptor 2. Transduction: Stimulus energy is transformed into graded potentials in the dendrites of the sensory neuron 3. Transmission: Action potentials develop into the axon of the sensory neuron and are conducted to the CNS along an afferent nerve pathway. 4. Interpretation: The brain creates a sensory perception from the electrochemical event produced by afferent stimulation a. Perceive with brain not sensory organs Sensory Transduction involves gated ion channels Stimulus gated ion channels in their membranes Sensory stimulus causes these gates to open or close o Most cases, sensory stimulus produces a depolarization of the receptor cell similar to EPSP The depolarization in a sensory receptor on stimulation is referred to as a receptor potential o Graded potential o The larger the sensory stimulus, the greater the degree of depolarization, higher the frequency of action potentials o Decrease in size with distance Logarithmic relationship between sensory intensity and action potential frequency
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o Allows CNS to interpret strength of a sensory stimulus based on the frequency of incoming signals Mechanoreceptors: Touch and Pressure Receptors of skin: cutaneous, interoceptors, respond between external and internal Pain receptors o Nociceptors: sensitive to noxious substances and tissue damage Transmit impulses perceived as pain Consist of free nerve endings especially where the damage is Some respond even before damage has occurred o Many hyper stimulated sensory receptors can produce perception of pain in the brain Transient receptor protein ion channels o Extremes f temp o TRP: stimulated by temp to produce an inward flow of cations, mainly Na+/Ca2+ o This depolarization causes sensory neuron to fire Release of glutamate and EPSP in neurons in the spinal cord Pain response Thermoreceptors detect change in heat energy o Skin contains 2 populations of thermoreceptors Naked dendritic endings of sensory neurons that are sensitive to changes in temp Contain free nerve endings Contain TRP ion channels that are responsive to hot or cold o
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