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...
Chapter 44: Sensory Systems 44.1 Overview of Sensory Receptors Vision, hearing, taste, smell, and touchoProvide information about our environment Sensory receptors can also provide information about our internal statesoStretching of muscles, position of body, blood pressure Sensory receptors detect both external and internal stimulioExteroceptors sense stimuli that arise in external environment Evolved in water before landSome stimuli travel better in waterMammalian hearing converts airborne stimulus into awater one oInteroceptors sense stimuli that arise from within the body Muscle length and tension, limb position, pain, blood chemistry, blood volume and pressure, and body temperature SimplerCloser resemblance to primitive sensory receptors Receptors can be grouped into three categories oMechanoreceptors stimulated by mechanical forcesTouch, hearing, and balanceoChemoreceptors detect chemicals or chemical changesSmell and tasteoElectromagnetic receptors react to heat and light energyPhotoreceptors of eyesThermal receptors in some reptiles oSimplest sensory receptors are free nerve endingsReact 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 process1. Stimulation physical stimulus impinges on a sensory neuron oran associated, but separate, sensory receptor2. Transduction stimulus energy is transformed into graded potentials in dendrites of sensory neuron3. Transmission action potentials develop in axon of sensory neuron and are then conducted to CNS along afferent pathway4. 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 oSensory cells respond to stimuli because they have stimulus-gated ion channels1
Sensory stimulus causes these ion channels to open or closeUsually they open resulting in depolarization of the cell (EPSP)Referred to as a receptor potential oReceptor potential is a graded potential Larger the sensory stimulus, the greater the degree of depolarizationAlso decrease in size with distance from their sourceIf depolarization is great enough, AP propagates along the sensory axon into the CNSoGreater the sensory stimulus, greater the depolarization, and higher the frequency of action potentialsFrequency conveys intensity of stimulus Logarithmic relationshipSensory stimulus that is 10 times greater will produce action potentials at twice the frequencyoThis relationship allows CNS to interpret the strength of a sensory stimulus 44.2 Mechanoreceptors: Touch and PressureCutaneous receptors classified as interoceptorsoRespond to stimuli at border between external and internal environments o