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Sensory Systems

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Physiology 1021
John Ciriello

4th week May3011 1035 AM Module 7Sensory SystemsThe body has several sensory systems that allow it to detect external changes rapidlyyTransduction of Environmental Information is how information from the external environment is turned into language the brain understandsaction potentials In order for the brain to know what is happening outside the body environmental stimuli yenergy like light heat touch or sound must first be detected by sensory receptors which then convert the information into action potentials language of the NS Environmental Stimuli In order for the brain to consciously perceive an environmental stimulus that stimulus MUST BE ydetected by a sensory receptor Environmental stimuli come in different formsand require different receptors to detect the ystimulus and then convert it into APsMechanical Stimuli IncludesTouchyPressureyVibrationyPropioception muscle senseySound yThis stimuli will stretch sensory receptors in the skin and open ion channels causing a ydepolarization of the sensory neuron producing an AP Chemical StimuliIncludes TasteyPainyOdours yLike a sour taste on the tongue or an odour in the nose binds with a receptor causing ydepolarization and then an APAn Electromagnetic Stimulus IncludesLightyLight energy is absorbed by PHOTORECEPTORS of the eye rods and cones in the retina and yeventually produces APsOther Stimuli IncludesGravityyMotionyAcceleration y Heaty Gravity and motion can ALSO be detected by hair cells in the vestibular system which convert ythis form of external stimulus to APsAdequate Stimulus for the ReceptorSome receptors can detect more than one type of stimulus yAn ADEQUATE STIMULUS is a particular form of and environmental stimulusto which sensory yreceptor is MOST sensitive The adequate stimulus for rod and cone cells found in the retina of the eye is LIGHT y Sensory receptors DO respond to other forms of energy BUT NOT in the optimal way ex rod and ycone cells can respond to pressure on the eyeballReceptor Generator Potentials0nce the sensory receptor is stimulated by an environmental stimulus it will cause a change in ion ypermeabilityleading to a local depolarization This local depolarization is called a GENERATOR or RECEPTOR POTENTIAL ySince the receptor does NOT have voltagegated ion channels necessary to fire an APthe yreceptor potential MUST spread out to an area on the sensory neuron that DOES contain these channelsThis is usually at the node of Ranvier on the axonthe AP will then be generated and propagated yalong the axon and into the spinal cord In receptors with NO axon hair cells the depolarization has to spread to the synapse to result in ythe release of a neurotransmitterCONTDExamples of shared characterisitics with EPSPs and IPSPs1 They are generally depolarizing but CAN be hyperpolarizing too2 They are caused by an increase in permeability to sodium ions or potassium ions in the case of a hyperpolarizing stimulus 3 They are local and do not propagate down the neuron like an APbut spread lke and EPSP decreasing with time and distance from the stimulus4 They are proportional to the strength of the stimulusthe stronger the stimulus the larger the receptor potential and the more likely to fire an AP The Somatosensory SystemDetects and processes the sensations of touch vibration temperature and painthe majority of ywhich originate in the skin Detecting each sensation requires several different sensory receptors within the skin yThe receptors in the skin are referred to as cutaneous receptors they includey 1 Hair follicle receptorsthat are sensitive to fine touch and virbation
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