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Neural Integration The sensory pathways Chapter 15. Afferent Division of the Nervous System. Receptors Sensory neurons Sensory pathways. Afferent Division – location in CNS. Somatic Sensory info Sensory cortex of cerebrum Cerebellum Visceral Sensory info Reflex centers in brainstem - PowerPoint PPT Presentation

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Neural IntegrationThe sensory pathwaysChapter 15

2Afferent Division of the Nervous SystemReceptorsSensory neuronsSensory pathways3Afferent Division location in CNSSomatic Sensory infoSensory cortex of cerebrumCerebellumVisceral Sensory infoReflex centers in brainstemReflex centers in diencephalon4The somatic sensory systemSensory stimuli that reach the conscious level of perceptionSpecialized cells that monitor specific conditions in the body or external environmentGeneral Senses:Temp, pain, touch, pressure, vibration, proprioceptionSimple receptors located anywhere on bodySpecial Senses: Are located in sense organs such as the eye or earOlfaction, vision, gustation, hearing, equilibriumComplex receptors located in specialized sense organs

Table 10-1 (1 of 2)

General Properties: Sensory Division5From Sensation to Perception

Sensory Pathways from sensation to perceptionStimulus as physical energy sensory receptorReceptor acts as a transducerIntracellular signal usually change in membrane potentialStimulus threshold action potential to CNSIntegration in CNS cerebral cortex or acted on subconsciously78Sensory ReceptorsTransduction conversion of environmental stimulus into action potential by sensory receptorReceptors specific for particular type of stimulusSpecificity is due to structure of receptor

From Sensation to PerceptionA stimulus is a change in the environment that is detected by a receptor Sensation: the awareness of changes in the internal and external environmentPerception: the conscious interpretation of those stimuliClassification by LocationExteroceptorsRespond to stimuli arising outside the bodyReceptors in the skin for touch, pressure, pain, and temperatureMost special sense organsInteroceptors (visceroceptors)Respond to stimuli arising in internal viscera and blood vesselsSensitive to chemical changes, tissue stretch, and temperature changesClassification by LocationProprioceptorsRespond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and musclesInform the brain of ones movements12Four types of General Sensory ReceptorsPain: nociceptorTemperature: thermoreceptorPhysical: mechanoreceptorChemicals: chemoreceptorsAll can be found in both somatic (exteroceptors) and visceral (interoceptors) locations except:Proprioceptors (a mechanoreceptor) are somatic only report the positions of skeletal muscles and joints

13Pain Receptors: Nociceptors(noci = harm) sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals)Free nerve endingMode of Action:Injured cells release arachidonic acidArachidonic acid is converted into prostaglandins by the interstitial enzyme cyclo-oxygenaseProstaglandins activate nociceptorsMany pain medications like aspirin function to inhibit cyclo-oxygenasePain levels are modulated by endorphins which inhibit CNS function

14ThermoreceptorsDetect temperatureFound in skin, skeletal muscle, liver, and hypothalamusConsist of free nerve endingsPhasic receptors that adapt easilyCold response are more superficial and receptors that respond to heat deeperTemperature out of the range of the thermoreceptors will activate nociceptors15MechanoreceptorsDetect membrane distortion Three receptor types:Tactile ReceptorsProprioceptorsBaroreceptors16Mechanoreceptors - Tactile ReceptorsDetect touch, pressure and vibration on skinDetect hair movementDetect fine touchDetect deep pressurerespond to itch (respond among other to histamine) and light touch (detect changes in shape like bending)

Receptor typeStructureLocationFunctionMeissners corpuscle/tactile corpuscleFew spiral terminals surrounded by CT capsuleBetween dermal papillae in hairless skinTouch, pressurePacinian corpuscle/lamellated corpuscleSingle dendrite surrounded by capsule with up to 60 layers of collagen fibersSkin, interosseous membrane, visceraDeep pressure. Respond only when the pressure is first applied (on/off pressure stimulation)Ruffinis corpuscleReceptor endings enclosed by flatten capsuleAll skin, joint capsuleStretching of skin continuous pressure18Mechanoreceptors - ProprioceptorsDetect positions of joints and musclesMuscle spindlesModified skeletal muscle cellMonitor skeletal muscle lengthGolgi tendon organsDendrites around collagen fibers at the muscle-tendon junctionMonitor skeletal muscle tensionJoint capsule receptors-Monitor pressure, tension and movement in the jointReceptor typeStructureLocationFunctionMuscle spindlesSpindle-shape proprioceptors. Modified skeletal muscle fibers enclosed in CT capsulePerimysium of skeletal muscles Detect muscle stretch and initiate reflex that resist stretchGolgi tendon organsProprioceptors. Consist of bundle of collagen fibers enclosed in CT capsule with sensory endings coiling between and around the fibersIn tendons close to skeletal muscle insertionWhen tendon fibers are stretched by muscle contraction the nerve endings are activated by compression. When activated, the contraction of the muscle is inhibited which causes relaxationJoint receptorsProprioceptors (combination of several receptors types Pacinian, Raffini, free ending and Golgi tendon)Joints CT capsuleMonitor stretch in in the articular capsule and provide information on the position and motion of the joint (conscious)20Mechanoreceptors - BaroreceptorsDetect pressure changesFound in elastic tissue of blood vessels and organs of digestive, reproductive and urinary tracts21

22ChemoreceptorsDetect change in concentration of specific chemicals or compoundspH, CO2, sodium etc.Found in respiratory centers of the brain and in large arteriesTable 10-2

Sensory Receptors23Processing of the sensory informationLevels of neural integration in sensory systems:Receptor level the sensor receptorsCircuit level ascending pathways in the CNSPerceptual level neuronal circuits in the cerebral cortex

Figure 13.2

123 Receptor level(sensory receptionand transmissionto CNS) Circuit level(processing inascending pathways) SpinalcordCerebellumReticularformationPonsMusclespindleJointkinestheticreceptorFree nerveendings (pain,cold, warmth) Medulla Perceptual level (processing incortical sensory centers)MotorcortexSomatosensorycortexThalamusProcessing at the Receptor LevelProcessing at the Receptor LevelThe receptor must have specificity for the stimulus energy (as previously discussed) The receptors receptive field must be stimulatedThe stimulus need to be converted to a nerve impulseReceptors have different levels of adaptationInformation is encoded in the frequency of the stimuli the greater the frequency, the stronger is the stimulus.The stimulation of the receptive field affects the discharge of the sensory neuronsThe receptive field is the a specific physical area that, when stimulated, affect the discharge of the stimulus.Most receptive fields activation will result in message sending excitatory receptive fieldSensory receptors in the CNS can have inhibitory receptive field (example: vision fields to determine borders).Sensory neurons of neighboring receptive field may exhibitConvergence many sub-threshold stimuli to sum in the postsynaptic neuronOverlapping with another receptors receptive field sending 2 sensations from the same area (pressure and pain)The smaller the receptive field the greater the ability of the brain to localize the siteFigure 10-3a

One signal goes to the brain.Compass with pointsseparated by 20 mmPrimarysensoryneuronsSkin surfaceSecondarysensoryneurons(a)Sensory Neurons: Two-Point Discriminationconvergence Two-point discrimination28

Two signals go to the brain.Compass with pointsseparated by 20 mmPrimarysensoryneuronsSkin surfaceSecondarysensoryneurons(b)Figure 10-3bSensory Neurons: Two-Point Discrimination - overlapping29Figure 10-2

The receptive fields of three primary sensory neuronsoverlap to form one large secondary receptive field.Primary sensoryneuronsSecondarysensoryneuronSECTION THROUGH SPINAL CORDInformation from thesecondary receptivefield goes to the brain.The primary sensory neuronsconverge on one secondarysensory neuron.Receptive Fields of Sensory Neurons - overlapping30Properties of Stimulus: LocationLateral inhibition enhances contrast and makes a stimulus easier to perceiveFigure 10-6

StimulusStimulusPrimary neuronresponse is proportionalto stimulus strength.Pathway closest tothe stimulus inhibitsneighbors.Inhibition of lateralneurons enhancesperception of stimulus.Tonic levelABCABCTonic levelSkinPinPrimarysensoryneuronsSecondaryneuronsTertiaryneuronsABCFrequency of action potentialsFrequency of action potentials31Transduction allows sensory receptors to respond to stimuli converting sensation into a nerve impulseSensory transduction the process that enables a sensory receptor to respond to a stimulus.The sensory transduction induces a receptor potential in the peripheral terminal of the sensory neuronA receptor potential is a depolarization event that if brings the membrane to a threshold, will become a nerve impulse (AP)The conversion from receptor potential to AP happens in the trigger zone that can be in the first node of Ranvier.In some cases, the peripheral terminal is a separate sensory cell (ex. Photo receptors). In this case there is an involvement of a synapse and NTReceptors adaptationThe duration of a stimulus is coded by duration of action potentials.A longer stimulus generates longer series of APs.If a stimulus persists, some receptors adapt or stop respondingThere are 2 classes of receptors according to how they adapt:Tonic receptors slowly adapting they fire rapidly when first activated, than they slow and maintain firing as long as the stimulus is present (baroreceptors, proprioceptors)Phasic receptors rapidly adapting receptors rapidly firing when first activated but stop firing if the strength of sti

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