1 chapter 15: neural integration i: sensory pathways and the somatic nervous system

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  • Chapter 15:

    Neural Integration I: Sensory Pathways and the Somatic Nervous System

  • Neural Integration

  • Afferent Division of the Nervous SystemReceptorsSensory neuronsSensory pathways

  • Afferent DivisionSensory receptors sensory pathway Somatic Sensory infoSensory cortex of cerebrumCerebellumVisceral Sensory infoReflex centers in brainstemReflex centers in diencephalon

  • Sensory ReceptorsSpecialized 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

  • Sensory ReceptorsSensation the sense info; action potentialsTaste, hearing, equilibrium, and vision provided by specialized receptor cellsCommunicate with sensory neurons across chemical synapsesPerception conscious awareness of sensation

  • Sensory ReceptorsTransduction conversion of environmental stimulus into action potential by sensory receptorAction potential:When stimulated, a receptor passes information to the CNS in the form of action potentials along the axon of a sensory neuronReceptors specific for particular type of stimulusSpecificity is due to structure of receptorSimplest receptors are dendrites (free nerve endings), least specific

  • Free Nerve EndingsBranching tips of dendrites Not protected by accessory structures Can be stimulated by many different stimuli

  • Sensory ReceptorsReceptive field area monitored by single receptor (e.g. touch: arm vs. fingertip)Area is monitored by a single receptor cellThe larger the receptive field, the more difficult it is to localize a stimulus

  • Sensory ReceptorsLabeled lineLink between receptor and processing site in CNSStimulation anywhere on labeled line will produce the same perception (e.g. phantom limb)Stimulus -> receptor -> transduction -> action potential -> sensation ->-> CNS perception

  • Sensory PathwaysDeliver somatic and visceral sensory information to their final destinations inside the CNS using:nervesnucleitracts

  • Sensory ReceptorsTonic Receptors:Always activeSignal at different rate when stimulatedMonitor background levelsPhasic Receptors:Activated by stimulusBecome active for a short time whenever a change occursMonitor intensity and rate of change of stimulus

  • Sensory ReceptorsAdaptation Reduced sensitivity to a constant stimulusPeripheral Adaptation:Reduction in receptor activityPhasic fast adaptingTonic slow or non adaptingRemind you of an injury long after the initial damage has occurredCentral Adaptation:Inhibition of nuclei along labeled lineNot all pathways will adapt

  • Four 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

  • 1. Pain Receptors: NociceptorsDetect PainAre common in the:superficial portions of the skinjoint capsuleswithin the periosteum of bonesaround the walls of blood vesselsRare in deep tissue and visceral organsConsist of free nerve endings with large receptor fieldsFigure 152

  • 1. Pain Receptors: NociceptorsMode 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-oxygenase

  • 1. Pain Receptors: NociceptorsOnce transduced pain sensations are carried on either type A and type C fibers/axons:Type A:Fast pain; stab or cut; triggers defensive reflexes Type C:Slow pain; aching painTonic receptors with no peripheral adaptationPain levels are modulated by endorphins which inhibit CNS function

  • 2. ThermoreceptorsDetect temperatureFound in skin, skeletal muscle, liver, and hypothalamusConsist of free nerve endingsPhasic receptors that adapt easily

  • 3. Mechanoreceptors**Detect membrane distortion Three receptor types:Tactile ReceptorsProprioceptorsBaroreceptors

  • 3. MechanoreceptorsTactile ReceptorsDetect touch, pressure and vibration on skinFree nerve endingsDetect touch on skinTonic receptors with small receptor fieldsRoot hair plexus nerve endingsDetect hair movementPhasic receptors, adapt rapidlyTactile discs/Merkels discsDetect fine touch Extremely sensitiveWhole cell tonic receptors

  • 3. MechanoreceptorsTactile ReceptorsTactile corpuscles/Meissners corpusclesDetect fine touch and vibrationLarger receptor structurePhasic receptors, adapt rapidlyLamellated corpuscles/Pacinian corpusclesDetect deep pressureLarger multi-layer receptorsPhasic receptor, adapt rapidlyRuffini corpusclesDetect pressure and distortionLarge tonic receptors, no adaptation

  • 3. MechanoreceptorsProprioceptors:Detect positions of joints and musclesTonic receptors, do not adapt, complexMuscle 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 joint

  • 3. MechanoreceptorsBaroreceptorsDetect pressure changesFound in elastic tissue of blood vessels and organs of digestive, reproductive and urinary tractsConsists of free nerve endingsPhasic receptors, adapt rapidly

  • 4. ChemoreceptorsDetect change in concentration of specific chemicals or compoundsE.g. pH, CO2Found in respiratory centers of the brain and in large arteriesPhasic receptors, adapt rapidly

  • KEY CONCEPTStimulation of a receptor produces action potentials along the axon of a sensory neuron The frequency and pattern of action potentials contains information about the strength, duration, and variation of the stimulus Your perception of the nature of that stimulus depends on the path it takes inside the CNS

  • Somatic Sensory Pathways Carry sensory information from the skin and musculature of the body wall, head, neck, and limbs

  • Somatic Sensory PathwaysConsist of two or three neurons:First Order Neuron:Sensory neuronConnects from receptor to CNSCell body is in dorsal root ganglion/cranial nerve ganglionSecond Order Neuron:Interneuron (stimulated by first order)Located in spinal cord or brain stemSubconscious processing of infoThird Order Neuron:Located in thalamusRelays info to primary somatosensory cortex of cerebrum for conscious awareness (perception)

  • Only ~1% of somatic sensory info reaches cerebrum (major changes only, background in filtered)LSD interferes with sensory damping/filtering = sensory overloadAll sensory info undergoes decussation in spine before reaching target in CNS

  • 3 Major Somatic Sensory PathwaysFigure 154

  • Posterior Column PathwayCarries sensations of highly localized (fine) touch, pressure, vibration, and proprioceptionFigure 155a

  • Visceral Sensory PathwaysInteroceptors transmit info to solitary nucleus of medulla oblongata for relay to visceral centers in brainstem and diencephalonNo perceptionTwo neurons: 1st and 2nd order

  • Efferent DivisionConscious and subconscious motor centers in brain -> motor pathways ->Somatic Nervous System skeletal muscleAutonomic Nervous System visceral effectors - Smooth and cardiac muscle, glands, and adipose

  • Somatic Nervous SystemMotor control of skeletal muscleConsists of two neurons:Upper motor neuronHas soma in CNS processing center:Primary motor cortex of cerebrum - voluntary controlCerebrum, diencephalon, and brain stem-subconscious control:reflexBasal nuclei of cerebrum and cerebellum-coordination, balance, fine tuningLower motor neuronSoma in brain stem or spinal cordLinks to skeletal muscle motor unit

  • Motor Homunculus

  • Sensory HomunculusFunctional map of the primary sensory cortex

    Figure 155a, b

  • Processing in the Thalamus Determines whether you perceive a given sensation as fine touch, as pressure, or as vibration

  • Motor Related DisorderParkinsons DiseaseJittery movements: lack of fine tuning of motorResults from degeneration of dopamine neurons of substantia nigra Inhibits basal nucleiOveractive basal nuclei = ticksAmylotrophic Lateral SclerosisDegeneration of motor neurons in CNSCauses muscle atrophy and death

  • Motor Related Disorder3. Epilepsy1/25 peopleWide range in condition:Absence seizures (blank) to grand mal seizures (convulsions, unconscious)Uncontrolled/chaotic neuron activity in brain: blocks normal messages

  • When the nociceptors in your hand are stimulated, what sensation do you perceive?painheatvibrationpressure

  • What would happen to you if the information from proprioceptors in your legs were blocked from reaching the CNS?no pain sensations from the legsuncontrolled blood pressure in the legsuncoordinated movements and inability to walkno tactile sensations in the legs

  • Chapter 16:

    Neural Integration II: The Autonomic Nervous System and Higher-Order Functions

  • Autonomic Nervous System (ANS)Operates without conscious instructionCoordinates systems functions:cardiovascularrespiratorydigestiveurinaryreproductive

  • Autonomic Nervous SystemMotor control of visceral effectorsInvolves three neurons:Visceral motor nuclei in hypothalamus to autonomic nuclei in CNSAutonomic nuclei to autonomic ganglia in PNSAuton


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