Slide 1Slide 2Slide 3Neurons are the functional units of the nervous systemSlide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14A nerve signal begins as a change in the membrane potentialSlide 16Slide 17Slide 18The action potential propagates itself along the axonNeurons communicate at synapsesSlide 21Chemical synapses enable complex information to be processedSlide 23A variety of small molecules function as neurotransmittersCONNECTION: Many drugs act at chemical synapsesSlide 26The peripheral nervous system of vertebratesSlide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34The structure of a living supercomputer: The human brainThe structure of a living supercomputer: The human brainThe structure of a living supercomputer: The human brainSlide 38Slide 39Biology 003: Organisms in Their EnvironmentLecture #9 – Nervous SystemNERVOUS SYSTEM STRUCTURE AND FUNCTION© 2012 Pearson Education, Inc.Figure 28.1ASensory receptorMuscle cellsSensory inputMotor outputIntegrationBrain and spinal cordCentral nervoussystem (CNS)Peripheral nervoussystem (PNS)Neurons are the functional units of the nervous systemNeurons are –cells specialized for carrying signals–the functional units of the nervous system.A neuron consists of –a cell body and–two types of extensions (fibers) that conduct signals,–dendrites–axonsFigure 28.2Signal directionNucleusMyelinsheathSchwanncellDendritesCellbodyAxonNodes of RanvierSignalpathwayNode of RanvierSynapticterminalsNucleusSchwanncellCell bodyLayers ofmyelinThe central nervous system (CNS) consists of the–brain–spinal cord (vertebrates).The peripheral nervous system (PNS)–is located outside the CNS–consists of –nerves (bundles of neurons wrapped in connective tissue) and–ganglia (clusters of neuron cell bodies).Nervous systems receive sensory input, interpret it, and send out appropriate commandsSensory neurons–convey signals from sensory receptors to the CNS.Interneurons–are located entirely in the CNS,–integrate information, and–send it to motor neurons.Motor neurons convey signals to muscle cells.The nervous system receives sensory input, interprets it, and sends out appropriate commandsFigure 28.1BSensoryreceptor2134SensoryneuronBrainSpinalcordInterneuronCNSPNSNerveFlexormusclesQuadricepsmusclesGanglionMotorneuronThe knee-jerk reflexNERVE SIGNALS AND THEIR TRANSMISSIONNerve function depends on charge differences across neuron membranesAt rest, a neuron’s plasma membrane has potential energy—the membrane potential, in which–just inside the cell is slightly negative and–just outside the cell is slightly positive.The resting potential is the voltage across the plasma membrane of a resting neuron.Ion – atom with an electric charge due to the loss or gain of electrons (e-)e.g., a sodium atom (Na) that has lost an electron is labeled as Na+The resting potential exists because of differences in ion concentration of the fluids inside and outside the neuron.–Inside the neuron–K+ is high and–Na+ is low.–Outside the neuron–K+ is low and–Na+ is high.Nerve function depends on charge differences across neuron membranesNeuronAxonPlasmamembranePlasmamembraneNachannelOutside of neuronK channelInside of neuronNaNaNaNaNaKKKKKKKKKKKNaNaNaNaNaNaNaNaNaNaNaNaNaNaKKKKKNa-KpumpATPKFigure 28.3_2PlasmamembraneNachannelOutside of neuronK channelInside of neuronNaNaNaNaNaKKKKKKKKKNaNaNaNaNaNaNaNaNaNaNaKKKKNa-KpumpATPKKKNaNaNaK-A nerve signal begins as a change in the membrane potentialA stimulus is any factor that causes a nerve signal to be generated.A nerve signal, called an action potential, is–a change in the membrane voltage:–from the resting potential,–to a maximum level, and–back to the resting potential.Figure 28.4NaNaKAdditional Na channelsopen, K channels areclosed; interior of cellbecomes more positive.NaNa2KA stimulus opens some Nachannels; if threshold is reached,an action potential is triggered.NaNaK1Resting state: Na and K channels are closed; resting potential ismaintained.SodiumchannelPotassiumchannelOutsideof neuronPlasma membraneInside of neuronActionpotentialThresholdResting potentialTime (msec)Membrane potential(mV)500501002313451NaNaK4Na channels closeand inactivate; K channels open, andK rushes out;interior of cell is morenegative than outside.NaNaKThe K channelsclose relativelyslowly, causing abrief undershoot. 51 Return to restingstate.Resting potential is -70mVFigure 28.3_2PlasmamembraneNachannelOutside of neuronK channelInside of neuronNaNaNaNaNaKKKKKKKKKNaNaNaNaNaNaNaNaNaNaNaKKKKNa-KpumpATPKKKNaNaNaK-Resting potential reset via protein pump + ATPFigure 28.5AxonPlasmamembraneAxonsegmentActionpotentialNaNaNaAction potentialNaNaAction potentialKKKKNa123The strength of the stimulus alters the frequency of action potentials.–The strength of the action potential measured in voltage is always the same.The action potential propagates itself along the axonNeurons communicate at synapsesSynapses are junctions where signals are transmitted between–two neurons or–between a neuron and a muscle cell.Figure 28.6Axon ofsendingcellSynapticterminalof sendingcellDendriteof receiving cellSending cellSynapticvesiclesSynapticterminalSynapticcleftVesicle fuseswith plasmamembraneActionpotentialarrivesNeurotransmitteris released intosynaptic cleftNeurotransmitterbinds to receptorNeurotransmittermoleculesNeurotransmitter brokendown and releasedIon channel closesIonsReceptorReceivingcellNeurotransmitterIon channelsIon channel opens564321Signals travel across synapses via neurotransmittersA receiving neuron’s membrane may receive signals–that are both excitatory and inhibitory–from many different sending neurons.The summation of excitation and inhibition determines if a neuron will transmit a nerve signal.Chemical synapses enable complex information to be processedFigure 28.7DendritesMyelinsheathAxonSynaptic terminalsInhibitoryExcitatoryReceivingcell bodySynapticterminalsA variety