BILD 2: Multicellular LifeLECTURE #2[Website: http://www.biology.ucsd.edu/classes/bild2.WI08.2]Instructor: Darwin K. [email protected] 48.5 Structure of a vertebrate neuronDendritesCell bodyNucleusAxon hillockAxonSignal directionSynapseMyelin sheathSynapticterminalsPresynaptic cellPostsynaptic cellFigure 48.6 Structural diversity of vertebrate neuronsAxonCell bodyDendrites(a) Sensory neuron(b) Interneurons(c) Motor neuronFigure 48.20 Ventricles, gray matter, and white matterGray matterWhitematterVentriclesFigure 48.4 The knee-jerk reflex Sensory neurons from the quadriceps also communicatewith interneurons in the spinal cord. The interneurons inhibit motor neurons that supply the hamstring (flexor) muscle. This inhibition prevents the hamstring from contracting, which would resist the action of the quadriceps. The sensory neurons communicate with motor neurons that supply the quadriceps. The motor neurons convey signals to the quadriceps, causing it to contract and jerking the lower leg forward.456The reflex is initiated by tapping the tendon connected to the quadriceps (extensor) muscle.1 Sensors detecta sudden stretch in the quadriceps.2 Sensory neuronsconvey the information to the spinal cord.3QuadricepsmuscleHamstringmuscleSpinal cord(cross section)Gray matterWhite matterCell body of sensory neuronin dorsal root ganglionSensory neuronMotor neuronInterneuronFigure 48.19 The vertebrate nervous systemCentral nervoussystem (CNS)Peripheral nervoussystem (PNS)BrainSpinal cordCranialnervesGangliaoutsideCNSSpinalnervesFigure 48.21 Functional hierarchy of the vertebrate peripheralnervous systemPeripheralnervous systemSomaticnervoussystemAutonomicnervoussystemSympatheticdivisionParasympatheticdivisionEntericdivisionFigure 48.22 The parasympathetic and sympathetic divisionsof the autonomic nervous systemParasympathetic division Sympathetic divisionAction on target organs:Action on target organs:Location ofpreganglionic neurons:brainstem and sacralsegments of spinal cordNeurotransmitterreleased bypreganglionic neurons:acetylcholineLocation ofpostganglionic neurons:in ganglia close to orwithin target organsNeurotransmitterreleased bypostganglionic neurons:acetylcholineConstricts pupilof eyeStimulates salivarygland secretionConstrictsbronchi in lungsSlows heartStimulates activityof stomach andintestinesStimulates activityof pancreasStimulatesgallbladderPromotes emptyingof bladderPromotes erectionof genitaliaCervicalThoracicLumbarSynapseSympatheticgangliaDilates pupilof eyeInhibits salivary gland secretionRelaxes bronchiin lungsAccelerates heartInhibits activity of stomach and intestinesInhibits activityof pancreasStimulates glucoserelease from liver;inhibits gallbladderStimulatesadrenal medullaInhibits emptyingof bladderPromotes ejaculation and vaginal contractionsSacralLocation ofpreganglionic neurons:thoracic and lumbarsegments of spinal cordNeurotransmitterreleased bypreganglionic neurons:acetylcholineLocation ofpostganglionic neurons:some in ganglia close totarget organs; others ina chain of ganglia near spinal cordNeurotransmitterreleased bypostganglionic neurons:norepinephrineFigure 48.9 Intracellular RecordingAPPLICATION Electrophysiologists use intracellular recording to measure the membrane potential of neurons and other cells.TECHNIQUE A microelectrode is made from a glass capillary tube filled with an electrically conductive salt solution. One end of the tube tapers to an extremely fine tip (diameter < 1 µm). While looking through a microscope, the experimenter uses a micropositioner to insert the tip of the microelectrode into a cell. A voltage recorder (usually an oscilloscope or a computer-based system) measures the voltage between the microelectrode tip inside the cell and a reference electrode placed in the solution outside the cell.MicroelectrodeReferenceelectrodeVoltage recorder–70 mVFigure 48.10 Ionic gradients across the plasma membrane of amammalian neuronCYTOSOLEXTRACELLULARFLUID[Na+]15 mM[K+]150 mM[Cl–]10 mM[A–]100 mM[Na+]150 mM[K+]5 mM[Cl–]120 mM–––––+++++PlasmamembraneFigure 48.11 Modeling a mammalian neuronInner chamberOuter chamberInner chamberOuter chamber–92 mV +62 mVArtificialmembranePotassiumchannelK+Cl–150 mMKCL150 mMNaCl15 mMNaCl5 mMKCLCl–Na+Sodium channel+ –+ –+ –+ –+ –+ –(a) Membrane selectively permeable to K+(b) Membrane selectively permeable to Na+Figure 48.12 Graded potentials and an action potential in aneuron+500–50–100+500–50–100+500–50–100Time (msec)Time (msec)Time (msec)0 1 2 3 4 50 1 2 3 4 50 1 2 3 4 5 6ThresholdThresholdThresholdRestingpotentialRestingpotentialRestingpotentialHyperpolarizationsDepolarizationsMembrane potential (mV)Membrane potential (mV)Membrane potential (mV)StimuliStimuliStronger depolarizing stimulusActionpotential(a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K+. The larger stimulus producesa larger hyperpolarization.(b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na+.The larger stimulus produces alarger depolarization.(c) Action potential triggered by a depolarization that reaches the
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