Lever SystemCannot have both high mechanical advantage and velocity ratioHigh Mechanical advantageIncrease speed by increased muscle lengthHigh Velocity RatioIncrease force production by increased Cross-sectional areaME = KE + PENervous SystemControl SystemHomeostatic LoopStimulusSensory StructureComparator with Preset reference valueError SignalEffector OrganClosed loop (output affects input)Negative Feedback (Output offsets or negates input)Central Nervous System vs. Peripheral Nervous System(Think A comes before E)Membrane Potential (Vm)Difference in electrochemical gradient inside and outside of cell.Sodium in, Potassium outUse Nernst Equation to approximate VmE Ion = R T ln [Ion]1z F [Ion]2R = gas constant = 1.987 cal/mol-degT = degrees Kz = ion valenceF = Faraday’s Constant 23,062 cal/V-mol@ 37 degrees, RT/F=61.5 (mammals)@ 20 degrees, RT/F = 58Use V=IR and I=VG, where G is conductance to determine voltageDG¢ = RTln [Xi]/[Xo] + zFVm(set DG¢ equal to 0 and solve for Vm)Goldman Equation (takes into account permeabilities)Vm = RT ln (PK)[Ko] + (PNa)[Nao] + (PCl)[Cli]F (PK)[Ki] + (PNa)[Nai] + (PCl)[Clo]The Action Potential1: stimulus arrives at dendritesinduces EPSPs or IPSPssummation of EPSPs à depolarization2: Opening of voltage-gated Na+ channelspositive feedback looprapid depolarizationrising phase of AP3: Na+ channel inactivation, K+ channel activationvoltage-gated Na+ start to close (end of rising phase)voltage-gated K+ channels start to open (peak to trough)4: after-hyperpolarizationtome course of K+ channels causes undershootclosingdrift back to resting Vm5: chemical synapsesopening of voltage-gated Ca++ channelsrelease of neurotransmitter from vesiclesChannel inactivation often occurs after it is opened due to Voltage Difference across membrane (Vm)Sodium ChannelPossesses an inactivation gate@ Resting Membrane potential gate is closed@ Depolarization, gate is opened@ Repolarization, gate is inactivatedNeuronsUnmyelinatedMyelinatedMembrane of a Schwan cell in vertebrate peripheral nervous systemRelatively solid membraneFew membrane proteins or ion channelsInsulator to prevent current leakBare membrane between sections of myelin - Nodes of RanvierIncreases conduction velocityNodes of Ranvier possess a lot of Sodium Channels so the charge jumps hereSynaptic TransmissionAP frequency determinesAmount of Ca++ entering neuron terminal which determinesAmount of neurotransmitter released which determinesMagnitude of post synaptic responseEPSPEPSP --> Depolarization Threshold --> Action Potential --> Excitation Of Post Synaptic StructureIPSPIPSP Hyperpolarization InhibitionInformation carried by a nerve is proportional to the frequency of action potentialsSignal Molecule ReceptorsTrans-membrane proteinSpecificityAlso binds exogenous agonists & antagonistsTransducer – converts signal molecule binding to intracellular responseHistamine ReceptorsHistamine released to initiate inflamatory or allergic response!Take chlorpheneramine, a histaminergic antagonistAxonal AgentsTetrodoxin (TTX) prevents opening of Na channelsSaxitoxin (STX) blocks Na channelsIberiotoxin is scorpion toxin blocking K channels14/12/2012 09:35:00← Lever System- Cannot have both high mechanical advantage and velocity ratio- High Mechanical advantage o Increase speed by increased muscle length- High Velocity Ratioo Increase force production by increased Cross-sectional area←← ME = KE + PE←← Nervous System- Control Systemo Homeostatic Loop Stimulus Sensory Structure Comparator with Preset reference value Error Signal Effector Organo Closed loop (output affects input) Negative Feedback (Output offsets or negates input)←← Central Nervous System vs. Peripheral Nervous System- (Think A comes before E)-CNSPNSSENSORY - AFFERENTMOTOR - EFFERENTINTER-NEURONEFFECTOR GANGLION←← Membrane Potential (Vm)- Difference in electrochemical gradient inside and outside of cell.- Sodium in, Potassium outUse Nernst Equation to approximate Vm- E Ion = R T ln [Ion]1- z F [Ion]2- R = gas constant = 1.987 cal/mol-deg- T = degrees K- z = ion valence- F = Faraday’s Constant 23,062 cal/V-mol←← @ 37 degrees, RT/F=61.5 (mammals)← @ 20 degrees, RT/F = 58 ←← Use V=IR and I=VG, where G is conductance to determine voltage←← DG¢ = RTln [Xi]/[Xo] + zFVm← (set DG¢ equal to 0 and solve for Vm)←← Goldman Equation (takes into account permeabilities)- Vm = RT ln (PK)[Ko] + (PNa)[Nao] + (PCl)[Cli]- F (PK)[Ki] + (PNa)[Nai] + (PCl)[Clo]The Action Potential- 1: stimulus arrives at dendriteso induces EPSPs or IPSPso summation of EPSPs à depolarization- 2: Opening of voltage-gated Na+ channelso positive feedback loopo rapid depolarizationo rising phase of AP- 3: Na+ channel inactivation, K+ channel activationo voltage-gated Na+ start to close (end of rising phase)o voltage-gated K+ channels start to open (peak to trough)- 4: after-hyperpolarizationo tome course of K+ channels causes undershooto closingo drift back to resting Vm- 5: chemical synapseso opening of voltage-gated Ca++ channelso release of neurotransmitter from vesiclesChannel inactivation often occurs after it is opened due to Voltage Difference across membrane (Vm)Sodium Channel- Possesses an inactivation gate- @ Resting Membrane potential gate is closed- @ Depolarization, gate is opened- @ Repolarization, gate is inactivated←← Neurons- Unmyelinated- Myelinatedo Membrane of a Schwan cell in vertebrate peripheral nervous systemo Relatively solid membraneo Few membrane proteins or ion channelso Insulator to prevent current leako Bare membrane between sections of myelin - Nodes of Ranviero Increases conduction velocity← Nodes of Ranvier possess a lot of Sodium Channels so the charge jumps here←← Synaptic Transmission- AP frequency determines- Amount of Ca++ entering neuron terminal which determines- Amount of neurotransmitter released which determines- Magnitude of post synaptic response←← EPSP- EPSP --> Depolarization à Threshold --> Action Potential --> Excitation Of Post Synaptic Structure←← IPSP- IPSP à Hyperpolarization à Inhibition←← Information carried by a nerve is proportional to the frequency of action potentials←← Signal Molecule Receptors- Trans-membrane protein- Specificity- Also binds exogenous agonists & antagonists- Transducer – converts signal molecule binding to intracellular response←← Histamine Receptors- Histamine released to initiate inflamatory
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