Presentation on theme: "Monday April 11, 2014. Nervous system and biological electricity III"— Presentation transcript:
1Monday April 11, 2014.Nervous system and biological electricity III1. No pre-lecture quiz2. A review of Action potentials3. Myelin4. Synapses and neurotransmitters
2The Action Potential Is a Rapid Change in Membrane Potential 1. Depolarizationphase2. RepolarizationphaseThreshold potentialResting potential3. Hyperpolarization phase
3Voltage-gated sodium channels allow the action potential to occur https://www.youtube.com/watch?v=ifD1YG07fB8
4Voltage-gated channels Two important types:1.) Na+ voltage gated channels2.) K+ voltage gated channelsHow voltage-gated channels workAt the resting potential, voltage-gated Na+ channels are closed.Conformational changes openvoltage-gated channels whenthe membrane is depolarized.
5Resting Potential - Both voltage gated Na+ and K+ channels are closed.
6Initial Depolarization - Some Na+ channels open Initial Depolarization - Some Na+ channels open. If enough Na+ channels open, then the threshold is surpassed and an action potential is initiated.
7Na+ channels open quickly. K+ channels are still closed. PNa+ > PK+
8Na+ channels self-inactivate, K+ channels are open. PK+ >> PNa+
10Resting Potential - Both Na+ and K+ channels are closed.
11Before the end of the semester you are going to learn how A. how the nerve cell interprets the information incoming from other neurons at the dendrites & axon hillockB. how the signal is propagated along the axonC. how the signal is transferred via neurotransmitters to the next neuron (or muscle as shown in this graph)In order to understand any of this, we need to understand the nature of biological electricity - which is the point of this lecture. Then, we’re going to discuss B (how the signal is propagated along the axon). Then A. and Then C.
12Action Potentials Propagate because Charge Spreads down the Membrane PROPAGATION OF ACTION POTENTIALAxonNeuron1. Na+ enters axon.2. Charge spreads;membrane“downstream”depolarizes.Depolarization atnext ion channel3. Voltage-gatedchannel opens inresponse todepolarization.
13Why does the membrane potential increase during stage 3 of the action potential? A. Both the voltage-gated Na+ channels and voltage gated K+ channels are open.B. All of the K+ channels (both leak and voltage gated) are open.C. The voltage gated Na+ channels are open, but the voltage gated K+ channels havenot opened yet.D. The voltage gated Na+ channels are open, but the K+ channels (both voltage gated and leak) have not opened yet.
14Why does the membrane potential decrease during stage 4 of the action potential? A. The voltage gated K+ channels open.B. The voltage gated Na+ channels open.C. The voltage gated K+ channels close.D. The voltage gated Na+ channels close.E. A and D
15Action Potentials Propagate Quickly in Myelinated Axons Action potentials jump down axon.Action potential jumpsfrom node to nodeNodes of RanvierAxonSchwann cells (glia)wrap around axon,forming myelin sheathSchwann cell membranewrapped around axon
16The process of coating axons with myelin is incomplete when humans are born. This is part of the reason why babies are uncoordinated and slow learners.Babies need lots of fat – not only for energy storage but also to myelinate their neurons.
17Multiple Sclerosis (MS) Disease results in damage to myelin and impairs electrical signaling.Muscles weaken and coordination decreases.
20ACTION POTENTIAL TRIGGERS RELEASE OF NEUROTRANSMITTER Na+ and K+channelsPresynapticmembrane(axon)Postsynaptic(dendrite orcell body)Actionpotentials1. Action potential arrives;triggers entry of Ca2+.2. In response to Ca2+, synapticvesicles fuse with presynapticmembrane, then releaseneurotransmitter.3. Ion channels open whenneurotransmitter binds; ionflows cause change inpostsynaptic cell potential.4. Ion channels will close asneurotransmitter is brokendown or taken back up bypresynaptic cell (not shown).
22Ion Channels on Post-synaptic Cell at Synapse Some only let Na+ pass through.Some let Na+/K+ pass through.Some only let K+ pass through.Some increase the permeability of Cl-.
23Excitatory vs. Inhibitory Synapses Excitatory synapses cause the post-synaptic cell to become less negative triggering an excitatory post-synaptic potential (EPSP)Increases the likelihood of firing an action potentialInhibitory synapses cause the post-synaptic cell potential to become negative triggering an inhibitory post-synaptic potentialDecreases the likelihood of firing an action potential
24Postsynaptic Potentials Can Depolarize or Hyperpolarize the Postsynaptic Membrane Depolarization,Na+ inflowHyperpolarization, K+outflow or Cl– inflowDepolarization andhyperpolarizationstimuli appliedExcitatorypostsynapticpotential(EPSP)Inhibitorypostsynapticpotential(IPSP)EPSP IPSPResting potential
25Neurons Integrate Information from Many Synapses Most neurons receive information from many other neurons.Axons ofpresynaptic neuronsDendrites ofpostsynaptic neuronCell body ofpostsynaptic neuronAxonhillockAxon of postsynaptic cellExcitatory synapseInhibitory synapse
26Neurons Integrate Information from Many Synapses Postsynaptic potentials sum.Action potentialThresholdRestingpotential
28NeurotransmittersMore than 100 neurotransmitters are now recognized, and more will surely be discovered.Acetylcholine is important and one of the first ones discovered because its involvement in muscle movement.Dopamine and serotonin hugely important for many behaviors.The workhorses of the brain are glutamate, glycine, and γ-aminobutyric acid (GABA).
29Acetylcholine Stimulates muscles Also found throughout nervous system Usually excitatory, but can be inhibitory depending on the receptor
33Serotonin Excitatory or inhibitory depending on area of CNS Ecstasy (MDMA) causes increased releaseInvolved in sleep, appetite, moodDrugs like prozac (SSRIs – selective serotonin reuptake inhibitor) slows down transport proteinTransporter also binds cocaine and amphetamines.
34The Autonomic Nervous System Controls Internal Processes PARASYMPATHETIC NERVES“Rest and digest”SYMPATHETIC NERVES“Fight or flight”Constrict pupilsDilate pupilsStimulate salivaInhibit salivationSlow heartbeatCranialnervesIncrease heartbeatCervicalnervesConstrict airwaysRelax airwaysStimulate activityof stomachInhibit activityof stomachThoracicnervesInhibit release ofglucose; stimulategallbladderStimulate releaseof glucose; inhibitgallbladderStimulate activityof intestinesInhibit activityof intestinesLumbarnervesSecreteepinephrine andnorepinephrine(hormones thatstimulate activity;see Chapter 47)SacralnervesContract bladderSympathetic chain:bundles of nervesthat synapse withnerves from spinalcord, then sendprojections to organsRelax bladderPromote erectionof genitalsPromoteejaculation andvaginal contraction
35The Functions of the PNS Form a Hierarchy Central nervous system (CNS)Information processingPeripheral nervous system (PNS)Sensoryinformationtravels inafferent divisionMost informationtravels inefferent division,which includes…SomaticnervoussystemAutonomicnervous systemSympatheticdivisionParasympatheticdivision