Lecture4 transmission
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Lecture4 transmission

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    Lecture4 transmission Lecture4 transmission Presentation Transcript

    • Neurons – Electrochemical Communication
    • Preview of today’s lecture Electrochemical Communications  communication between neurons  Neurotransmitters  movie
    • Structure of a synapse presynaptic membrane postsynaptic membrane synaptic cleft
    • Structure of a synapse synaptic vesicles are produced by Golgi apparatus in the soma ORby recycled matter in the cisternae of the terminal button: Pinocytosis
    • Neurons – from electrical to chemical• vesicles release neurotransmitters acrossthe synaptic cleft• the released neurotransmitter leads to post-synaptic potentials (hyperpolarization ordepolarization) that alter the firing rate of thereceiving neuron (decrease or increase) • axon terminal contains synaptic vesicles
    • Structure of the synapse• as viewed under an electron microscope
    • Structure of the synapse• synaptic vesicles fusing with the presynaptic membrane
    • Structure of the synapse• synaptic vesicles fusing with the presynaptic membrane
    • Neurochemicals• Neurotransmitters - chemical substance released from the end of a neuron during the propagation of a nerve impulse; it relays information from one neuron to another.• Neuromodulators – secreted in larger amounts and diffuse further (composed of peptides)• Hormones – produced in endocrine glands – released into extracellular fluid to be taken up by specific target cells
    • Binding• only specific neurotransmitters will bind with specific receptor sites – like a key in a lock• chemical that attaches to a binding site is a ligand• neurotransmitters are naturally produced ligands• neurotoxins are also ligands and various drugs have their effect in the same manner – artificially produced ligands (e.g., LSD)
    • Neurons – from electrical to chemical Only specific neurotransmitters will bind with the post-synaptic membrane.
    • Binding sitesAxodendritic – synapse on the dendrite of the neuronAxosomatic – synapse on the somaAxoaxonic – synapse on the axon Axodendritic Axosomatic Axoaxonic
    • Receptors• neurotransmitter specific postsynaptic receptors• open to allow ions to flow into the postsynaptic neuron• two main types • ionotropic • metabotropic
    • Ionotropic receptors• receptor site has its own ion channel• contain sodium channels• fast acting and short lasting
    • Metabotropic receptors• indirect method• located nearby G-proteins• G-proteins in turn activate an ion channel• slower to begin and longer lasting
    • Metabotropic receptors• G-proteins can also activate second messengers – enzymes that in turn activate an ion channel
    • Excitatory or inhibitory post-synaptic potentials.• once neurotransmitters are bound to the post synaptic membrane theelectrical charge is now altered in the receiving neuron • the change in the electric charge can be more positive than the resting potential (excitatory) or more Inhibitory negative than the resting potential (inhibitory)
    • Excitatory or inhibitory post-synaptic potentials.
    • Post-synaptic potentials• determined by the ion channel opened by the neurotransmitter and not the transmitter itself• graded – the potential dissipates with distance traveled• smaller in magnitude than action potentials• action potentials are always excitatory – post-synaptic potentials can be either excitatory or inhibitory
    • Post-synaptic potentials• excitatory PSP – typically related to sodium ion channels (rush of Na+ into the cell makes it more positively charged)• inhibitory PSP typically related to potassium ion channels (extra K+ maintained inside cell by sodium-potassium pump leaks out making the cell more negatively charged)• action of Cl– channels depends on the state of the receiving neuron – if depolarised Cl– will bring the cell back to a resting state
    • Terminating the PSP• reuptake – rapid removal of neurotransmitter from the synaptic cleft• SSRIs (selective seratonin reuptake inhibitors – e.g, Prozac) prolong the PSP by inhibiting reuptake
    • Summation of post-synaptic potentials.• whether the PSP leads to the excitation or inhibition of the neuron depends on the combined effects of many PSPs
    • Neural integrationSpatial integration: equal excitatory and inhibitory input will cause nochange
    • Neural integrationTemporal integration: ripples can combine to make bigger ripples
    • Autoreceptors• autoreceptors respond to neurotransmitters they produce• regulate synthesis and release of other transmitters• metabotropic• usually inhibitory – may control amount of neurotransmitter released
    • Other types of synapses• axoaxonic – modulate the neurotransmitters in the presynaptic neuron• gap junctions – electrical synapses – the synaptic cleft is much smaller – ions pass directly from one neuron to another
    • Why do you need to know all this?• different disease processes involve different aspects of the basic electrochemical transmission of neural information• Parkinson’s Disease – dopamine deficiency• Multiple Sclerosis – affects the myelin sheath of white matter• Epilepsy – abnormal electrical stimulation• Alzheimer’s Disease – neurofibrillary tangles may affect the transport of neurotransmitters
    • Review Questions1 ) NeuromodulatorsA) are rarely of a peptide form.B) are secreted from a neuron and only effect an adjacent neuron.C) are inevitably inhibitory.D) are secreted from neurons, but dispersed widely in the brain.E) are typically secreted in very small amounts compared to neurotransmitters.2 ) Most ________ are secreted into the extracellular fluid from endocrine glands or tissues.A) neurotransmittersB) neuropeptidesC) modulatorsD) hormonesE) Pheromones3 ) Large synaptic vesicles are produced in theA) soma.B) dendrites.C) terminal buttons.D) dendritic spines.E) neuroglia.
    • Review Questions4 ) Which of the following is true of neurotransmitter function?A) Neurotransmitters diffuse widely in the brain to exert changes in metabolism.B) Neurotransmitters directly alter ion channels using a second-messenger chemical.C) Neurotransmitters are released into the synapse from the cistaerna.D) Neurotransmitters open ion channels in the postsynaptic membrane.E) Neurotransmitters alter ion channel activity for minutes.5 ) Which of the following will produce an EPSP?A) opening a sodium channelB) closing a sodium channelC) opening a potassium channelD) opening a manganese channelE) closing a calcium channelNice review animation
    •  For Next TimeStart reading Chapter 3  Structure of the Nervous System
    •  Movie  Behaving Brain