Presentation on theme: "General Neurophysiology"— Presentation transcript:
1 General Neurophysiology Axonal transportTransduction of signals at the cellular levelClassification of nerve fibresOlga Vajnerová, Department of physiology, 2nd Medical School Charles University Prague
2 Axonal transport (axoplasmatic transport) Anterograde Proteosynthesis in the cell body only (ER, Golgi apparatus)RetrogradeMoving the chemical signals from periphery
3 Anterograde axonal transport Anterograde axonal transport fast ( mm/day) MAP kinesin/mikrotubules moves neurotransmitters in vesicles and mitochondria slow (0,5 – 10 mm/day) unknown mechanism structural components (cytoskeleton - aktin, myosin, tubulin), metabolic components Retrograde axonal transport fast ( mm/day) MAP dynein/ mikrotubules old mitochondria, vesicles (pinocytosis, receptor-mediated endocytosis in axon terminals, transport of e.g. growths factors),
4 Axonal transport in the pathogenesis of diseases Rabies virus (madness, hydrofobia)Replicates in muscle cellAxon terminal (endocytosis)Retrograde transport to the cell bodyNeurons produce copies of the virusCNS – behavioral changesNeurons innervating the salivary glands (anterograde transport)Tetanus toxin (produced by Clostridium tetani)Toxin is transported retrogradely in nerve cellsTetanus toxin is released from the nerve cell bodyTaken up by the terminals of neighboring neuronsRabies, madness, hydrophobia: viral neuroivasive desease, encephalitis, incubation period several month,symptoms malaise, excitement, depression, pain, paresis, unable to swallow water, mania lethargy, coma, respiratory insufficiency
5 Axonal transport as a research tool Tracer studies (investigation of neuronal connections)Anterograde axonal transportRadioactively labeled amino acids (incorporated into proteins, transported in an anterograde direction, detected by autoradiography)Injection into a group of neuronal cell bodies can identify axonal distributionRetrograde axonal transportHorseradish peroxidase is injected into regions containing axon terminals. Is taken up and transported retrogradely to the cell body. After histology preparation can be visualized.Injection to axon terminals can identify cell body
6 Transduction of signals at the cellular level Somatodendritic part –passive conductionof the signal, with decrementAxonal part –action potential, spreading without decrement, all-or-nothing law
7 Resting membrane potential Every living cellin the organism
8 Membrane potential is not a potential Membrane potential is not a potential. It is a difference of two potentials so it is a voltage, in fact.
9 When the membrane would be permeable for K+ only K+ escapes out of the cell along concetration gradientA- cannot leave the cellGreater number of positive charges is on the outer side of the membraneK+Ai+-K+Na+Cl-
10 Transduction of signals at the cellular level Axonal part –action potential, spreading without decrement, all-or-nothing law
11 Axon – the signal is carried without decrement ThresholdAll or nothing law
12 Action potentialMembrane conductance for Na+ a pro K+
14 Propagation of the action potential along the axon
15 Transduction of signals at the cellular level Somatodendritic part –passive conductionof the signal, with decrement
16 Dendrite and cell body – signal is propagated with decrement
17 Signal propagation from dendrite to initial segment
18 Origin of the electrical signal electrical stimulus sensory input neurotransmitter on synapses
19 Axonal part of the neuron AP – voltage-gated Ca2+ channels –neurotransmitter release Arrival of an AP in the terminal opens voltage-gated Ca2+ channels,causing Ca2+ influx,which in turn triggers transmitter release.
20 Somatodendritic part of neuron Receptors on the postsynaptic membraneExcitatory receptors open Na+, Ca2+ channels membrane depolarizationInhibitory receptors open K+, Cl- channelsmembrane hyperpolarizationEPSP – excitatory postsynaptic potentialIPSP – inhibitory postsynaptic potential
21 Excitatory and inhibitory postsynaptic potential
24 Potential changes in the area of trigger zone (axon hillock) Interaction of all synapsesSpatial summation – currents from multiple inputs add algebraically upTemporal summation –if another APs arrive at intervals shorter than the duration of the EPSPTrigger zone
25 Transduction of signals at the cellular level EPSPIPSPInitial segmentAPCa2+ influxNeurotransmitterNeurotransmitter releasing
26 Neuronal activity in transmission of signals Discharge configurations of various cells EPSPIPSP
27 Influence of one cell on the signal transmission 1.AP, activation of the voltage-dependent Na+ channels (soma, area of the initial segment)2. ADP, after-depolarization, acctivation of a high threshold Ca2+ channels, localized in the dendrites3.AHP, after-hyperpolarization, Ca2+ sensitive K+ channels4.Rebound depolarization, low threshold Ca2+ channels, (probably localized at the level of the somaThresholdRMPHammond, C.:Cellular and Molecular Neurobiology. Academic Press, San Diego 2001: str. 407.
28 Origin of the electrical signal electrical stimulus sensory input neurotransmitter on synapses
29 Sensory inputSensory transduction – conversion of stimulus from the external or internal environment into an electrical signalPhototransductionChemotransductionMechanotransductionSignals: sound wave (auditory), taste, light photon (vision), touch, pain, olfaction, muscle spindle,
30 Sensory inputSensory transduction – conversion of stimulus from the external or internal environment into an electrical signalPhototransduction light photon (vision),Chemotransduction taste, pain olfactionMechanotransduction sound wave (auditory), touch, muscle spindleOsmoreceptors, thermoreceptors
43 Injury of the axon in PNS Compression, crushing, cutting – degeneration of the distal axon - but the cell body remains intact (Wallerian degeneration, axon is removed by macrophages)Schwann cells remain and their basal lamina (band of Büngner)Proximal axon sprouts (axonal sprouting)Prognosis quo ad functionemCompression, crushing – good, Schwann cells remain in their original orientation, axons can find their original targetsCutting – worse, regeneration is less likely to occure
45 Injury of the axon in CNS Oligodendrocytes do not create a basal lamina and a band of BüngnerRegeneration to a functional state is impossibleTrauma of the CNSproliferation and hypertrophy of astrocytes, astrocytic scar
46 Injury of the axon in PNS after amputation Amputation of the limbProximal stump fail to enter the Schwann cell tube, instead ending blindly in connective tissueBlind ends rolle themselves into a ball and form a neuroma – phantom pain
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