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General Neurophysiology Axonal transport Transduction of signals at the cellular level Classification of nerve fibres Olga Vajnerová, Department of physiology,

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Presentation on theme: "General Neurophysiology Axonal transport Transduction of signals at the cellular level Classification of nerve fibres Olga Vajnerová, Department of physiology,"— Presentation transcript:

1 General Neurophysiology Axonal transport Transduction of signals at the cellular level Classification of nerve fibres Olga Vajnerová, Department of physiology, 2nd Medical School Charles University Prague

2 (axoplasmatic transport) Anterograde Proteosynthesis in the cell body only (ER, Golgi apparatus) Retrograde Moving the chemical signals from periphery Axonal transport

3 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 cell Axon terminal (endocytosis) Retrograde transport to the cell body Neurons produce copies of the virus CNS – behavioral changes Neurons innervating the salivary glands (anterograde transport) Tetanus toxin (produced by Clostridium tetani) Toxin is transported retrogradely in nerve cells Tetanus toxin is released from the nerve cell body Taken up by the terminals of neighboring neurons rg/wiki/Vzteklina

5 Axonal transport as a research tool Tracer studies (investigation of neuronal connections) Anterograde axonal transport Radioactively 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 distribution Retrograde axonal transport Horseradish 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 Axonal part –action potential, spreading without decrement, all-or-nothing law Somatodendritic part – passive conduction of the signal, with decrement

7 Resting membrane potential Every living cell in the organism

8 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 gradient A - cannot leave the cell Greater number of positive charges is on the outer side of the membrane K+K+ AiAi Na+ Cl- K+

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 Threshold All or nothing law

12 Membrane conductance for Na + a pro K + Action potential

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14 Propagation of the action potential along the axon

15 Transduction of signals at the cellular level Somatodendritic part – passive conduction of 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 Ca 2+ channels –neurotransmitter release Arrival of an AP in the terminal opens voltage- gated Ca 2+ channels, causing Ca 2+ influx, which in turn triggers transmitter release.

20 Somatodendritic part of neuron Receptors on the postsynaptic membrane Excitatory receptors open Na +, Ca 2+ channels membrane depolarization Inhibitory receptors open K +, Cl - channels membrane hyperpolarization EPSP – excitatory postsynaptic potential IPSP – inhibitory postsynaptic potential

21 Excitatory and inhibitory postsynaptic potential

22 Interaction of synapses

23 Summation of signals spatial and temporal

24 Potential changes in the area of trigger zone (axon hillock) Interaction of all synapses Spatial summation – currents from multiple inputs add algebraically up Temporal summation –if another APs arrive at intervals shorter than the duration of the EPSP Trigger zone

25 Transduction of signals at the cellular level EPSP IPSP Initial segment AP Ca2+ influx Neurotransmitter Neurotransmitter releasing

26 Neuronal activity in transmission of signals Discharge configurations of various cells EPSP IPSP

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 Ca 2+ channels, localized in the dendrites 3.AHP, after-hyperpolarization, Ca 2+ sensitive K + channels 4.Rebound depolarization, low threshold Ca 2+ channels, (probably localized at the level of the soma RMP Threshold Hammond, 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 input Sensory transduction – conversion of stimulus from the external or internal environment into an electrical signal Signals: sound wave (auditory), taste, light photon (vision), touch, pain, olfaction, muscle spindle, PhototransductionChemotransductionMechanotransduction

30 Sensory input Sensory transduction – conversion of stimulus from the external or internal environment into an electrical signal Osmoreceptors, thermoreceptors Phototransduction light photon (vision), Chemotransduction taste, pain olfaction Mechanotransduction sound wave (auditory), touch, muscle spindle

31 Classification of nerve fibres

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33 The compound action potential Diferences between the velocities of individual fibres give rise to a dispersed compoud action potential Program neurolab

34 Compound action potential – all types of nerve fibres

35 Classification of nerve fibres

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38 Two different systems are in use for classifying nerve fibres

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41 Myelin sheath of axons in PNS (a membranous wrapping around the axon) Degeneration and regeneration in the nervous system

42 Myelin sheath of axons in PNS (a basal lamina) Basal lamina

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 functionem Compression, crushing – good, Schwann cells remain in their original orientation, axons can find their original targets Cutting – worse, regeneration is less likely to occure

44 Myelin sheath formation in CNS

45 Injury of the axon in CNS Oligodendrocytes do not create a basal lamina and a band of Büngner Regeneration to a functional state is impossible Trauma of the CNS proliferation and hypertrophy of astrocytes, astrocytic scar

46 Injury of the axon in PNS after amputation Amputation of the limb Proximal stump fail to enter the Schwann cell tube, instead ending blindly in connective tissue Blind ends rolle themselves into a ball and form a neuroma – phantom pain


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