General Neurophysiology

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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
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Axonal transport

(axoplasmatic transport) Anterograde Proteosynthe
sis in the cell body only (ER, Golgi
apparatus) Retrograde Moving the chemical
signals from periphery
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Anterograde axonal transport fast (100 - 400
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 (50 - 250
mm/day) MAP dynein/ mikrotubules old
mitochondria, vesicles (pinocytosis,
receptor-mediated endocytosis in axon terminals,
transport of e.g. growths factors),
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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
http//cs.wikipedia.org/wiki/Vzteklina
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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 Horseradi
sh 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
 

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Transduction of signals at the cellular level
Somatodendritic part passive conduction of the
signal, with decrement
Axonal part action potential, spreading without
decrement, all-or-nothing law
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Resting membrane potential
Every living cell in the organism
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Membrane potential is not a potential. It is a
difference of two potentials so it is a voltage,
in fact.
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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
Na
Cl-
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Transduction of signals at the cellular level
Axonal part action potential, spreading without
decrement, all-or-nothing law

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Axon the signal is carried without decrement
Threshold All or nothing law
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Action potential
Membrane conductance for Na a pro K
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Action potential

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Propagation of the action potential along the axon
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Transduction of signals at the cellular level
Somatodendritic part passive conduction of the
signal, with decrement
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Dendrite and cell body signal is propagated
with decrement
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Signal propagation from dendrite to initial
segment
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Origin of the electrical signal electrical
stimulus sensory input neurotransmitter on
synapses
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Axonal part of the neuronAP 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.
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Somatodendritic part of neuron

• Receptors on the postsynaptic membrane
• Excitatory receptors open Na, Ca2
  channels membrane depolarization
• Inhibitory receptors open K, Cl- channels
• membrane hyperpolarization
• EPSP excitatory postsynaptic potential
• IPSP inhibitory postsynaptic potential

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Excitatory and inhibitory postsynaptic potential
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Interaction of synapses
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Summation of signals spatial and temporal
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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


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Transduction of signals at the cellular level
EPSP IPSP
Initial segment
AP
Ca2 influx
Neurotransmitter
Neurotransmitter releasing
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Neuronal activity in transmission of signals
Discharge configurationsof various cells
EPSP IPSP
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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
dendrites 3.AHP, after-hyperpolarization, Ca2
sensitive K channels 4.Rebound depolarization,
low threshold Ca2 channels, (probably localized
at the level of the soma
Threshold
RMP
Hammond, C.Cellular and Molecular Neurobiology.
Academic Press, San Diego 2001 str. 407.
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Origin of the electrical signalelectrical
stimulussensory inputneurotransmitter on
synapses
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Sensory input
Sensory transduction conversion of stimulus
from the external or internal environment into an
electrical signal
Phototransduction
Chemotransduction
Mechanotransduction
Signals sound wave (auditory), taste, light
photon (vision), touch, pain, olfaction, muscle
spindle,
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Sensory input
Sensory transduction conversion of stimulus
from the external or internal environment into an
electrical signal
Phototransduction light photon (vision),
Chemotransduction taste,
pain olfaction
Mechanotransduction sound wave (auditory), touch,
muscle spindle
Osmoreceptors, thermoreceptors
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Classification of nerve fibres
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The compound action potential
Program neurolab
Diferences between the velocities of individual
fibres give rise to a dispersed compoud action
potential
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Compound action potential all types of nerve
fibres
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Classification of nerve fibres
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Classification of nerve fibres
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Two different systems are in use for classifying
nerve fibres
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Myelin sheath of axons in PNS(a membranous
wrapping around the axon)
Degeneration and regeneration in the nervous
system
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Myelin sheath of axons in PNS(a basal lamina)
Basal lamina
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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

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Myelin sheath formation in CNS
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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

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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