Transcript 2015 - Univerzita Karlova v Praze

General Neurophysiology
Axonal transport
Transduction of signals at the cellular level
Classification of nerve fibres
Reflexes and pattern generation
Olga Vajnerová, Department of physiology,
2nd Medical School Charles University
Prague
Axonal transport
(axoplasmatic transport)
Anterograde
Proteosynthesis in the cell body
only (ER, Golgi apparatus)
Retrograde
Moving the chemical signals from
periphery
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),
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.o
rg/wiki/Vzteklina
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
Transduction of signals at the
cellular level
Somatodendritic part –
passive conduction
of the signal, with decrement
Axonal part –action potential,
spreading without decrement, all-ornothing law
Resting membrane potential
Every living cell
in the organism
Membrane potential is not a potential. It
is a difference of two potentials so it is a
voltage, in fact.
When the membrane would be permeable for K+
only
• K+ escapes out of
the cell along
concetration
gradient
K+
-
-
+
+
+
+
Ai
• A- cannot leave the
cell
K+
+
Na+
Cl-
• Greater number of
positive charges is
on the outer side
of the membrane
Action potential
Axonal part –action potential
Threshold stimulus
Axon – the signal is carried without decrement
All or nothing law
Origin of the AP
electrical stimulus
or
depolarisation of initial segment
Dendrite and cell body – signal is propagated with decrement
Signal propagation from dendrite to initial segment
Excitation or inhibition of dendrites and soma
SYNAPSES
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.
Somatodendritic part of neuron
Receptors on the postsynaptic membrane
• Excitatory receptors open Na+, Ca2+ channels
depolarization
• Inhibitory receptors open K+, Cl- channels
membrane hyperpolarization
• EPSP – excitatory postsynaptic potential
• IPSP – inhibitory postsynaptic potential
membrane
Excitatory and inhibitory postsynaptic potential
Interaction of synapses
Summation of signals
spatial and temporal
Potential changes in the
area of trigger zone (axon
hillock)
Trigger zone
• 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
Transduction of signals at the cellular
level
2. EPSP
3. Initial
IPSP
segment
depolarisation
1. Synapse
Neurotransmitter
4. AP
5. Ca2+ influx
1. Neurotransmitter
releasing
EPSP
IPSP
Neuronal
activity in
transmission
of signals
Discharge
configurations
of various cells
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.
Classification of nerve fibres
The compound action potential
Program neurolab
Biphasic recording from whole nerve
Differences between the velocities of
individual fibres give rise to a dispersed
compound action potential
Compound action potential – all types of nerve fibres
Classification of nerve fibres
Classification of nerve fibres
Two different systems are
in use for classifying nerve
fibres
General Neurophysiology
Axonal transport
Transduction of signals at the cellular level
Classification of nerve fibres
Reflexes and pattern generation
Research on reflexes
Ivan Petrovich Pavlov
Russia
nobelist 1904
Sir Charles Scott Sherrington
Great Britain
nobelist 1932
Reflex arch
Knee-jerk reflex
Behavior as a chain of reflexes?
LOCUST
Two pairs of wings
Each pair beat in synchrony
but the rear wings lead the
front wings in the beat cycle
by about 10%
Proper delay between
contractions of the front and
rear wing muscles
Donald Wilson’s Experiment in 1961
To confirm the hypothesis
Identify the reflexes that are responsible for the flight pattern
Deafferentaion = the elimination of sensory input into the CNS
Remove sense organs at the bases of the wings
Cut of the wings
Removed other parts of locust s body that contained sense organs
Unexpected result
Motor signals to the flight muscles still came at the proper time to keep the wings beat
correctly synchronized
Extreme experiment
Reduced the animal to a head and the floor of the thorax and the thoracic nerve
cord
Elecrodes on the stumps of the nerves that had innervated the removed flight
muscles
Motor pattern recorded in the absence of any movement of part of animal – fictive
pattern
Locust flight systém did not require sensory feedback to provide timing cues for
rhythm generation
Network of neurons
Oscillator, pacemaker, central pattern generator
Central pattern
generator
Model of the CPG for control of muscles
during swimming in lamprey
Central pattern generators
A network of neurons capable of producing a properly timed pattern of
motor impulses in the absence of any sensory feedback.
Swimming
Wing beating
Walking
Gallop, trot
Licking
Scratching
Breathing
Chewing
Summary
Classification of nerve fibres
Summary
Transduction of signals at the cellular level
2. EPSP
3. Initial
IPSP
segment
depolarisation
1. Synapse
Neurotransmitter
4. AP
5. Ca2+ influx
Neurotransmitter
releasing
Questions?