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General Neurophysiology
Axonal transport
Transduction of signals at the cellular level
Degeneration and regeneration in the nervous system
Neurophysiological principles of behavior
Olga Vajnerová, Department of physiology, 2nd Medical School Charles University Prague
(axoplasmatic transport)
Anterograde
Proteosynthesis in the cell body only (ER, Golgi apparatus)
RetrogradeMoving the chemical signals from periphery
Axonal transport
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 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 cells
Tetanus toxin is released from the nerve cell body
Taken up by the terminals of neighboring neurons
http://cs.wikipedia.org/wiki/Vzteklina
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
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
Axon – the signal is carried without decrement
Threshold
All or nothing law
Dendrite and cell body – signal is propagated with decrement
Signal propagation from dendrite to initial segment
Origin of the AP
electrical stimulus
sensory input
neurotransmitter on synapses
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,
Phototransduction Chemotransduction Mechanotransduction
Sensory input
Sensory transduction – conversion of stimulus from the external or internal environment into an electrical signal
Signals: taste, light photon (vision), touch, pain, olfaction, muscle spindle,
Phototransduction Chemotransduction Mechanotransduction sound wave (auditory),
Sensory input
Sensory transduction – conversion of stimulus from the external or internal environment into an electrical signal
Signals: light photon (vision), touch, pain, olfaction, muscle spindle,
Phototransduction Chemotransduction taste,
Mechanotransduction sound wave (auditory),
Sensory input
Sensory transduction – conversion of stimulus from the external or internal environment into an electrical signal
Signals: touch, pain, olfaction, muscle spindle,
Phototransduction light photon (vision),
Chemotransduction taste,
Mechanotransduction sound wave (auditory),
Sensory input
Sensory transduction – conversion of stimulus from the external or internal environment into an electrical signal
Signals: pain, olfaction, muscle spindle,
Phototransduction light photon (vision),
Chemotransduction taste,
Mechanotransduction sound wave (auditory), touch,
Sensory input
Sensory transduction – conversion of stimulus from the external or internal environment into an electrical signal
Signals:, olfaction, muscle spindle,
Phototransduction light photon (vision),
Chemotransduction taste, pain
Mechanotransduction sound wave (auditory), touch,
Sensory input
Sensory transduction – conversion of stimulus from the external or internal environment into an electrical signal
Signals: muscle spindle,
Phototransduction light photon (vision),
Chemotransduction taste, pain olfaction
Mechanotransduction sound wave (auditory), touch,
Sensory input
Sensory transduction – conversion of stimulus from the external or internal environment into an electrical signal
Signals:,
Phototransduction light photon (vision),
Chemotransduction taste, pain olfaction
Mechanotransduction sound wave (auditory), touch, muscle spindle
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
Origin of the AP
electrical stimulus
sensory input
neurotransmitter on 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+ channelsmembrane depolarization
• Inhibitory receptors open K+, Cl- channels
membrane hyperpolarization
• EPSP – excitatory postsynaptic potential
• IPSP – inhibitory postsynaptic potential
Excitatory and inhibitory postsynaptic potential
Interaction of synapses
Summation of signalsspatial and temporal
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
Transduction of signals at the cellular level
EPSPIPSP
Initial segment AP Ca2+ influx
Neurotransmitter
Neurotransmitter releasing
Neuronal activity in
transmission of signals
Discharge configurationsof various cells
EPSPIPSP
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
RMP
Threshold
Hammond, C.:Cellular and Molecular Neurobiology.
Academic Press, San Diego 2001: str. 407.
Myelin sheath of axons in PNS(a membranous wrapping around the axon)
Degeneration and regeneration in the nervous system
Myelin sheath of axons in PNS(a basal lamina)
Basal lamina
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
Myelin sheath formation in CNS
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
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
Neurophysiological principles of behavior
Ivan Petrovich PavlovRussia nobelist 1904
Research on reflexes
Sir Charles Scott SherringtonGreat Britain nobelist 1932
Reflex arch
Knee-jerk reflex
Behavior as a chain of reflexes?
LOCUSTTwo 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 wingsCut of the wingsRemoved other parts of locust s body that contained sense organsUnexpected resultMotor 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 patternLocust flight systém did not require sensory feedback to provide timing cues for rhythm generation
Network of neuronsOscillator, pacemaker, central pattern generator
Central pattern generatorModel 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.
SwimmingWing beatingWalkingGallop, trotLickingScratchingBreathingChewing
Fixed action pattern innate endogenous fireing activity produced by a
specific neural network
Simple external sensory stimulus release complex activity
An instinctive behavioral sequence that is indivisible and runs to completion
stimulus known as a sign stimulus (releaser) – consumatory behavior
Greylag goose will roll a displaced egg near its nest back to the others with its beak. The sight of the displaced egg
triggers this mechanism. If the egg is taken away, the animal continues with the
behavior, pulling its head back as if an imaginary egg is still being maneuvered by
the underside of its beak
The egg rolling behavior of a
Greylag Goose
Neurophysiological principles of behavior - summary
Innate forms of behavior
•Unconditioned reflex
•An instinctive behavioral sequence
•Central pattern generator
Acquired forms of behavior
Learning and memory
(conditioned reflex)
Neurophysiological principles of behavior - summary
Innate forms of behavior
•Unconditioned reflex
•An instinctive behavioral sequence
•Central pattern generator
Acquired forms of behavior
Learning and memory
(conditioned reflex)
Taste stimulus – salivation, mimic expresion for anger, bike riding, breathing movements, vizual stimulus - salivation
Neurophysiological principles of behavior - summary
Innate forms of behavior
•Unconditioned reflex Taste stimulus – salivation
•An instinctive behavioral sequence mimic expresion for
anger
•Central pattern generator breathing movements
Acquired forms of behavior
Learning and memory bike riding
(conditioned reflex vizual stimulus -
salivation)
,,,,
conditioned reflex : salivation - visual stimulus
Thanks for attention