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Summary Synaptic transmission part 1
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organisation of the nervous system
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Synaptic transmission part 2
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Lecture 3 : Synaptic transmission part 1Signal transfer btw neuronal cells - premises :
1) AP propagate over long distance, single nerve axon
2) Cell-to-cell transfer of electrical signals (AP) by synaptic transmission/ main types of intercellular
transmission
● Electrical synapses
○ direct electrical continuity btw cells, instantaneous signal transduction
○ gap junction
■ 2 connexons
■ opens when : elevated level of intracellular Ca2+ or H+ in one cell or in
response to depolarization of one or both cells.
○ low-resistance path for electrotonic current
○ little attenuation of the voltage signal
○ transmit signal in both direction, bidirectional with equal efficiency = reciprocal
synapses
○ sometimes conduct more in one direction than in another = rectifying synapses
○ can also transmit metabolic signals btw cells (ATP, cAMP,Ca2+,etc)
○ location
■ Inhibitory neurons of the Cerebral cortex + Thalamus
■ Excitatory neurons of : brainstem
■ other : hypothalamus/ basal ganglia/ spinal cord
○ Connect both neurons and glial cells
■ found in
● dendro-dendritic sites to synchronize the activity of neuronal
population
● more common in embryonic nervous system
● Chemical synapses
○ most of the synapses in the CNS
○ contiguity, no continuity btw neurons and neurotransmitters
○ btw pre- post synaptic segments, 1msc delay
○ >40 neurotransmitters discovered, most known are
■ Ach ■ GABA
■ norepinephrine ■ glycine
■ epinephrine ■ serotonin
■ histamine ■ glutamate
○ the most common synaptic arrangements in the CNS
■ axodendritic/ axospinous > 90% of excitatory synapses in the CNS
■ axosomatic
■ axoaxonic
■ dendrodendritic
■ somato somatic
■ somato-dendritic
3) other types of information transmission
● Volume transmission
○ neurotransmitter diffusion in the extracellular space
○ acts on extra-synaptic receptors
● Ephaptic transmission
○ electric fields generated by a specific neuron can alter the excitability of neighboring
neurons as a result of their anatomical and electrical proximity
synaptic function of neurons
- Information -> AP transmission through a succession of neurons, that can be :
1) blocked from one neuron to the next
2) changed from a single impulse into a repetitive impulses
3) integrated w impulses from other neurons in neuronal networks, to cause highly intricate
patterns of impulses in successive neurons
1
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