Synaptic integration and plasticity Flashcards
Whats signal transduction?
Changed in ionic gradient/ membrane potential such as action potentials have to be transduced in order to produce physiological actions
Whats a classic example of signal transduction?
Synaptic transmission
Transduction of voltage changes to biochemical changes result in what?
Synaptic release
Excitation-contraction coupling
What are the steps to quantal synaptic transmission?
- Transmitter is synthesised and then stored in vesicles
- An AP invades the presynaptic terminal
- Depolarisation of presynaptic terminal causes opening of Voltage-gated Ca2+ channels
- Influx of Ca2+ through channels
- Ca2+ causes vesicles to fuse with presynaptic membrane
- Transmitter is released into synaptic cleft via exocytosis
- Transmitter binds to receptor molecules in postsynaptic membrane
- Opening or closing of postsynaptic channels
- postsynaptic current causes excitatory or inhibitory postsynaptic potential that changes the excitability of the postsynaptic cell
- Retrieval of vesicular membrane from plasma membrane
Whats quantal synaptic release?
Quantal release is the mechanism by which most traditional endogenous neurotransmitters are transmitted throughout the body
Tell me about transmission and neuromusuclar junction- nmj/ quantal release ACh
- Ach released due to Ca2+ current
- Cholinergic receptor present is nicotinic (nicotinic for muscle not the muscarinic receptor)
- End plate potential: excitatory, post-synaptic potential
What are end plate potentials (EPPs)?
End plate potentials (EPPs) are the voltages which cause depolarization of skeletal muscle fibres caused by neurotransmitters binding to the postsynaptic membrane in the neuromuscular junction. They are called “end plates” because the postsynaptic terminals of muscle fibres have a large, saucer-like appearance
What are the functional properties and synaptic ‘chemical’ transmission?
- Synaptic transmission is Ca2+-dependent - proven by use of buffers inside or outside
- Synaptic transmission is quantised
- Can be blocked by antagonists e.g. tubocurarine
- Can be excitatory or inhibitory – essential to processes of neurocomputation
In order for information to pass from one neuron to the next, what must happen?
- The information must cross both the pre- and post- synaptic membranes
- The AP signals in the axon must be transduced into release of neurotransmitter
What is the size of the post-synaptic response related to?
The number and timing of pre-synaptic APs- intensity coding
Diagrammatic outlin of cell-to-cell information transfer within the nervous system
Name an inhibitory and excitatory synapse?
Inhibitory: GABA/glycine
Excitatory: Glutamatergic
Excitatory and inhibitory synapses, what do each of these have a flux of?
Are they symmetric or asymmetric
Glutamatergic= excitatory= flux of Na+/Ca2+ ions
GABA/ glycine= inhibitory= flux of Cl-
What do glutamate receptors produce?
What do GABA receptors produce?
Number 5, the AP itself does not cross the chemical synapse. Ca2+ current triggers chemical transmission, this causes an EPSPs. summation of EPSPs causes the AP. Some are electrical synapses (but are relatively rare in the mammalian CNS)
Why is there integration of synaptic potentials?
- Neurons receive multiple synaptic inputs
- The resulting currents are summed by the cell, integrating the input information
- The net effect of these inputs modified the output of the neuron
A synaptically induced potential can increase and decrease what?
It can increase the neuronal conductance (decrease in membrane resistance)
It can decrease the effectiveness of an excitatory input- “shunting” its effect and reducing excitation
What factors are involved with Neurocomputation (synaptic potential to AP conversion)?
- MODALITY info from which neurone activated
- MAGNITUDE info from the number and timing of APs transmitted
- Temporal Summation / Spatial Summation
- Non-Linear Coding of summed synaptic/ generator potential to AP production
What are temporal summation of EPSPs?
Successive synaptic inputs that occur before the neurone has had time to fully recover can sum together to produce a greater overall effect
Whats spatial summation?
Multiple inputs into one neuron
Multiple synaptic inputs on to different parts of the neurone can sum together to produce a greater overall effect
What do temporal and spatial summation produce?
Graded post-synaptic depolarisations
What do greater post-synaptic depolarisations produce?
Multiple APs
- AP frequency is roughly proprotional to the log of the stimulus intensity up to a maximum
- Recruitment of other neurons increases dynamic range of system
Whats meant by Convergence of a neuronal pathway?
Neuronal pathways may lead to signals from multiple neurones converging onto a single target neurone - CONVERGENCE
Whats meant by divergence of a neural pathway?
Neuronal pathways carrying signals from a single neurone being sent onto multiple neurones - DIVERGENCE
Give an example of convergence in neuronal pathways?
e.g. convergence in retina
Rods = high convergence = low acuity
Cones = low convergence = high acuity
Give an example of divergence in a neuronal pathway?
e.g. divergence- crossed extensor reflex
Also, one α-motor neuron to multiple muscle fibres
Give an example of two things that synaptic plasticity can lead to?
- Long-term potentiation LTP
- Long- term depression LTD
Tell me about long-term potentiation?
- Stimulus Trains of high frequency pulses (c.100Hz) to CA1 POTENTIATE responses to single test stimuli
- Extracellular stimuli activate multiple parallel axons and hence multiple synapses to same Post-Synaptic Cell summating excitation
- Forces CONTIGUITY of Pre- and Post-synaptic activity
Tell me about long-term depression?
- Studies in small repeated circuits within larger system e.g. cerebellum
- Pairing stimulation of climbing fibres (CF) and parallel fibres (PF) causes Long Term Depression that reduces the parallel fibre EPSP
Whats quantal release?
basically, the idea that the neurotransmitters are released in discrete quantities
