Lecture 7: Synapses and Networks Flashcards
What is the neuron doctrine?
- Brains are composed of separate neurons and other cells
- Cells are independent
- Neurons are polarised cells
- Information is transmitted from cell to cell across tiny gaps
What happens at a synapse?
At a synapse signals are transmitted to another neuron
What are the three typical locations of synaptic processes?
- Axo-dendritic
- Axo-somatic
- Axo-axonic
What is an axo-dendritic synapse?
a type of synapse where the axon of one neuron connects with the dendrite of another neuron,
What is an axo-somatic synapse?
a type of synapse where the axon terminal of one neuron makes contact with the cell body (soma) of another neuron, often having an inhibitory effect.
What is an axo-axonic synapse?
a type of synapse where the axon terminal of one neuron makes contact with the axon of another neuron, allowing for direct regulation of neurotransmitter release from the postsynaptic axon terminal.
Which is more common; a chemical or electric synapse?
Chemical
What is the difference between chemical and electric synapses?
Electrical synapses use direct physical connections (gap junctions) for rapid signal transmission, while chemical synapses rely on neurotransmitters released into a gap to transmit signals
How is information coded?
Through the interaction of neurons
What is a single neuron’s function?
To transmit or not transmit a neuronal signal
Presynaptic neuron shoots action potential to postsynaptic neuron. If successful depolarisation occurs
Explain the steps of the signal transformation during synaptic transmission?
- Presynaptic neuron: Depolarisation of the axonal terminal membrane opens Ca2+ channels and Ca2+ ions enter the terminal
- Presynaptic neuron: The increase in Ca2+ concentration stimulates the release of neurotransmitter that is stored in vesicles. When these vesicles fuse with presynaptic membrane the neurotransmitter diffuses into the synaptic cleft
- Postsynaptic neuron: Ionotropic receptors that are embedded in the membrane of the dendrite or soma (typically) of the postsynaptic neuron…
What are examples of amins?
acetylcholin [nicotinic, nACh receptors, serotonin (5-HT)
What are examples of amino acids?
glutamate (e.g. NMDA and AMPA receptors), gamma-aminobutyric acid (GABA A), glycine, aspartate
What are the two types of receptors?
- Ionotropic receptors
- Metabotropic receptors
What are ionotropic receptors?
also known as ligand-gated ion channels, are transmembrane proteins that open to allow ions to pass through the cell membrane in response to the binding of a chemical messenger, like a neurotransmitter.
What are metabotropic receptors?
also known as G-protein-coupled receptors (GPCRs), are membrane receptors that initiate a series of intracellular events, often involving second messengers, to modulate cell activity, unlike ionotropic receptors which directly form ion channels.
What is the major difference between ionotropic and metabotropic receptors?
Ionotropic receptors are ligand-gated ion channels that directly mediate ion flow upon neurotransmitter binding, while metabotropic receptors are G-protein-coupled receptors that initiate signaling cascades via second messengers, indirectly affecting ion channels and other cellular processes.
What is the in the postsynaptic membrane?
- Ionotropic receptor
- Metabotropic receptor
What is in the presynaptic membrane?
- Reuptake transporter
- Auto-receptor
- Hetero-receptor
What is in the synapse?
Enzymes - for degradation which breaks down used neurotransmitters in the synapse
When and which signal is picked up by a neuron depends on the…
- Type of synapse and associated neurotransmitter (excitatory or inhibitory synapse)
- Number of synapses and spatial position on the dendrites/soma of the input zone
- Duration and synchrony of neurotransmitter release from different synapses
What typical transmitters are at excitatory synapses?
Glutamate, aspartate, nicotinic acetylcholine (nACh), muscarinic Ach (slow EPSPs)
What typical transmitters are at inhibitory synapses?
GABA, glycine, muscarinic acetylcholine
What is temporal summation?
If the neurotransmitter is released for longer time into the synaptic cleft, then the postsynaptic potential is stronger
What is spatial summation?
Is postsynaptic potentials arrive together in the integration zone, they are summed up
What are spiking neurons?
If the membrane at the integration zone is depolarised above the threshold an action potential will be generated.
The more excitatory input arrives, the stronger the output signal
How is information coded in the neural networks?
Spatial and temporal summation at the synapses determine how the signal travels through a network
The connectivity of the network (connectome) determines when or where a signal travels faster or slower, is amplified or reduced, or muted.
What are divergence neurons?
Divergence allows one neuron to communicate with many other neurons in a network.
What are convergence neurons?
Convergence allows a neuron to receive input from many neurons in a network.
What are deep neural networks?
DNNs have been shown to predict experimental outcomes (e.g. human perceptual similarity judgements, neural activity in primate sensory cortices)
