Lecture 7: Synapses and Networks

Question 1

What is the neuron doctrine?

Answer 1

1. Brains are composed of separate neurons and other cells
2. Cells are independent
3. Neurons are polarised cells
4. Information is transmitted from cell to cell across tiny gaps

Question 2

What happens at a synapse?

Answer 2

At a synapse signals are transmitted to another neuron

Question 3

What are the three typical locations of synaptic processes?

Answer 3

1. Axo-dendritic
2. Axo-somatic
3. Axo-axonic

Question 4

What is an axo-dendritic synapse?

Answer 4

a type of synapse where the axon of one neuron connects with the dendrite of another neuron,

Question 5

What is an axo-somatic synapse?

Answer 5

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.

Question 6

What is an axo-axonic synapse?

Answer 6

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.

Question 7

Which is more common; a chemical or electric synapse?

Answer 7

Chemical

Question 8

What is the difference between chemical and electric synapses?

Answer 8

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

Question 9

How is information coded?

Answer 9

Through the interaction of neurons

Question 10

What is a single neuron’s function?

Answer 10

To transmit or not transmit a neuronal signal

Presynaptic neuron shoots action potential to postsynaptic neuron. If successful depolarisation occurs

Question 11

Explain the steps of the signal transformation during synaptic transmission?

Answer 11

1. Presynaptic neuron: Depolarisation of the axonal terminal membrane opens Ca2+ channels and Ca2+ ions enter the terminal
2. 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
3. Postsynaptic neuron: Ionotropic receptors that are embedded in the membrane of the dendrite or soma (typically) of the postsynaptic neuron…

Question 12

What are examples of amins?

Answer 12

acetylcholin [nicotinic, nACh receptors, serotonin (5-HT)

Question 13

What are examples of amino acids?

Answer 13

glutamate (e.g. NMDA and AMPA receptors), gamma-aminobutyric acid (GABA A), glycine, aspartate

Question 14

What are the two types of receptors?

Answer 14

1. Ionotropic receptors
2. Metabotropic receptors

Question 15

What are ionotropic receptors?

Answer 15

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.

Question 16

What are metabotropic receptors?

Answer 16

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.

Question 17

What is the major difference between ionotropic and metabotropic receptors?

Answer 17

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.

Question 18

What is the in the postsynaptic membrane?

Answer 18

• Ionotropic receptor
• Metabotropic receptor

Question 19

What is in the presynaptic membrane?

Answer 19

• Reuptake transporter
• Auto-receptor
• Hetero-receptor

Question 20

What is in the synapse?

Answer 20

Enzymes - for degradation which breaks down used neurotransmitters in the synapse

Question 21

When and which signal is picked up by a neuron depends on the…

Answer 21

1. Type of synapse and associated neurotransmitter (excitatory or inhibitory synapse)
2. Number of synapses and spatial position on the dendrites/soma of the input zone
3. Duration and synchrony of neurotransmitter release from different synapses

Question 22

What typical transmitters are at excitatory synapses?

Answer 22

Glutamate, aspartate, nicotinic acetylcholine (nACh), muscarinic Ach (slow EPSPs)

Question 23

What typical transmitters are at inhibitory synapses?

Answer 23

GABA, glycine, muscarinic acetylcholine

Question 24

What is temporal summation?

Answer 24

If the neurotransmitter is released for longer time into the synaptic cleft, then the postsynaptic potential is stronger

Question 25

What is spatial summation?

Answer 25

Is postsynaptic potentials arrive together in the integration zone, they are summed up

Question 26

What are spiking neurons?

Answer 26

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

Question 27

How is information coded in the neural networks?

Answer 27

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.**

Question 28

What are divergence neurons?

Answer 28

Divergence allows one neuron to communicate with many other neurons in a network.

Question 29

What are convergence neurons?

Answer 29

Convergence allows a neuron to receive input from many neurons in a network.

Question 30

What are deep neural networks?

Answer 30

DNNs have been shown to predict experimental outcomes (e.g. human perceptual similarity judgements, neural activity in primate sensory cortices)