Synaptic integration and plasticity

Question 1

Whats signal transduction?

Answer 1

Changed in ionic gradient/ membrane potential such as action potentials have to be transduced in order to produce physiological actions

Question 2

Whats a classic example of signal transduction?

Answer 2

Synaptic transmission

Question 3

Transduction of voltage changes to biochemical changes result in what?

Answer 3

Synaptic release

Excitation-contraction coupling

Question 4

What are the steps to quantal synaptic transmission?

Answer 4

1. Transmitter is synthesised and then stored in vesicles
2. An AP invades the presynaptic terminal
3. Depolarisation of presynaptic terminal causes opening of Voltage-gated Ca2+ channels
4. Influx of Ca2+ through channels
5. Ca2+ causes vesicles to fuse with presynaptic membrane
6. Transmitter is released into synaptic cleft via exocytosis
7. Transmitter binds to receptor molecules in postsynaptic membrane
8. Opening or closing of postsynaptic channels
9. postsynaptic current causes excitatory or inhibitory postsynaptic potential that changes the excitability of the postsynaptic cell
10. Retrieval of vesicular membrane from plasma membrane

Question 5

Whats quantal synaptic release?

Answer 5

Quantal release is the mechanism by which most traditional endogenous neurotransmitters are transmitted throughout the body

Question 6

Tell me about transmission and neuromusuclar junction- nmj/ quantal release ACh

Answer 6

• 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

Question 7

What are end plate potentials (EPPs)?

Answer 7

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

Question 8

What are the functional properties and synaptic ‘chemical’ transmission?

Answer 8

• 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

Question 9

In order for information to pass from one neuron to the next, what must happen?

Answer 9

• The information must cross both the pre- and post- synaptic membranes
• The AP signals in the axon must be transduced into release of neurotransmitter

Question 10

What is the size of the post-synaptic response related to?

Answer 10

The number and timing of pre-synaptic APs- intensity coding

Question 11

Diagrammatic outlin of cell-to-cell information transfer within the nervous system

Answer 11

Question 12

Name an inhibitory and excitatory synapse?

Answer 12

Inhibitory: GABA/glycine

Excitatory: Glutamatergic

Question 13

Excitatory and inhibitory synapses, what do each of these have a flux of?

Are they symmetric or asymmetric

Answer 13

Glutamatergic= excitatory= flux of Na+/Ca2+ ions

GABA/ glycine= inhibitory= flux of Cl-

Question 14

What do glutamate receptors produce?

Answer 14

Question 15

What do GABA receptors produce?

Answer 15

Question 16

Answer 16

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)

Question 17

Why is there integration of synaptic potentials?

Answer 17

• 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

Question 18

A synaptically induced potential can increase and decrease what?

Answer 18

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

Question 19

What factors are involved with Neurocomputation (synaptic potential to AP conversion)?

Answer 19

• 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

Question 20

What are temporal summation of EPSPs?

Answer 20

Successive synaptic inputs that occur before the neurone has had time to fully recover can sum together to produce a greater overall effect

Question 21

Whats spatial summation?

Answer 21

Multiple inputs into one neuron

Multiple synaptic inputs on to different parts of the neurone can sum together to produce a greater overall effect

Question 22

What do temporal and spatial summation produce?

Answer 22

Graded post-synaptic depolarisations

Question 23

What do greater post-synaptic depolarisations produce?

Answer 23

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

Question 24

Whats meant by Convergence of a neuronal pathway?

Answer 24

Neuronal pathways may lead to signals from multiple neurones converging onto a single target neurone - CONVERGENCE

Question 25

Whats meant by divergence of a neural pathway?

Answer 25

Neuronal pathways carrying signals from a single neurone being sent onto multiple neurones - DIVERGENCE

Question 26

Give an example of convergence in neuronal pathways?

Answer 26

e.g. convergence in retina

Rods = high convergence = low acuity

Cones = low convergence = high acuity

Question 27

Give an example of divergence in a neuronal pathway?

Answer 27

e.g. divergence- crossed extensor reflex

Also, one α-motor neuron to multiple muscle fibres

Question 28

Give an example of two things that synaptic plasticity can lead to?

Answer 28

1. Long-term potentiation LTP
2. Long- term depression LTD

Question 29

Tell me about long-term potentiation?

Answer 29

• 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

Question 30

Tell me about long-term depression?

Answer 30

• 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

Question 31

Whats quantal release?

Answer 31

basically, the idea that the neurotransmitters are released in discrete quantities