Term
| Name and explain the 3 types of synaptic connections in the CNS |
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Definition
axo-dendritic (axon synapses with a dendrite - classic)
axo-somatic (axon synapses with the soma/cell body)
axo-axonic (axon terminals synapses with another axon) |
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Term
| Name two other less common connections |
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Definition
soma-somatic
dendro-denritic |
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Term
| Describe an axo-dendritic connection |
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Definition
can occur on dendritic spines or directly on the dendritic shaft
commonly excitatory (e.g. glutamate) |
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Term
| Where are dendritic spines common? |
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Definition
| on the dendrites of the principle cells of most brain regions (e.g. pyramidal cells in cerebral cortex) |
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Term
| How do dendrites change in presence/absence of stimulus? |
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Definition
| when exposed to a lot of excitatory NT it will grow in structures, however, when the stimulus is removed, spines retract if not needed. |
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Term
| Describe an axo-somatic connection |
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Definition
inhibitory (e.g. GABAergic)
synapses on axon hillock will influence cell firing greatly |
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Term
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Definition
| this is where voltage gated Na+ channels are concentrated |
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Term
| Give an example of an axo-somatic connection |
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Definition
| cerebellar basket cells have lots of axonal collaterals that go to many Purkinje neurones and wrap around the cell bodies |
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Term
| Describe an axo-axonic connection |
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Definition
- modulatory and control transmitter release
- can increase or decrease NT release
- control ca2+ influx in the pre-synaptic neurones |
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Term
| Describe the mechanism of presynaptic facilitation that increases NT release (with diagram) |
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Definition
1) excitatory presynaptic (C) terminal depresses the potassium current in the terminal (A)
2) calcium current in the terminal of A is therefore increased
3) there is an increase in transmitter release between A and B
4) amplitude of the synaptic potential in the postsynaptic neurones (B) is increased |
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Term
| Describe the mechanism of presynaptic inhibition that decreases NT release (with diagram) |
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Definition
1) presynaptic inhibitory terminal (C) depresses the calcium current in the terminal (A)
2) reduction in the amount released between A and B
3) the synaptic potential recorded in B is reduced |
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Term
| Describe the direction of flow of neuronal information |
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Definition
1) the AP propagates along the axon from the axon hillock
2) NT is released from the presynaptic axon terminal and causes a synaptic potential in the postsynaptic cell
3) synaptic potential travel along dendrites towards the cell body where they are integrated |
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Term
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Definition
| many neurones communicate with a given neurone |
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Term
| How do neurones receive information? |
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Definition
| in the form of EPSPs or IPSPs and integrate it and then generate an AP or not |
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Term
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Definition
| neurones communicate with many other neurones, by having an axon with many branches (axon collaterals) |
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Term
| Describe neural integration |
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Definition
| summation of EPSPs and IPSPs at axon hillock. AP is triggered if membrane potential at the axon hillock is depolarised to threshold |
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Term
| Define and draw temporal summation |
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Definition
| summation of PSPs occurring over short period of time |
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Term
| Define and draw spatial summation |
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Definition
| summation of PSPs over membrane surface |
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Term
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Definition
| Excitatory post-synaptic potential (EPSP): a graded depolarisation caused by the arrival of neurotransmitter at the postsynaptic membrane. |
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Term
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Definition
| Inhibitory post-synaptic potential (IPSP): a graded hyperpolarisation of the postsynaptic membrane. |
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Term
| Describe frequency coding |
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Definition
- Action potentials are an all-or-nothing phenomenon, and therefore not much information can be carried in their signal.
- However, the frequency of action potentials can influence the amount of neurotransmitter released at a synapse.
- When action potentials occur at a high frequency, more neurotransmitter is released from the neurone.
- Therefore, higher frequency of action potentials corresponds to stronger communication between neurones. |
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Term
| What does a larger depolarisation mean regarding APs? |
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Definition
| A larger depolarisation doesn’t mean a bigger action potential; it just means a greater frequency of action potentials. The action potential will happen regardless of whether the membrane has only just reached threshold potential or whether it has exceeded it say, 10-fold. |
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Term
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Definition
self-propagating wave of depolarisation
1) influx of Na+ bring neighbouring region to threshold
2) regenerative depolarisation along the axon
3) depolarisation occurs left and right but AP only one direction |
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Term
| Define orthodromic direction |
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Definition
| normal direction of AP propagation (hillock to terminal) |
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