Synaptic transmission and neural integration Flashcards
What is synaptic transmission
A typically fast process of transferring information between neurons or between neurons and muscle fibres.
Synaptic transmission occurs between neurons through either what two things
Chemical synapses or electrical synapses
What is the ionic mechanism of End-plate potentials
Transient opening of ion channels permeable to both Na+ and K_
End-plate potential is always supathreshold, what does this mean?
Once triggered, AP is transmitted along the muscle fibres
What are the three key features of a chemical synapse
Specifity, complexity and plasticity
a key feature of a chemical synapse
What is specificity?
Special neurotransmitters have specific effects on postsynaptic membrane.
a key feature of a chemical synapse
What is complexity?
Type, time, course, strength, location and timing etc
a key feature of a chemical synapse
What is plasticity
Changes in synaptic structure and function associated with development, aging, learning etc.
What are the two main types of chemical synapses in the CNS
Excitatory and inhibitory
Why do we need chemical synapses
- At a chemical synapses, depolarisation at the presynaptic terminal causes the release of a neurotransmitter which diffuses across the synaptic cleft and binds to receptors in the postsynaptic membrane.
- The binding usually initiates an opening of a channel associated with the receptor, and a current in the postsynaptic cell.
What are excitatory synapses
Depolarisation of the postsynaptic membrane called the Excitatory Postsynaptic Potential (EPSP)
What are inhibitory synapses
Hyperpolarisation of the postsynaptic membrane called the Inhibitory Postsynaptic Potential (IPSP)
What are the main neurotransmitters involved in the production of EPSPs
Glutamic acid and acetylcholine.
What is the ionic mechanism of EPSPs
The opening of channels selective for Na+, K+ and sometimes Ca2+.
What are the main neurotransmitters involved in the production of IPSPs
Mainly gamma-aminobytyric acid (GABA) or glucine.
Wh
What is the ionic mechanisms of IPSPs
Often through the opening of K+ channels which hyperpolarises the cell membrane (moves RMP away from threshold)
What are the two types of mechanisms used to gate ion channels by neurotransmitters.
Direct gating and indirect gating
What is direct gating
Where the transmitter binds to the receptor/ion channel complex, causing the pore to open and ions to pass through, depolarising and hyperpolarising the cell membrane.
What is indirect gating
Where the transmitter binds to receptors (such as G-protein-coupled), also known as metabotropic receptors) activating the biochemical pathway which involves a G-protien.
Role of G proteins in indirect gating
G-proteins are membrane-enclosed proteins which bind GPT when activated by membrane receptor. This leads to the production of second messengers such as cAMP.
Protein kinases activated by the second messenger phosphorylate specific ion channels, causing them to open or close and thus, the membrane potential changes.
Is direct or indirect gating faster/longer lasting
Direct gating is faster on oniset and short-lasting.
Indirect gating effects are slower in onset and longer-lasting
What are the two classifications of neurotransmitters
Small molecule neurotransmitters (classical neurotransmitters) and neuropeptides (neuromodulators)
What are classical neurotransmitters
Usually fast and often act indirectly on postsynaptic receptors.
What classifies under classical neutrotransmitters
- amino acids (glutamate, GABA, glycine)
- Acetylcholine
- Biogenic amines (dopamine, norepinephrine, serotonin 5-HT)
What are neuropeptides
Large molecule chemicals with indirect (metabotropic) action, or modulatory action on the effects of other neurotransmitters. They tend to exert slow and usually a more diffuse action.
There are dozens of neuropeptides identified to be involved in the communication between neurons, what are some examples?
- enkephalin
- substance P
- Neuropeptide Y (NPY)
What are the factors determining synaptic action
- type of neurotransmitter/neuromodulator
- type of neurotransmitter receptor/channel complex expressed in the postsynaptic membrane
- amount of neurotransmitter receptor present in the postsynaptic membrane - synaptic plasticity: long term potentiation (LTP) or long term depression (LTD)
What are the three ways to cause neurotransmitter inactivation (and recovery)
- diffusion away from synapse
- enzymatic degradation in the synaptic cleft
- reuptake for most of the aminoacids and amines and recycling.
What is excitotoxicity
- increased release of neurotransmitters
- example: glutamate
- leads to increases Ca2+ accumulation
- activates enzymes that kills the cell
