Synapses and role of neurotransmitters Wk2 Flashcards
1
Q
What are neuronal specialisations for communication?
A
- Dendrites: input from other neurones
- Axons: Impulse conduction
- Axon terminal/synaptic bouton: release of neurotransmitter
2
Q
What is an electrical synapse?
A
- “Gap junction”
- Fastest and most primitive
- Between adjacent cells or neurites
- Direct transfer of ionic current (also small molecules)
- Bi-directional
- Allows synchronous activity between cells
- Relatively rare between neurones in CNS but important in development
3
Q
Where are synapses located?
A
- Glia-neuron
- Glia-glia communication
- Cardiac myocytes
4
Q
What is a connexon?
A
- Made of 6 connexins
- Physical bridge lined up between membranes
5
Q
What is a chemical synapse?
A
- Close association between presynaptic (axon terminal) and postsynaptic membrane
- Presynaptic terminal releases neurotransmitter
- Diffuse across the synaptic cleft
- Postsynaptic dendrite is synaptic contact with a dentric tree
- Interacts with receptor on postsynaptic membrane
6
Q
Process of synapse
A
- Na+ channels open and action potential invades nerve terminal causing depolarisation
- Depolarisation triggers Ca2+ channel opening causing Ca2+ influx
- Neurotransmitter releases by exocytosis (Ca2+ dependent) - contents go vesicle exposed to extracellular space and they move by simple diffusion across
- Diffusion across the synapse and receptor binds with post synaptic receptor
- Post synaptic effect occurs - short and sharp
- Rapid termination of signal by reuptake of neurotransmitter to enzymatic breakdown; reuptake of neurotransmitter by proteins (enzymatic breakdown); signal is terminated by presence of enzymatic activity around synapse-enzymatic breakdown
7
Q
Name different major neurotransmitters
A
- Major excitatory: amino acids: glutamate
- Major inhibitory: y-aminobutyric acid (GABA)
- Glycine
- Acetylcholine
- Monoamines: Noradrenaline, dopamine, 5-hydroxytryptamine (5-HT; seratonin)
- Neuroactive peptides (>100 different kinds)
8
Q
What are neurotransmitter receptors?
A
- Membrane spanning protein molecules
- Transmitter binding causes structural/conformational change = signal)
- Receptors are specific for a neurotransmitter (exclusive relationship but not vice versa)
- One neurotransmitter = several receptor subtypes
9
Q
What is an ionotropic receptor signalling mechanism?
A
- (moving of ions)
- Receptor operated/ligand gated channels
- Transmitter binding ==> Conformational change in protein ==> Channel opening in pore ==> Ion movement into channel
10
Q
What is an metabotropic receptor signalling mechanism?
A
- G protein coupled
- Much slower but potentially longer lived and associated with receptor protein
- Transmitter binding ==> Conformational change ==> Activates G-protein ==> Activates ‘effector systems’ ==> Indirect effects e.g. open or close ion channels, stimulate or inhibit enzymes/secondary messenger systems
11
Q
What is an excitatory inotropic receptor?
A
E.g. glutmate AMPA, NMDA, kaintate receptor sub, ACH nicotinic receptor
- Small increase in membrane potential (bump)
- Small excitatory post synaptic potential = EPSP
12
Q
What happens in inhibitory synapses?
A
- Chloride ion moves in - goes against negative charge (hyperpolarisation)
- Small decrease in membrane potential (upside down bump)
- Small inhibitory post synaptic potential (IPSP)
13
Q
What are metabotropic (G-protein coupled) receptor?
A
- Open or close ion channels
- Stimulate or inhibit enzymes/secondary messenger systems
- E.g. Ach muscarinic, GABAb, monoamine receptors (except 5-HT3)
14
Q
What is spatial summation?
A
- Summing of post synaptic potentials generated at separate synapses
- Occurs when more Na+ is coming in than leaving so action potential is generated
15
Q
Excitatory + inhibitory (spatial summation) =
A
No change
