Neurotransmitters & synapses Flashcards
How are neurotransmitters packaged into vesicles?
- enzymes that are needed to make small molecule transmitters are synthesized in the cell body and move to presynaptic terminal
- substrates transported to pre synaptic terminal
- transported into vesicles
- large neuropeptide precursors are synthesised in the cell body packaged into vesicles & transported along microtubule
How are neurotransmitters released?
- small vesicles docked near ca2+ channels
- AP invades terminal
- Ca2+ channels open & Ca2+ enters
- vesicles fuse with presynaptic membrane and release contents
- vesicle membrane recycled
Describe neurotransmission
- AP arrives at nerve terminal which opens Ca2+ channels
- Ca2+ entry causes vesicle fusion and transmitter release
- receptor channels open, transmitter binds to receptor and causes Na2+ ion channel to open
- Na2+ enters the postsynaptic cell and vesicles recycle
what is an axosomatic synapse?
synapse between the axon of one neuron and the body of another
what is a axodendritic synapse?
- synapse between dendrite of one cell and a dendrite of another
what is a axo-axonic synapse?
- type of synapse, formed by one neuron projecting its axon terminals onto another neuron’s axon
What is a mixed cation ion channel?
- channel that for example lets Na+ enter and K+ leave
what is an excitatory postsynaptic potential? EPSP
- Postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential
- temporary depolarization of the postsynaptic membrane
Compare EPSP vs IPSP
- excitatory (EPSP) = depolarization of postsynaptic cell - sufficient depolarisation could produce AP, eg glutamate in CNS binding to AMPA receptors
- Inhibitory (IPSP) = hyperpolarisation or repolarisation of postsynaptic cell , prevents action potential, eg GABA binding to receptors
whats the difference between GABA a and GABA b?
- IPSP, due to Cl- entering the cell (GABA a type) or K+ ions leaving the cell (GABA b type)
what happens if EPSP’s summate (adding up together) ?
- EPSP’s can summate to cause the cell to depolarise sufficiently to allow the cell to fire an action potential
- causes the cell to communicate with the next nueron
compare and contrast spatial summation vs temporal summation
- Spatial - input to different dendrites
- Temporal - repetitive input onto the same terminal in a dendrite
what are the important steps for transmission at a chemical synapse?
- neurotransmitter synthesis either in presynaptic terminal or in the neuronal cell body
- concentration and packaging of neurotransmitter molecules in preparation for release
- release of neurotransmitter into synaptic cleft
- Binding of neurotransmitter by post synaptic receptor molecules
- termination of neurotransmitter action preparing the synapse for subsequent (coming after something in time , following ) release of neurotransmitter
what is the priming stage of neurotransmitter recycling?
- vesicles in the reserve pool undergo priming to enter readily reversible pool
- involves assembly of SNARE complexes
What are snare proteins and what is their function?
- large protein family
- they mediate vesicle fusion - the fusion of vesicles with target membrane or membrane bound compartments
- examples : synaptotagmin & synaptobrevin
what is the function of synaptotagmin?
- functions as a calcium sensor
- entering Ca2+ binds to synaptotagmin and Ca2+ bound synaptotagmin catalyses membrane fusion
what are the two types of postsynaptic receptors?
- Ionotropic
- Metabotropic -
What is the difference between ionotropic and metabotropic receptors?
- they are both ligand gated transmembrane proteins
- ionotropic receptors change shape when they are bound to a ligand - channels open and ions flow in eg nAchR
- metabotropic receptors do not have a channel that opens or closes, instead they are linked to a ‘ G protein’, ligand binds to receptor which activates G protein which activates a secondary messenger
what is a secondary messenger?
- A secondary messenger is a chemical whose function is to go and activate other particles
How is a neurotransmitter removed after release?
- uptake by glial cells
- enzymatic degradation eg acetylcholinesterase
- internalization by postsynaptic process
explain the pathway steps of neurotransmitters
what is an example of a fast ionotropic receptor?
- Nicotinic Ach receptors
- pentameric receptor - 5 subunits
- Ach binds to the 2 alpha subunits which causes conformational change which ooens ion channel
what are the 2 ionotropic glutamate receptors?
- AMPA
- NMDA
- excitatory throughout CNS
what is LTP induction?
- long term potentiation
- induction of the NMDA receptor is a chemical synapse in the brain - substantial rise in calcium ion conc in postsynaptic cell
what are the main inhibitory neurotransmitters?
- Glycine - mainly spinal chord ( activates Cl- channels)
- GABA released by many inhibitory CNS inter neurons
- GABA a - receptor activation opens Cl- channels ( Cl- enters and causes hyperpolarisation)
- GABA b -metabotropic receptor opens K+ channels - K+ exits cell and causes hyperpolarisation
what are neuropeptides?
- chemical messengers made up of small chains of amino acids that are synthesized and released by neurons
