Lecture 8: Presynaptic Processes Flashcards
What are neurotransmitters? What are they released into?
chemical signals released from presynaptic nerve terminals into the synaptic cleft
How is a signal passed on from one neuron to the next?
release of one (or more) chemicals from the axon terminal -> these chemicals act on receptors of the target cell to temporarily change the properties of that cell i.e. change in membrane potential or conductance
What are the criteria that must be met in order for a chemical to be considered a neurotransmitter?
synthesis: must be produced within a neuron
storage: must be found within a neuron
release: must be released when the neuron is depolarised
receptor: must act on a post-synaptic receptor and cause a biological effect
inactivation: there must be a mechanism for inactivation (uptake / degradation)
if applied on a post-synaptic membrane, it should have the same effect as when released by a neuron
What are examples of classical (small molecule) neurotransmitters?
amino acids such as glutamate, GABA and glycine
monoamines such as noradrenaline, dopamine, adrenaline and serotonin
acetylcholine
What are examples of non-classical (large peptide) neurotransmitters?
peptides such as substance P, somatostatin, enkephalin and kisspeptin
gases such as nitric oxide and carbon monoxide
lipids such as anandamide
How are classical and non-classical neurotransmitters synthesised?
classical: uptake or enzymes
non-classical: protein synthesis
How long is the duration of action for classical and non-classical neurotransmitters?
classical: fast and short
non-classical: slow and long
What are the vesicles like for classical and non-classical neurotransmitters?
classical: small (filled by transporters)
non-classical: large (secreted proteins from RER)
What is the sequence of events involved in neurotransmission?
NT synthesised and stored -> AP -> depolarisation and opening of VGCC -> Ca2+ influx -> vesicles fuse with presynaptic membrane -> NT released via exocytosis -> NT binds receptors on postsynaptic membrane -> postsynaptic channels open -> postsynaptic current causes EPSP or IPSP -> reuptake and / or breakdown of NT
What do VGCCs couple?
couple membrane depolarisation to NT release
Ca2+ that enters binds to release proteins to cause vesicle fusion
What are the different types of VGCCs?
N-type (Cav2.2) - classical blocker: conotoxin (cone snails)
P/Q (Cav2.1) - classic toxin agatoxin (spiders)
How are neurotransmitters released and what is this known as?
NTs are released in packets and this is known as quantal release
Neurotransmitters are released in packets. What does this determine?
determines the minimum size of a postsynaptic potential (EPSP or IPSP in neurons)
What is an mEPP?
the change in the membrane potential of a muscle cell produced by a single quantum is called a miniature end-plate potential
What is a quantum?
the amount of neurotransmitter in 1 vesicle