chemical synaptic transmission SEM1 Flashcards
what is the criteria that define a neurotransmitter
A)Presence at Synapse: Must exist in the synapse with pathways for its synthesis.
B)Calcium-Dependent Release: Released upon stimulation (like a pre-synaptic action potential) through a mechanism dependent on calcium ions.
C)Specific Receptors: Must have specific receptors on the post-synaptic cell
what is end plate potential (EPP)
the conversion of an electrical signal in the nerve into a mechanical response in the muscle resulting in muscle contraction
what do NMJ function with
high safety factor
what does the safety factor at the NMJ ensure
ensures the end plate potentials (EPPs) are much larger than required for reliable muscle action potential generation
what is the normal response of calcium entering a neuron
action potential triggers chain reaction => calcium enters neuron => promotes release of acetylcholine => imitating muscle contraction
what occurs if tetrodotoxin blocks the initial action potentials in neuron
chain reaction leading to calcium entering neuron is halted preventing muscle contraction
what are the 4 main steps of calcium induced vesicle fusion and neurotransmitter exocytosis at a synapse
1)vesicle docks
2)SNARE complex formation
3)calcium entry
4)membrane fusion and neurotransmitter release
what occurs during vesicle docking during Ca2+ induced vesicle fusion
neurotransmitter vesicles attach to presynaptic membrane with SNARE proteins (e.g syntaxin and SNAP-25)
what occurs during SNARE complex formation during Ca2+ induced vesicle fusion
SNARE proteins tightly bind together pulling the vesicle and presynaptic membrane close for fusion
what occurs during calcium entry during Ca2+ induced vesicle fusion
voltage-gated calcium channels open due to incoming action potential, allows Ca2+ ions to enter and bind to synaptotagmin on vesicle
what occurs during membrane fusion and neurotransmitter release during Ca2+ induced vesicle fusion
calcium-bound synaptotagmin triggers fusion of vesicle w/ presynaptic membrane => release of neurotransmitters into synaptic cleft to signal next neuron
what is the function of SNARE proteins
mediate the fusion of vesicles containing neurotransmitters, hormones etc w cell membranes to release their contents
what is the process of vesicular exocytosis and recycling at a synaptic terminal
1)brief stimulation of presynaptic terminal
2)washing away extracellular HRP
3)formation of clathrin-coated pits
4)recycling and reformation of synaptic vesicle
5)continuous cycle of endo and exocytosis
At the NMJ what does acetylcholine bind to
Binds to post-synaptic nicotinic acetylcholine receptors (nAChR)
What are nicotinic acetylcholine receptors (nAChR)
nAChR are ligand-gated ion channels
How is acetylcholine cleared from the synaptic cleft
By the enzyme acetylcholinesterase
What does the enzyme acetylcholinesterase do
Hydrolyses acetylcholine to choline and acetate
What are combined together to synthesise acetylcholine
Acetyl CoA and choline are combined by the enzyme choline acetyltransferase (ChAT)
What are the two types of synaptic communication
Electrical and chemical synapse
what is Dale’s law
the same neuron uses the same set of neurotransmitters at all of its synapses
what occurs at the axon hillock
low threshold action potentials originate here
What is the process of synthesis and release of glutamate in the brain
1)synthesis of glutamate
2)storage and release
3)reuptake and recycling
4)modulation
What is L-glutamate
Major ‘fast’ excitatory neurotransmitter in the mammalian CNS
What is glutamate
Amino acid
How is glutamate synthesised
Synthesised from glutamine (Gln) by the enzyme-phosphate-activated glutaminase (PAG) in the presynaptic neuron
Where is glutamate stored and released
Stored in the synaptic vesicle within the presynaptic neuron and released into the synaptic cleft
What can glutamate do once released
Bind to receptors on the postsynaptic neuron to propagate the neural signal
How is glutamate recycled
Excess glutamate taken up by neurons and glial cells through plasma membrane transporters to be recycled or broken down
What are ionotropic glutamate receptors (iGluRs)
Membrane ion channels that are gated by glutamate
What are metabotropic glutamate receptors (mGluRs)
Seven transmembrane domain proteins that couple to G proteins
What are gamma amino-butyric acid (GABA) and glycine
Inhibitory amino acid neurotransmitters
What do GABA and glycine mediate
Mediate fast synaptic inhibition through activation of ionotropic receptors
How is GABA synthesised
GABA synthesised in the presynaptic neuron from glutamate by the enzyme glutamic acid decarboxylase (GAD)
Where is is GABA stored and released
Stored in synaptic veiscle within presynaptic terminal and released into synaptic cleft
What is the action of GABA at the postsynaptic receptor
Binds to GABA receptors on postsynaptic neuron and leads to opening of ion channels resulting in hyperpolarisation of the neuron => inhibiting neuronal activity
What is the process of the reuptake of GABA
Removed by reuptake into neurons and glial cells via GABA transporters (GAT) - reuptake terminates inhibitory signal
How is GABA broken down/recycled
Broken down by enzymes or recycled back into glutamate
What usualy causes an increased influx which causes hyperpolarisation inside a neuron
Typically increased influx of chloride ions
What are properties of glycine receptors
Ionotropic
Conduct CL- ions
What are properties of GABAa receptors
Ionotropic
Conduct Cl- ions
What are properties of GABAb receptors
Metabotropic
Coupled to G-proteins
