Pre synaptic events Flashcards
what are neuronic connections picked up by?
dendrites
what are the three types of synapses?
- axo dendritic
- axo somatic
- axo axonic
what is axo dendritic?
Single synapse onto dendrite
what is axo somatic?
Synapse onto the cell body
Common with inhibitory
Regulating the ability of the cell body to fire an action potential
what is axo axonic?
Onto an axon
Regulating the firing of one neuron to another
what is found in the presynaptic nerve terminal?
presynaptic vesicles
mitochondira
how are presynaptic vesicles ordered in the pre synaptic nerve terminal?
- clustered by the synaptic membrane
- Called the active zone
- Where vesicles are docking and releasing their neurotransmitters
- Active zone is directly opposite the post synapse
what are dark patches?
- density of proteins
- on both sides of the synapses
- tether the vesicles and form a mesh
why does the active nerve terminal need lots of mitochodnria?
need ATP for active transporter
what is contained in the pre synatpic vesicles?
neurotransmitters
what are the main neurotransmiiters in the brain?
GABA
Glutamate
what is GABA?
major inhibitory neurotransmitter
30 - 40% of synapses
what is Glutamate?
major excitatory neurotransmitter
>50% synapses
what is meant by a fast receptor type?
ligand gated ion channel
what is meant by a slow receptor type?
G protein coupled metabotropic receptor
what are the steps involved in pre synaptic transmission?
- action potential down axon, causes an influx of Ca2+
- Ca2+ conc causes vesicles to fuse with the membrane
- released NT diffuses across the synaptic cleft
- NT activates pre synaptic ‘auto receptors’
- NT can ‘spill’ into adjacent synapses
- NT degraded or taken up by glia or pre synaptic transporters
describe what happens when an action potential travels down the axon in pre synaptic transmission.
- there is a massive concentration of Ca2+ ion channels
- action potentials causes depolarization which opens the voltage gated Ca2+ ion channels
- influx of ca2+
describe what happens when there is an increase of Ca2+ in the pre synaptic terminal in pre synaptic transmission.
- Ca2+ increase causes the synaptic vesicle to fuse with the plasma membrane
- the vesicle releases its contents in the the synaptic cleft
describe what happens when NT diffuses across the synaptic cleft in pre synaptic transmission.
- Interacts with specific neurotransmitter receptors
- Synaptic cleft width ̴50nm (really narrow)
- Pre and post are connected across the gap by chains of proteins, they are hooked up together
what is the role of auto receptors?
feedback and regulate
describe an experiment to prove the involvement of Ca2+ using a giant squid axon
- Stick an electrode into the presynaptic nerve terminal (recording)
- Electrode into the axon (stimulating)
- Electrode into the post synaptic (recording)
- Put in drugs to isolate currents
- Inject current to stimulate an action potential
- Ca2+ into nerve terminal
- Have pore forming subunits
- S4 helix ( important for voltage sensing)
what drugs could you use in order to only study Ca2+ channels?
- Inject current to stimulate an action potential
- Ca2+ into nerve terminal
what is the S4 helix?
- twists to open the channel
- resting Ca2+ conc is low inside but high outside
- release sites clustered around Ca2+ channels
how did Katz show quantal release using the skeletal nerve muscle synapse?
- stimulate the axon and record the post synaptic membrane potential
- little stimulations not above the threshold
explain how to stimulate and record the post synaptic membrane potential in Katz’s experiment.
- Intracellular microelectrode records membrane potential
- Action potential in pre synaptic motor neuron elicits a depolarisation in the post synaptic muscle fibre
- called an end plate potential (EPP)
- bring the membrane potential above the threshold for producing an action potential
- causes contraction
explain the presence of little stimulations that are not above the threshold in Katz’s experiment
- occur in the absence of a stimulus
- little blips (mini EPPs)
- corresponds to a synaptic vesicle
- little blips are the snaptic vesicle spontaneously fusing with membrane and releasing their contents
- upped the voltage and could release 1,2 or 3 of the vesicles
- called it quantal release
what does a synaptic vesicle have on its surface?
lots of proteins
what are the main features of synpatic vesicle?
- born from budding off an endosome
- NT transporter
- translocate to the mebrane
- docking
- primary profusion
- exocytosis
- brings vesicle back in - endocytosis
what is synpatotagmin?
Ca2+ sensor
what problem needs to be overcome in fusion?
- membranes contain phospholipids which repel each other
- need lots of energy to overcome this
what is needed for fusion?
SNARE proteins
how can fluorescent antibodies be used for labelling?
Bind to the membrane domain of the protein
how can fluorescent dyes be used for labelling?
- Put dye on neurons and stimulate
- Takes up the dyes
- Amphipathic dyes that fluoresce when bound to membranes
how can fluorescent proteins be used for labelling?
- pH sensitive fluorescent proteins
- pH 7 outside
- pH 5 inside the vesicle
what do SNARE proteins do?
- found at the vesicle and plasma membrane
- Bind and form an energetically complementary complex
- Brings membranes together
