Synapse 1 Flashcards
Functions of neurons:
Cell processes
Interconnect cells
Transmit information
Use electrical signals
What’s important to know about neurons?
Separate entities - separate cells that communicate with each other
What’s the only way that neurons can communicate with each other?
Through axons
Direction of signal in dendrites?
Propagates towards cell body
Direction of signal in axons?
Propagates away from cell body
Potential difference in axon before electrical activity generated?
-70 mV
Resting membrane potential
Characteristics of action potentials:
Self propagates
Travels in one direction - vectorial down axon
No ‘volume control’ - always same size of AP
What happens if there is a higher frequency of action potentials?
Faster signal
How are action potentials graded?
In frequency not amplitude
Where do action potentials start?
At cell body (axon hillock)
Where are action potentials transmitted in axons?
Towards end of axon - to end bulb/synapse
What do action potentials cause at the end of the axon?
Secretion of chemicals (neurotransmitters)
What essentially are neurons?
Elongated secretory cells that are polarised
How are neurons similar to secretory cells?
Axon is equivalent to apex of secretory cell
Dendrites are equivalent to basal aspect of secretory cell
What’s the axon end bulb the site of?
Chemical neurotransmitter release
What is the gap between two neurons called?
Synaptic cleft
WHat’s the cell before the gap called?
Presynaptic cell
What’s the cell called after the gap?
Postsynaptic cell
What does the swelling in terminal of presynaptic cell form?
Bouton
What is reception of signals by?
Via highly branched processes - dendrite tree and dendritic spines
How does vesicle and presynaptic membrane recognise each other?
v-SNARE on vesicle complexes with t-SNARE at presynaptic membrane
What do v-SNARE and t-SNARE do?
They form a complex that folds strongly to draw vesicle and presynaptic membranes close
What happens when vesicle and presynaptic membranes are drawn close?
Vesicle is docked on membrane - clamped by synaptotagmin
What removes vesicle from synaptotagmin clamp?
Action potential triggers calcium influx at end-bulb
This reorient membrane and helps align SNARE complex for fusion
Where are peptide neurotransmitters made?
RER
Packaged into vesicles in Golgi
What happens after peptide neurotransmitters leave Golgi?
Transported along microtubules to axon terminal
Vesicles are then charged in axon terminal
What are the two classes of receptors for neurotransmitters on post synaptic membrane?
Ionotropic receptors - fast signals
Metabotropic - slow signals
How do ionotropic receptors work?
Neurotransmitter binds to receptor - induces conformational change
Pore opens + ions flow in/out
Voltage of cell then changes
What can ionotropic receptors do to voltage of cell?
Decrease potential = negative ions out or positive ions in
Increase potential = negative ions in or positive ions out
Give an example of ionotropic receptor:
Acetylcholine receptor
Give an example of metabotropic receptor:
G protein-linked receptor
What happens in metabotropic receptors?
Receptor binds G-protein (GTP replaces GDP)
Active G-protein then leaves + binds target enzyme
Enzyme generates messenger
Messenger binds channel + channel opens
What happens after metabotropic receptor causes ion channel to open?
GDP-ase removes P from GTP which then inactivated G protein
G protein then leaves enzyme - inactivated enzyme
G protein is then free + ready to bind to receptor
Summary of how an ionotropic receptor works:
Neurotransmitter binds
Channel opens
Ions flow across membrane
Summary of how metabotropic receptors work:
Neurotransmitter binds
G-protein is activated
G-protein subunits or intracellular messengers modulate ion channels
Ions flow across membrane
Ion channel opens
What have electrophysiological experiments shown?
That the release of neurotransmitters is quantal - in packets
What does quanta relate to?
The release of contents of single vesicles at the presynaptic membrane
What results in a stronger signal at the post synaptic membrane?
More vesicles released
What are PSPs caused by?
The passage of ions through ion channels which have opened following receptor/neurotransmitter interactions
What does PSP stand for?
Post synaptic potential
What is an excitatory PSP (EPSP)?
A net flow of positive ions into the cell
Causes depolarisation of membrane - brings closer to threshold
Single ESPs:
Rarely result in action potential
Amplitude in inhibitory and excitatory PSPs:
Amplitude of signal decreases with distance and time
What’s the typical amplitude of an EPSP?
Positive deflection (depolarisation) of between 1-5mV
What’s the typical amplitude of an IPSP?
Negative deflection (hyperpolarisation) of between 1-5 mV
What’s spatial summation?
Multiple end-bulbs on same dendrite
Make large change in potential
What’s temporal summation?
One axon firing very quickly
Recovery is slow
Difference between single EPSP and summed SPSPs:
Single = potential difference may not reach threshold
Summed = threshold reached and AP generated
What’s hyperpolarisation caused by?
Inhibitory PSP
IPSP
What can APSPs be caused by?
Direct (ionotropic) or indirect (metabotropic) gating
