Synapses & Action Potentials Flashcards
What are examples of neurotransmitters?
- Dopamine
- Serotonin
- Acetylcholine
- Substance P
- Glutamate
- GABA
- Histamine
- Endorphins
- Adrenaline
Depolarisation (at the post synaptic plasmalemma).
- More +ve ions cross into the neuron (making the inside more +ve)
- Excitatory postsynaptic potential (EPSP)
What does the distribution of Na+ and K+ lead to (in a neuron)?
An electrical gradient across the plasmalemma (greater +ve charge outside)
Hyperpolarisation (at the post synaptic plasmalemma).
Less +ve ions to cross into the neuron (inside more -ve)
Inhibitory postsynaptic potential (IPSP)
Excitatory postsynaptic potential (EPSP).
More +ve ions tocross into the neuron (making the inside more +ve)
– Depolarisation
Inhibitory postsynaptic potential (IPSP).
Less +ve ions to cross into the neuron (making theinside more-ve)
– Hyperpolarisation
Temporal Summation.
If lots ofExcitatory postsynaptic potentials (EPSPs) arriveone after the other in quick successionthis increases the neteffect
Spatial Summation.
MultipleExcitatory postsynaptic potentials (EPSPs) arriveat different locations on the dendriteincreases the net effect
When are action potentials able to occur?
If there’s enough Excitatory postsynaptic potentials (EPSPs)
- And outweighs the Inhibitory postsynaptic potentials (IPSPs) to give a net depolarisation
What does an increase in Ca++ lead to?
- Synaptic vesicles dock and fuse with axon terminal membrane
- The vesicles remain fused to the membrane until the Ca++ concentration has increased to a critical point
- At this point the vesicle fuses into the membrane and releases neurotransmitter into the synaptic cleft
- Retrieves new vesicles from a storage area so that the process can be repeated.
When an action potential arrives at an axon terminal/presynaptic process what happens?
Ca++ channels open
(so calcium floods into the bouton)
Relative refactory period
Immediately after peak K+ conductance as the Na+channelsbecome active and theplasmalemma repolarises.
- to set up an action potential requires more stimulus than when in the resting state
Absolute refactory period
Immediately after peakNa+ conductance theNa+ channels areinactive
- so noNa+ ions can move in or out and the hillock cannot fire another action potential
How do Na+ channels closing & K+ channels opening affect membrane potential?
Becomes more -ve
(no further Na+ enters the axon hillock and K+ exits the hillock)
What happens when a cell is hyperpolarised?
K+ channels to close and the cell then reverts to its resting potential
How does hyperpolarisation occur?
MoreK+ leaves the hillock than Na+ has entered so thepotential overshoots
What is the speed of propagation dependent on?
- Diameter of axon (larger = faster conduction)
- Presence of myelin (concentrates K+ and Na+ channels in nodes so increased conduction velocity)
Describe the unmasking of silent synapses.
- During recovery previously unused synapses are recruited
- Suggests the existence of structural synapses in the brain that are not normally functional due to competition
What is long-term potential (LTP)?
- Change in the performance or output of a synapse in the long term
- Related to increase in pre-synaptic neurotransmitter release + structural change of the post-synaptic structure
- Related to spatial + temporal summation (LTP occurs with high frequency stimulation or pairing of stimulation)
This is how we learn!
What is short-term potentiation?
- A change in the performance or output of a synapse in the short term
- An increase in synaptic strength due to increase in neurotransmitter production and/or altered post synaptic receptors
