Lecture 8 - Synaptic Transmission II Flashcards
True or False?:
Acetylcholine is broken down in the neuromuscular junction into acetate and choline. Choline is then recycled back into the presynaptic cell.
True
What happens to an ionotropic receptor if its associated transmitter is not removed quickly and the channel stays open for a long time?
It will go to the desensitized state. It will be shut and stay shut until it is reset into the resting state.
How do astrocytes respond to synaptic activity?
Astrocytes respond to synaptic activity through an increase in intracellular calcium.
How do you stop synaptic transmission?
The transmitter must be (rapidly) removed from the synaptic cleft.
True or False?:
Cholinergic receptors have a very negative reversal potential.
False
Cholinergic receptors have a reversal potential around zero.
How is glutamate removed from the synaptic cleft and recycled?
Glutamate is pumped out of the synaptic cleft by the excitatory amino-acid transporters (EAAT) on the neighbouring astrocyte (part of the tripartite synapse). To avoid resignaling while transferring the recycled glutamate from the astrocyte to the presynaptic cell, the astrocyte turns glutamate into glutamine. The glutamine is then taken back into the presynaptic cell through EAATs and reconverted into glutamate.
Which type of neurotransmitter receptor is gated by transmitter, has some ion selectivity, inactivates after use, and can have its conductance modified by phosphorylation?
Ionotropic
True or False?:
Spiny neurons receive EPSPs on their spines while non-spiny neurons simply receive EPSPs on their shafts.
True
Where are excitatory synapses typically found? Where are inhibitory synapses typically found?
Excitatory synapses are typically found on spines. Inhibitory synapses are typically found on the soma or dendritic shaft.
True or False?:
Most excitatory ionotropic receptors are chloride channels. Inhibitory ionotropic receptors are non-selective cation channels. A few are also permeable to calcium.
False
Most excitatory ionotropic receptors are non-selective cation channels. A few are also permeable to calcium. Inhibitory ionotropic receptors are chloride channels.
True or False?:
Cholinergic receptors are non-specific cation channels because they allow any ions with a +1 charge to go through.
True
How is it known that cholinergic channels are permeable to both potassium and sodium and impermeable to chloride and calcium?
If you lower the external sodium concentration, the cholinergic reversal potential becomes more negative. If you increase the external potassium concentration (decrease the potassium gradient across the membrane), the cholinergic reversal potential becomes more positive. If you change the external chloride or calcium concentration, nothing happens to the cholinergic reversal potential.
What are the two classes of neurotransmitter receptors?
Ionotropic (Ligand-Gated Ion Channels) and Metabotropic (G-Protein-Coupled Receptors)
How do the vesicle and synapse shapes differ between excitatory and inhibitory synapses?
Excitatory synapses have round vesicles and an asymetrical post-synaptic density. Inhibitory synapses have flat vesicles and a symmetrical post-synaptic density.
What is happening in each stage of the attached diagram displaying EPCs and EPPs of cholinergic receptors?
A - At the reversal potential of potassium, only sodium ions will flow. They will flow into the cell (creating an inward end-plate current) and result in a depolarizing end-plate potential.
B - When the membrane potential is higher than the reversal potential of potassium, both ions will flow, though in opposite directions. The EPC and EPP will be in the same directions, but have slightly smaller magnitudes due to the potassium opposition.
C - At 0 mV, both ions pass through the channel in equilibrium resulting in no EPC or EPP. This is the reversal potential for the whole channel.
D - At the reversal potential of sodium, only potassium ions will flow. They will flow out of the cell (creating an outward EPC) and result in a hyperpolarizing EPP.
