Unit 4 Flashcards
Where do synapses form? (CNS and muscle)
CNS: excitatory glutamatergic synapses form on the dendritic spines; inhibitory GABAnergic synapses form on the cell soma
Muscle: they form in the middle of the myofibers
The constituents that make up a synapse are already ____.
are already present in cell waiting to coalesce in the right location.
What does dying the neurotransmitters in a growth cone reveal? And how was this done?
The dye reveals that neurotransmitters are released from the growth cone upon contact with receptor neurons.»_space; Vesicular release must occur before synapse formation.
The neuron was depolarized to generate vesicles which took up dye from the environment during polarization. When the neuron was repolarized by signal transmission, the dye release would be observable.
What does the myoball assay show?
That contact strength increases over time between a neuron and its target cell.
What are “puncta adherentia”?
adhesion junctions; the zone of adhesion between the pre- and postsynaptic cell
Cell adhesion is dependent upon which molecules? ___ and ___.
cadherins and nectins; together, they allow for tight binding at the adhesion junctions.
What does the experiment involving synaptophysin and PSD95 show? (And what are PSD95 and synaptophysin?)
PSD95: a marker for the postsynaptic density
synaptophysin: a marker for presynaptic transport packets
The experiment showed that presynaptic transport packets are recruited to the synapse due to communication between pre and postsynaptic signals. The synapse is stabilized due to the interactions between the postsynaptic density and the presynaptic proteins.
What are neurexin and neuroligin? and what does their interaction lead to?
Neurexin is a presynaptic receptor and neuroligin is a postsynaptic receptor.
Binding of NRXN to NLGN induces presynaptic differentiation.
What does clustering before innervation reveal about postsynaptic differentiation in the muscle? How was this shown?
Acetylcholine receptors (AchR) are present in the post-synaptic cell. Bungarotoxin is used to block these receptors so they cannot communicate. However, PSD clustering still occurs because communication with presynaptic cells isn’t necessary for clustering to occur in the postsynaptic region.
Cell-to-cell contact is important for organizing the synapse, NOT ligand-receptor interactions.
What is bungarotoxin?
Bungarotoxin is a molecule that binds to AchRs and blocks their activation.
Explain the mechanism of postsynaptic AchR clustering determined using Xenopus muscle.
Normally, motor neurons are connected through the basal lamina to target muscle cells with AchRs. If the nerves are cut, the AchRs still cluster to the same location in the basal lamina.
This indicates that there is some extracellular matrix component responsible for clustering near the postsynaptic receptors.
What is the basal lamina?
the protein-rich region in the ECM between neurons and their target cells
What is the component that encourages AchR clustering in the basal lamina?
Agrin
How does Agrin work?
Agrin is a ligand found in the ECM. It binds a co-receptor Lrp4 to MuSK, a receptor in the membrane of the postsynaptic target cell. MuSK provides the downstream scaffold for AchR clustering.
Ach ___ the formation of its receptor when agrin isn’t present.
inhibits
aggregation of AchRs only occurs where agrin is present. this prevents the acetylcholine signal from spreading too far.
___ play a role in CNS receptor clustering
Ephrins
Glutamate receptor clustering depends upon
Ephrin-Eph signaling
Four things that occur after synaptogenesis starts:
Recruitment of receptors to synapse increase
Transcription of new receptors
Recycling time of receptors decreases
Translation of receptors in the dendrites increases
