Neuro Lecture B4 Flashcards
Ionotropic Receptor
receptor, that when activated by an appropriate agonist, functions as an ion channel when appropriately stimulated
Metabotropic Receptor
Receptor that when activated by an appropriate agonist, interacts with a G protein to produce a change of enzyme activity within the postsynaptic cell
what are the two basic types of synapses?
Electrical and Chemical
Electrical Synapses synchronize which cells in the CNS?
Hormone-secreting cells of the hypothalamus-pituitary axis, some spinal motor neurons, hippocampal pyramid cells, mesencephalic nuclear cells and retinal cells
In electrical synapses what allows ions to move from one cell to the next?
Gap Junctions (astrocytes) also communicate this way as well
electrical transmission through gap junctions is very fast or very slow?
Very fast (under 0.1ms) and can be either unidirectional or bidirectional
Are most vertebrate synapses chemical or electrical?
chemical, with neurotransmitters being released by presynaptic cells and binding to the post synaptic receptors
The presynaptic membranes have special ??? where exocytosis occurs
Active Zones
Neuronal Chemical Synapses are located ?
on dendrites, cell bodies, axon hillocks, and close to synaptic boutons at the axon terminals
Do most axodendritic synapses excite or inhibit the postsynaptic neuron?
Excite (therefore increasing the likelihood of action potentials)
Do most axosomatic synapses inhibit or excite the postsynaptic neuron?
Inhibit (decreasing the probability of action potentials)
Do most axoaxonic synapses excite or inhibit the ability of action potentials to provoke release of the transmitter?
Inhibit
Explain the main points of Tripartite Synapses
- Exists among presynaptic and postsynaptic neurons and astrocytic endfeet
- Astrocytes take in glutamate (released by neurons)
- And release glutamine for absorption by neurons
So this is really an exchange of glutamate for glutamine
what is the criteria to be considered a neurotransmitter?
- Synthesis is presynaptic neurons
- storage in preparation for release
- release by presynaptic neurons, typically in a calcium dependent fashion
- Binding to specific postsynaptic receptors, thereby exerting stereotyped cellular effects
- Removal from synapses by specific mechanisms
Small molecule (low molecular weight) transmitters under what kind of synthesis
Cytosolic and loaded into clear vesicles for tethering to the cytoskeleton near the active zones in preparation for release
Neuropeptide (High molecular weight) transmitters arise from where?
Propeptides, which are synthesized in the soma and travel to the nerve ending by anterograde axonal transport.
Storage compartments for what neurotransmitter does not exist?
Storage compartments for NO do not exist.
How does Nitric Oxide (NO) transmitter arise?
from the interaction of nitric oxide synthase (NOS) and I-arginine
what activates the Nitric Oxide Synthase
Calcium-Calmodulin complex
Sometimes the process for filling synaptic vesicles involves the movement of H ions. Give an example of this?
Vesicular membranes may express antiports that exchange dopamine (DA) for H (so basically the antiport substitutes the transmitter (DA) for hydrogen), this is done due to the H+ ATPase
First step in exocytosis
- Synapsin tethers vesicles to the cytoskeleton
Second step in exocytosis
Phosphorylation of synapses by calcium calmodulin dependent protein kinase liberates vesicles from the cytoskeleton
Third step in exocytosis
- Rab Proteins facilitate movement of vesicles towards the active zones for exocytosis
Fourth step in exocytosis
- Docking of the vesicles with nerve terminal membrane depends upon binding of SNARE membrane proteins
which membrane has v-SNARE proteins and which has t-SNARE proteins?
vesicular membranes have v and nerve membrane has t
describe the binding of the different SNARE proteins
v-SNARE protein synaptobrevin binds to t-SNARE protein syntaxin
v-SNARE protein synaptotagmin binds to t-SNARE protein neurexin
5th step in exocytosis
After docking, the vesicular membrane protein synaptophysin probably forms the fusion pore in the nerve terminal membrane, allowing release of transmitter.
Voltage gated calcium channels open in reaction to an action potential. The action potential-dependent influx of calcium is necessary for what process?
exocytosis
The quick rise in Ca in the active zone facilitates the opening of the inserted fusion protein allowing what to happen?
allowing transmitters to leave the vesicle and enter the synaptic cleft
At low stimulation rates the rise in Ca2+ occurs nears the active site, permitting exocytosis of what specifically?
small clear vesicles containing small molecule transmitter
At high stimulation rates the rise in Ca2+ spreads further and thereby promoting exocytosis of what specifically?
promoting exocytosis of large dense core vesicles containing peptides.
What happens to the membranes of small clear vesicles after exocytosis?
recycled locally in the nerve terminals. this is mediated by the protein Clathrin, which coats the vesicle.
what happens to the membranes of dense core vesicles?
empty vesicles are transported retrogradely to the soma for refilling. (rate of retrieval is slow which is in contrast with the rapid rate of uptake)
explain what an ionotropic receptor does
transmitters diffuse across the synaptic cleft and bind to receptors. Some receptors (ionotropic) change confirmation when binding an agonist, either opening or closing a central ion passing pore. this will shift the membrane potential
give some examples of ionotropic receptors
Nicotinic AChR; GABA receptor; and NMDA receptor for glutamate.
explain metabotropic receptors
act via G proteins, which influences enzymes and therefore second messengers. these second messengers activate cascades of intracellular signaling
examples of metabotropic receptors??
muscarinic AChR and norepineprine receptors
the signaling cascades in metabotropic receptors active what?
kinases, liberate calcium and promote phosphorylation of channels for K, Ca, and Cl
