Presynaptic mechanisms Dr. Chirwa Flashcards
What is the major form of communication within the nervous system?
Communication is done via SYNAPSES
How does a synapses work?
Communication signals are transmitted from the upstream neuron (presynaptic) to the downstream (postsynaptic) neuron
What is the functional contact between neurons?
Synapses
What are the two types of neurons?
Electrical and chemical
How does an electrical synapses work?
Current will flow through gap junctions (membrane channels that connect two cells together)
How does a chemical synapses work?
Neurotransmitters (chemical) are released to enable cell-to-cell communication.
What do gap junctions contain?
-Hexameric complexes formed by subunits (connexons channels)
-Connexons contain the integral protein connexin
- Connexons will provide the path pr “channel” to allow current to flow through
How does the postsynaptic neuron become depolarized?
From action potential in presynaptic neurons
Is there direct or indirect current flow for chemical synapses?
Indirect flow. There will be no direct flow for chemical synapses due to there being no intercellular continuity
What is the purpose of synapsin?
Synapsin will keep the vesicles (neurotransmitters) held together until a single vesicles is ready for the docking process
What is the docking process of a vesicle?
Docking process: The synapsin that’s holding the vesicle’s together will release 1 vesicle at a time. Once the vesicle is free, it will dock closer to the plasma lamina to get ready to be released
What happens after the vesicle has docked?
Ca2+ will enter the cell and signal for the vesicle to be released from the docking stage. The vesicle will then travel to the postsynaptic neuron to release the intended neurotransmitter.
What is the purpose of Clathrin?
Clathrin will help close the entry/exit point from where the Ca2+ and vesicle entered/exit by ENDOCYTOSIS
Purpose of Synaptobrevin?
To hold and bring the vesicle closer to the plasma lamina membrane.
Purpose of SNAP-25?
To hold Synaptobrevin and Syntaxin together while they work together to bring the vesicle closer to the membrane
Purpose of Syntaxin?
To attach to the plasma membrane lamina while holding onto Synaptobrevin
Purpose of Synaptotagmin?
Synaptotagmin is a signal for Ca2+ to be released into the membrane. Ca2+ will bind to synaptotagmin . The vesicle will be released after this last signal (neurotransmitter will be released to the postsynaptic)
SNARE proteins:
Syntaxin
Synaptobrevin
SNAP-25
Synaptotagmin
What will toxins from Clostridial toxins do?
Toxins will cleave SNARE proteins resulting leading to inhibiting transmitters
What will BOTULINUM toxin block?
the release of excitatory Acetylcholine at the NMJ
What does TETANUS toxin block?
the release of inhibitory transmitters Glycine and GABA
What causes paralysis of neuromuscular synapses and skeletal muscle weakness?
Botulinum toxin blocking the release of ACH
How long does it take for a vesicle to be recycled to be reused?
1min
Lambert-Eaton Myasthenic syndrome:
antibodies will bind to Ca2+ channels and disrupt neuromuscular transmission
What is the criteria for identifying as a neurotransmitter?
Must include:
Synthesis
Storage
Release
Mimicry
Inactivation
What are the two types of neurotransmitters?
Small molecule transmitters
Peptide transmitters
Where are small molecule transmitters made?
At the terminal region of the axon
Where are the enzymes made for small molecule transmitters?
Inside of the SOMA (cell body).
How are the small molecule transmitter enzymes made?
From slow anterograde transport (0.5-5mm/day). Not dependent on microtubules or ATPase motor molecules
Where are the peptide transmitters and enzymes synthesis at?
SOMA (cell body)
What are the peptide transmitters transported by ?
Fast anterograde transport (100-400 mm/day). Dependent on Kinesin (ATPase). Will be stored at the synaptic region until ready for transport
T/F: Vesicle can contain more than 1 type of transmitter?
True
How is Glutamate terminated?
By the uptake of glial cells via transporters. Glutamate will then be converted into glutamine. Glutamine is then taken up nerve terminals and converted back into glutamate
What is the predominant precursor for GABA?
Glucose. Pyruvate and glutamine can also act as GABA precursors
What does Acetylcholine serve as?
The neurotransmitter at the neuromuscular junction
