Structure of a chemical synapse in the brain: pre and post synaptic mechanisms (Dr. Edwards) Flashcards
Do dendrites always project on one side of the axon ?
Not at all. There can be basal dendrites as well.
How many axons leave the soma ?
ONE, and only ONE.
What are two types of cells that illustrate the dendritic heterogeneity in neurons ?
Parking cells of the cerebellar cortex are very arborated on one side of the soma and on the other side a single axon carries the info to the presynaptic terminal.
Pyramidal neurons in the neocortex generally have less branched dendrites, which are both apical and basal.
How bing is the axon compared to the dendrites ?
The axon is usually longer (but very variable, 10μs-meters) and thinner than dendrites (again, thickness varies depending on myelination) whilst dendrites tend to be shorter (10-100μms) and tapering.
How is communication w/in and between 2 or more neurons different ?
Communication w/in one given neuron travels as an “all or none” AP.
Communication from one neuron to another occurs in the form of a graded potential, a PSP (Post Synaptic Potential).
How wide is the synapse ?
How long is the synaptic divide ?
About 1 μm, can be smaller.
Between 15-40nm.
What are the main types of receptors on a postsynaptic neuron ?
AMPA (α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors/channels, NMDA (N-methyl-D-aspartate) receptors/channels, kainate receptors, metabotrobic receptors, but also AMPA quantal clusters (ask Dr. Edwards).
On which side of the synapse are there more mitochondria ?
Why ?
The presynaptic side.
Mitochondria are important for clearing calcium from the synaptic terminal.
What is the active zone ?
Site of neurotransmitter release.
What is the PSD (Post Synaptic Density) ?
The PSD is a protein dense specialization attached to the postsynaptic membrane. PSDs were originally identified by electron microscopy as an electron-dense region at the membrane of a postsynaptic neuron.
What are the main proteins involved in neurotransmitter release ?
The SNARE proteins: v-SNAREs and t-SNAREs, synaptotagmins, and synapsins.
What are the different kinds of SNARE proteins ?
v-SNARE is associated w/ the vesicle (synaptobrevin is part of this sub-family)
t-SNARE is associated w/ the membrane
SNAP-25/synapsin complex = t-SNARE complex
Where is synaptotagmin and what does it do ?
It is a vesicle associated protein that binds calcium to trigger neurotransmitter release.
What are synapsins and what do they do ?
Synapsins are a family of proteins that bind synaptic vesicles to components of the cytoskeleton which prevents them from migrating to the presynaptic membrane and releasing neurotransmitter.
Upon phosphorylation, synapsins release the vesicles.
Describe one theory explaining the mechanism of neurotransmitter release ?
Once calcium ions bind to synaptotagmin, the t-SNAREs and v-SNAREs bind and “zip” together about halfway through. This forms the 7S complex.
Synaptotagmin then binds this structure w/ SNAP and NSF (N-ethylmaleimide Sensitive Fusion) protein to form the 20S complex. Upon hydrolysis of ATP to ADP, the SNAREs completely “zip together” so that the vesicle fuses totally w/ the membrane and its neurotransmitter is released into the cleft.
