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Title: Physiology Lesson 4 Synapses
Description: University Major Level Physiology Notes , Describes synapses
Description: University Major Level Physiology Notes , Describes synapses
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Lecture 4: Synapses
No t e b o o k:
C re at e d :
Physiology
8/16/2012 9:46 AM
U p d at e d :
8/16/2012 10:26 AM
Synapses: are junctions between excitable cells
...
Permits impulses (APs) to be conducted directly from
one cell to another
...
Will be
covered ahead
...
but it could really be any combination of excitable pre-synaptic
and post-synaptic cells)
Pre-Synaptic Cell: In the neuromuscular junction the AP travels from the nerve to
the muscle, NOT the reverse (so Nerve is Pre-synaptic cell in this case)
Transfers information to the post-synaptic cell
has lots of mitochondria (an indication of alot of "stuff" going on)
Also has 2 membrane bound vesicles types that aid in Synaptic Transmission
Releasable Vesicle: can be released into the space between the preand post-synaptic cell (the synaptic cleft)
They are fused to the membrane of the pre-synaptic cell near
the cleft, by special proteins (SNARE COMPLEX) and are READY
TO BE RELEASED
The hold neurotransmitters and are not released into the
cleft until stimulated
Reserve (Storage) Vesicles: hold neurotransmitters and are held
away from the releasable area, awaiting the chance to become
releasable (When an AP releases the releasable vesicles a reserve one
takes its place)
They are attached to actin fibers (don't just float in cytoplasm)
Connected by molecules of Synapsin which is found in the
vesicle membrane
Post-Synaptic Cell
Receives signal from pre-synaptic and performs function
Mechanism of Synaptic Release
Action potential arrives at Pre-synaptic terminal
Causes Depolarization and opening of Voltage gated Ca(2+) Channels as well as
Voltage Gated Na+ Channels
Ca(2+) ions diffuse into the cell
causes exocytosis of SNARE vesicles, causes Releasable Vesicles to diffuse
and release Neurotransmitter into the cleft
Ca(2+) also binds with calmodulin, to form Calcium Calmodulum which
activate Protein Kinases (add a Phosphate Group to a molecule, usually
"activating" said molecule)
Protein Kinases phosphorylate synapsins turning Reserve Vesicles into
Releasable Vesicles
Neurotransmitter (ligand, in this example it is 2 Acetylcholine molecules, also called
Ach) opens a ligand-gated channel in the post-synaptic membrane, by chemically
binding to the receptor site on it
This allows for Na+ to be pushed in and K+ out, creating change in membrane
potential of the Post-synaptic cell
After Binding to the post-synaptic cell and causing an AP in it (in most cases), Ach is
broken down by Acetylcholine Esterases (Achesterases) to acetate, which
diffuses out and choline, which stays in the cleft
FEATURED TOXIN: Botulism Toxin
functions as a protease that digests specific components of fusion complex
Destroys SNARE complex needed for exocytosis of Ach and causes flaccid paralysis
Title: Physiology Lesson 4 Synapses
Description: University Major Level Physiology Notes , Describes synapses
Description: University Major Level Physiology Notes , Describes synapses