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the connexon of one membrane is precisely align to the connexon of the next membrane, so
that the water-filled pore (channel) directly perforate both membrane directly, going from
intracellular fluid of one cell to another.
these gap junctions channels are bi-directional. they readily pass current and small organic
molecules in both direction. Again, commonly found in cells whose electrical or metabolic
activity need to be coordinated. this happen a lot during in embryonic development where lots of
adjacent cells are connected via gap junctions. this is important in passage of secondary
messenger or multiple genetic signal from cell to cell. At some point in development, gap
junction cease to be express, they are remove from membrane and cell within tissue become
metabolically isolated from one another.
there are some regulations of the permeability or conductance of gap junction channels. gap
junction channels are subject to negative regulation by calcium ion or hydrogen ion (proton),
either in increase in intracellular calcium ion or intracellular proton (drop in pH) will close the gap
2. chemical Post- Channels may close
in response to:
Connexin Connexon Negative stain EM
of gap junction Presynaptic membrane 3 nm Postsynaptic membrane Gap junctions
cardiac cells Current exiting
connexon channel Steps in Chemical Synaptic Transmission
the next is chemical synaptic transmission. chemical is more ubiquitous in vertebrae nervous
-information is going left to right.
1. the first step is synthesis of transmitter. the neural transmitter, T, is enzymatically synthesized
from a precursor molecule P within pre-synaptic terminal. this apply to all neural transmitter
except peptide neurotransmitter. this means that all neurotransmitter are synthesized locally
within presynaptic terminal. everything involve in synthesis is contain within the terminal. for
peptide it's different because only in soma of neuron locate the machinery of ribosome, golgi
necessary for synthesis and modification of peptide and proteins. in th...
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This document was uploaded on 03/09/2014 for the course EXSC 301 at USC.
- Spring '09