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Lecture 9

Lecture 9 - Communication Between Neurons

8 Pages
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Department
Biological Sciences
Course Code
BIOC32H3
Professor
Kenneth Welch

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Lecture 9 Communication between neurons
Electrical synapse function
Figure we can inject a stimulus current into the presynaptic terminal and injecting
supra-concentration (?) sub-threshold so that delpol occurs
Reduce resistance by increasing # of gap junctions?
(Diagram c)
Rectifying electrical synapse
Gap junctions can be directional depending on which cell depolarizes first
Rectifying = one way only
Fast chemical synapse
In a fast chemical synapse, area is very small
Ca+ influx triggers exocytosis of vesicles into the synaptic cleft
Neurotransmitters bind to post-synaptic membrane receptors
oIn the case of an excitatory synapse, influx into the post-synaptic membrane
Transmitter is removed/degraded in cleft
Less and less ligand binding where there is a fast chemical synapse
If the post synaptic membrane is only permeable to K+ then it is an inhibitory
synapse influc oc K+ causes hyperpolarization
Neurotransmitters and fast chemical synapses
Ach: common
Doesnt depend on the neurotransmitter but the receptors involved
www.notesolution.com
Nicotinic
An agonist, mimicking effects of Ach
Ligand in this case is Ach
If in patch-clamp, we hold the membrane much more negative than normal and then
we have a solution in our path-clamp that has agonist (nicotine), that _______...
Stages:
oDesensitized: wont be able to reopen until ach unbinds and returns to resting
state
Ach is essentially equally permeable to Na+ and K+ - but why is it the case that it is
an excitatory receptor??
EMF:
EMF for NA = -110 mV
oIs a very negative, strong gradient which allows positive influx of current
into the cell
Ionic Conductance
Permeability is inversely related to resistance
If conductance is low, current is low (g=conductance)
Reversal Potential
When the current from one ion is equal and opposite to another
If the relative permeabilities are equal (therefore it is ratio of 1) then both is ½ of
that
GABA:
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Cl- is going to move toward its equilibrium potential which is net Cl- entry into cell
Driving membrane potential to its equilibrium potential
Slow chemical synapse
Larger molecules (but not always true ACH works as a slow too)
Not specifically released at active site
Other, indirect, route to get to post-synaptic membrane
Mechanism:
oActs by way of second-messenger systems indirect change in conductance of
a nearby channel when neurotransmitter binds to a receptor
oSynaptic activity can be SUPERIMPOSED on a fast chemical synapse and
modify its activity
oLonger term changes modifying expression of genes/proteins and changing
metabolism
EPSPs and IPSPs
Readings:
Chapter 6 Communication Along and Between Neurons Section Transmission of
Information Between Neurons through Integration at Synapses P. 166 –202.
Transmission of Information Between Neurons
Electrical synapses: the presynaptic neuron is electrically connected to the
postsynaptic neuron by proteins within the membranes; relatively rare
Chemical synapses: APs in the presynaptic neuron case the release of
neurotransmitters that diffuse across a narrow space called the synaptic cleft that
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Description
Lecture 9 Communication between neurons Electrical synapse function Figure we can inject a stimulus current into the presynaptic terminal and injecting supra-concentration (?) sub-threshold so that delpol occurs Reduce resistance by increasing # of gap junctions? (Diagram c) Rectifying electrical synapse Gap junctions can be directional depending on which cell depolarizes first Rectifying = one way only Fast chemical synapse In a fast chemical synapse, area is very small Ca+ influx triggers exocytosis of vesicles into the synaptic cleft Neurotransmitters bind to post-synaptic membrane receptors o In the case of an excitatory synapse, influx into the post-synaptic membrane Transmitter is removeddegraded in cleft Less and less ligand binding where there is a fast chemical synapse If the post synaptic membrane is only permeable to K+ then it is an inhibitory synapse influc oc K+ causes hyperpolarization Neurotransmitters and fast chemical synapses Ach: common Doesnt depend on the neurotransmitter but the receptors involved www.notesolution.com
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