lecture 11 inhibition and integration Flashcards
excitatory synapses
increasing the likelihood that the neuron fires an action potential
inhibitory synapse
where the release of neurotransmitter decreases the likelihood that the postsynaptic neuron
fires an action potential
Axodendritic synapse
a presynaptic axon that establishes a synapses onto a
dendrite or spine of the postsynaptic cell. Synapses onto spines and distal axodendritic
synapses are typically excitatory
Axosomatic synapse
a presynaptic axon that establishes a synapses onto the soma
(cell body) of the postsynaptic cell. Axosomatic synapses are often inhibitory
Axoaxonic synapse
a presynaptic axon that establishes a synapses onto the axon or
an axon terminal of another cell. These synapses are often inhibitory and can prevent
the other presynaptic neuron from releasing vesicles
GABA
found at brain/central nervous system inhibitory synapses
Glycine
found in spinal cord inhibitory synapses
receptors for cns inhibitory synapse neurotransmitters
GABA “A” receptor and GlycineR
how are achr and gaba/glycine receptors different
They are similar in structure to the acetylcholine receptor
(nAChR) except: 1. An affinity for different neurotransmitters (GABA or Glycine as opposed to
ACh) and 2. The channel pore (the M2 membrane spanning domains) is lined by positively
charged amino acids, as opposed to negative charges in the AChR. This means the channels
are selective for anions, specifiacally Cl-
Shunting inhibition
even though the reversal potential (ECl) for inhibitory synapses is
approximately the resting membrane potential, the opening of GABA channels is very
effective in preventing the postsynaptic neuron from reaching threshold. This inhibition
essentially allows Cl- entry anytime the membrane potential is depolarized. This shunts
the excitatory synaptic current
Presynaptic inhibition
when an inhibitory neuron makes a synapse on the
presynaptic terminal of another neuron. The inhibitory synapse causes a reduction in
the conductance of voltage-gated Ca++ channels, and a decrease in synaptic release
Synaptic integration
the manner in which multiple spatially or temporally distributed
synaptic potentials sum
axon initial segment
also known as the “trigger zone” determines if a neuron fires an action potential or not
The axon initial segment has the highest
density of voltage-gated Na+ channels and therefore the lowest threshold value. Typical
membrane potentials for threshold (Vthresh) are between -30 - -45 mV depending on channel
density, cell morphology, and which subtypes of voltage-gated channels are expressed
a synaptic potential (or summation of potentials) that does
not cause depolarization above threshold above action potential potential
Subthreshold potential
a synaptic potential (or summation of potentials) that does
elicit an action potential
Suprathreshold potential
Synaptic Attenuation
EPSPs in dendrites obey cable properties and their amplitudes
will decrease along the length of the dendrite. (See lecture 6 for cable properties.) Thus
a synapse on a distal branch will cause a smaller depolarization at the soma or initial
segment than a similar size synapse on a proximal dendrite (close to the soma)
Non-linear synaptic summation
multiple EPSPs will not linearly summate (i.e. the
final amplitude is less than the sum of individual amplitudes) because the synaptic
potential cannot exceed the reversal potential and gets progressively smaller the closer
the membrane potential gets to the reversal potential
Concurrent Inhibition during temporal summation
inhibition occurring at the same
time activation of excitatory synapses can prevent temporal summation as inhibition not
only the decreases EPSP amplitude, but also reduces membrane resistance (opens
additional channels which ions can flow through) which shortens the decay time course
of the EPSP.
- Explain what makes a synapse inhibitory and the ionic basis of inhibition.
- List the most common inhibitory neurotransmitters in the CNS and PNS.
Know where inhibitory synapses are located on the neuron and how their location and
receptor properties (including ECl) relate to the IPSP shape
Be able to describe and apply the following factors that regulate the effectiveness of
synapses:
* distance from initial segment of an axon
* non-linear summation
* shunting IPSPs
* temporal summation
* temporal summation with concurrent inhibition
strychnine
decreases glycine’s ability to conduct chlorine, blocks inhibition so too much excitation and overactive muscles cause convulsions while wide awake, body rigor
Picrotoxin
inhibits gaba a receptor and causes rigidity, convulsions, seizures
what do agonists do
enhance chloride conductance
examples of agonists
barbiturates (truth serum, capital punishment), benzodiazepines (anti anxiety, sleep, muscle relaxer)
alcohol, neurosteroids, general anesthetics
example of psychiatric illness and disorders related to inhibitory transmission
startle diseases, fainting goat
the farther way from the trigger zone a synapse is
the less powerful it is
dendrites allow addition of the excitatory synaptic contributions of many inputs to sum at the
soma
is summation voltage linear or non linear
non linear- not the arithmetic sum of each of he synaptic potential amplitudes, because the closer the membrane potential gets to reversal potential (10 in excitatory synapses) the lower the net driving force
a synapse cant depolarize the membrane beyond its reversal potential so adding many synapses together can only approach 10, and each additional input has less effect
ipsps interposed between an epsp and the initial segment…
block the epsp from reaching threshold
