lecture 11 inhibition and integration

Question 1

excitatory synapses

Answer 1

increasing the likelihood that the neuron fires an action potential

Question 2

inhibitory synapse

Answer 2

where the release of neurotransmitter decreases the likelihood that the postsynaptic neuron
fires an action potential

Question 3

Axodendritic synapse

Answer 3

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

Question 4

Axosomatic synapse

Answer 4

a presynaptic axon that establishes a synapses onto the soma
(cell body) of the postsynaptic cell. Axosomatic synapses are often inhibitory

Question 5

Axoaxonic synapse

Answer 5

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

Question 6

GABA

Answer 6

found at brain/central nervous system inhibitory synapses

Question 7

Glycine

Answer 7

found in spinal cord inhibitory synapses

Question 8

receptors for cns inhibitory synapse neurotransmitters

Answer 8

GABA “A” receptor and GlycineR

Question 9

how are achr and gaba/glycine receptors different

Answer 9

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-

Question 10

Shunting inhibition

Answer 10

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

Question 11

Presynaptic inhibition

Answer 11

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

Question 12

Synaptic integration

Answer 12

the manner in which multiple spatially or temporally distributed
synaptic potentials sum

Question 13

axon initial segment

Answer 13

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

Question 14

a synaptic potential (or summation of potentials) that does
not cause depolarization above threshold above action potential potential

Answer 14

Subthreshold potential

Question 15

a synaptic potential (or summation of potentials) that does
elicit an action potential

Answer 15

Suprathreshold potential

Question 16

Synaptic Attenuation

Answer 16

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)

Question 17

Non-linear synaptic summation

Answer 17

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

Question 18

Concurrent Inhibition during temporal summation

Answer 18

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.

Question 19

1. Explain what makes a synapse inhibitory and the ionic basis of inhibition.

Question 20

2. List the most common inhibitory neurotransmitters in the CNS and PNS.

Question 21

Know where inhibitory synapses are located on the neuron and how their location and
receptor properties (including ECl) relate to the IPSP shape

Question 22

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

Question 23

strychnine

Answer 23

decreases glycine’s ability to conduct chlorine, blocks inhibition so too much excitation and overactive muscles cause convulsions while wide awake, body rigor

Question 24

Picrotoxin

Answer 24

inhibits gaba a receptor and causes rigidity, convulsions, seizures

Question 25

what do agonists do

Answer 25

enhance chloride conductance

Question 26

examples of agonists

Answer 26

barbiturates (truth serum, capital punishment), benzodiazepines (anti anxiety, sleep, muscle relaxer)
alcohol, neurosteroids, general anesthetics

Question 27

example of psychiatric illness and disorders related to inhibitory transmission

Answer 27

startle diseases, fainting goat

Question 28

the farther way from the trigger zone a synapse is

Answer 28

the less powerful it is

Question 29

dendrites allow addition of the excitatory synaptic contributions of many inputs to sum at the

Answer 29

soma

Question 30

is summation voltage linear or non linear

Answer 30

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

Question 31

ipsps interposed between an epsp and the initial segment…

Answer 31

block the epsp from reaching threshold