Synapses & Signal Integration

Question 1

What are boutons?

Answer 1

Specialized sites where neurons communicate by release of neurotransmitters

Question 2

Small molecules that transmit impulses at chemical synapses

Answer 2

Neurotransmitters

Question 3

Main excitatory neurotransmitter

Answer 3

Glutamate

Question 4

Main inhibitor neurotransmitter

Answer 4

GABA

Question 5

What are the three criteria for a neurotransmitter?

Answer 5

• Present in the nervous system in pre-synaptic terminals
• Released in response to pre-synaptic depolarization in a Ca2+ dependent manner
• Specific receptors exist for the transmitter on post-synaptic cells that generate a signal in the post-synaptic cell

Question 6

What are the steps in synaptic transmission?

Answer 6

1. Action potential in nerve terminal opens Ca2+ channels
2. Ca2+ entry causes vesicle fusion and transmitter release
3. Receptor-channels open, Na+ enters post-synaptic cell and vesicles recycle

Question 7

T or F. Under most conditions, membrane potential changes occur only with significant change in ion concentration.

Answer 7

FALSE - membrane potential changes occur with LITTLE change in ion concentration under most conditions

EXCEPTION: when Ca2+ channels are active, significant concentration changes do occur for intracellular Ca2+

Question 8

Electrical signaling often results in a ____ influx to transduce the electrical signal into other biochemical signals.

Answer 8

Ca2+

Question 9

Where are Ca2+ channels position in the pre-synaptic bouton?

Answer 9

Directly below the active zone

Question 10

What machinery in the synapses is a target of bacterial toxins?

Answer 10

Fusion machinery

Question 11

T or F. Vesicles are destroyed after releasing neurotransmitter.

Answer 11

FALSE - they are recycled and reused

Question 12

What is channel gating?

Answer 12

Conformational changes that affect channel open probability

Question 13

What are 4 common gating mechanisms?

Answer 13

1. Voltage-gated
2. Ligand-gated (extracellular molecule)
3. Signal-gated (intracellular molecule)

Question 14

What are the main receptors found at excitatory synapses? What type of ion do they allow to pass through the channel?

Answer 14

Ionotrophic glutamate receptors

Cations

Question 15

Opening of the glutamate receptor channel is near 0 mV so opening it drives membrane potential to _____ (depolarize/hyperpolarize)

Answer 15

Depolarize

Question 16

_____ ensures that ionic currents will go to 0 if conductance is kept constant.

Answer 16

System attractor point

Question 17

____ shift system attractor point toward channel’s 0 current potential if conductance is _____ or away if conductance is _____

Answer 17

Channel conductance changes

Increasing

Decreasing

Question 18

Are glutamate receptors open or closed at rest? Why?

Answer 18

Closed - because opening it requires a torqued conformation which is not energetically favorable

Question 19

Ligand binding to glutamate receptors only stabilizes the _____ state (activated or closed)

Answer 19

Activated

Question 20

Where is glycine primarily used as a neurotransmitter? Is it excitatory or inhibitory

Answer 20

Spinal cord - inhibitory

Question 21

Excitatory sites primarily use ____ channels, while inhibitory sites primarily use ____ channels

Answer 21

Cation

Cl-

Question 22

Where in the neuron are synaptic responses generated? Where are action potentials produced?

Answer 22

Dendrites

Soma and hillock

Question 23

For sustained current injections, the signals decay exponentially with distance with a characteristic _______

Answer 23

Space Constant

Question 24

For passive spread of signals in neurons, _____ membrane resistance and _____ axial resistance increase the space constant

Answer 24

Higher

Lower

Question 25

For transient current injections, the signals decay even faster with distance due to _____

Answer 25

charging of the membrane capacitance

Question 26

What are complicating factors for signal propagatino?

Answer 26

• Varying dendritic branch diameters
• Varying distance of inputs from the soma
• Voltage-gated channels that reshape basic synaptic responses

Question 27

T or F. An action potential can be generated with a single synaptic event.

Answer 27

FALSE - many small synaptic events must sum together to reach threshold

Question 28

Simultaneous stimulation of two connections

Answer 28

Spatial summation

Question 29

Sub-linear summation

Answer 29

If two EPSP synaptic events occur together within an electrically overlapping compartment, then they will affect the currents being generated and summate in a sub-linear fashion

Question 30

Linear summation

Answer 30

If EPSPs are generated in electrically distant compartments, then they will sum almost linearly since each generates independent currents that will reach the soma and work together to drive membrane depolarization

Question 31

Repetitive stimulation of same connection

Answer 31

Temporal summation

Question 32

What is rate limiting step for response termination?

Answer 32

Elimination of transmitters within synaptic cleft or for higher affinity receptors, neurotransmitter unbinding from receptor

Question 33

Temporal summation is ____ (linear/sub-linear)

Answer 33

Sub-linear

Question 34

If receptor population is overlapping, there will be competition between transmitters for the same receptors, producing ____(linear or sub-linear) summation.

Answer 34

Sub-linear

Question 35

What are the three types of coordinated activity of excitatory and inhibitory synapses?

Answer 35

1. Feedback
2. Feed-forward
3. Lateral inhibition - winner take all