Flashcards in Synapses & Signal Integration Deck (35):
What are boutons?
Specialized sites where neurons communicate by release of neurotransmitters
Small molecules that transmit impulses at chemical synapses
Main excitatory neurotransmitter
Main inhibitor neurotransmitter
What are the three criteria for a neurotransmitter?
- 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
What are the steps in synaptic transmission?
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
T or F. Under most conditions, membrane potential changes occur only with significant change in ion concentration.
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+
Electrical signaling often results in a ____ influx to transduce the electrical signal into other biochemical signals.
Where are Ca2+ channels position in the pre-synaptic bouton?
Directly below the active zone
What machinery in the synapses is a target of bacterial toxins?
T or F. Vesicles are destroyed after releasing neurotransmitter.
FALSE - they are recycled and reused
What is channel gating?
Conformational changes that affect channel open probability
What are 4 common gating mechanisms?
2. Ligand-gated (extracellular molecule)
3. Signal-gated (intracellular molecule)
What are the main receptors found at excitatory synapses? What type of ion do they allow to pass through the channel?
Ionotrophic glutamate receptors
Opening of the glutamate receptor channel is near 0 mV so opening it drives membrane potential to _____ (depolarize/hyperpolarize)
_____ ensures that ionic currents will go to 0 if conductance is kept constant.
System attractor point
____ shift system attractor point toward channel's 0 current potential if conductance is _____ or away if conductance is _____
Channel conductance changes
Are glutamate receptors open or closed at rest? Why?
Closed - because opening it requires a torqued conformation which is not energetically favorable
Ligand binding to glutamate receptors only stabilizes the _____ state (activated or closed)
Where is glycine primarily used as a neurotransmitter? Is it excitatory or inhibitory
Spinal cord - inhibitory
Excitatory sites primarily use ____ channels, while inhibitory sites primarily use ____ channels
Where in the neuron are synaptic responses generated? Where are action potentials produced?
Soma and hillock
For sustained current injections, the signals decay exponentially with distance with a characteristic _______
For passive spread of signals in neurons, _____ membrane resistance and _____ axial resistance increase the space constant
For transient current injections, the signals decay even faster with distance due to _____
charging of the membrane capacitance
What are complicating factors for signal propagatino?
- Varying dendritic branch diameters
- Varying distance of inputs from the soma
- Voltage-gated channels that reshape basic synaptic responses
T or F. An action potential can be generated with a single synaptic event.
FALSE - many small synaptic events must sum together to reach threshold
Simultaneous stimulation of two connections
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
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
Repetitive stimulation of same connection
What is rate limiting step for response termination?
Elimination of transmitters within synaptic cleft or for higher affinity receptors, neurotransmitter unbinding from receptor
Temporal summation is ____ (linear/sub-linear)
If receptor population is overlapping, there will be competition between transmitters for the same receptors, producing ____(linear or sub-linear) summation.