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Problem Set #5
Due on Oct. 15, 2005
Name: ________________________
1) Match the following traces with the correct term. (1 point)
1. c;
1. Synaptic Depression ________
2. Temporal Summation ________
3. IPSP _________
4. EPSP _________
5. Synaptic Facilitation ________
2. e; 3. d; 4. a;
5. e.
2a) Draw a diagram showing 3 neurons arranged in a circuit where presynaptic facilitation
takes place. Label the diagram, and explain how presynaptic facilitation occurs. (1 point)
b)
How does presynaptic facilitation differ from facilitation due to repetitive stimulation
at a single synapse? (1 point)
Facilitation from repetitive stimulation (aka normal facilitation) involves only two cells (1
presynaptic and 1 postsynaptic cell). The increase in EPSP occurs because there is a buildup
of Ca in the presynaptic terminal b/c multiple APs end at the presynapse within a small
amount of time. More Ca = more neurotransmitters released = greater EPSP.
Presynaptic facilitation involves three cells (1 presynaptic, 1 post synaptic and 1
prepresynaptic (synapses on presynaptic terminal). The increase in EPSP occurs b/c more
Ca++ channels open in the presynaptic terminal b/c the prepresynaptic cell lengthens the
depolarization at the presynaptic terminal (longer depolarization = more Ca channels open =
more neurotransmitters are released).
c)
How does facilitation at a single synapse differ from LTP? (1 point)
Facilitation is a short-term process that results from presynaptic changes in Ca++. LTP is
long-term in nature (hours to days) and results from postsynaptic events (e.g. insertion of
AMPA receptors into membrane).
3) Name two types of ionotropic glutamate receptors and describe differences between the
two. (1 point)
NMDA receptors and AMPA receptors. AMPA receptors are readily opened by ligand
glutamate; but in the presence of glutamate, NMDA receptor channels are open only during
depolarization b/c these channels are blocked by Mg++ at resting potentials.
4) Please refer to the paper discussed in the class (Rumpel et al., Science 308: 83-88) and
answer the following questions.
a) What region of the brain did the authors choose to study and why? (0.5 point)
Amygdala is deep brain structures related with emotions, especially fear.
b) What is the purpose of infecting neurons with vectors that express GFP only?(0.5 point)
As the control for infection of cells with virus.
c) What vector was used to illustrate that new AMPA glutamate receptors were inserted into
the postsynaptic membrane during LTP, and how did these new AMPA receptors
functionally differ from the endogenous ones already present in the synapse? (1 point)
The authors used the vector containing the GluR1 fused with GFP. These new AMPA
receptors displayed greater rectification.
5) Some forms of Long QT Syndrome are dominant-negative mutations because: (1 point)
a. Mutant potassium channel subunits form heteromultimers with wild-type subunits, and
these heteromultimers are nonfunctional.
b. The mutant potassium channel gene suppresses the genetic expression of the cardiac
sodium channel.
c. The mutation in the potassium channel gene is recessive.
d. The mutant potassium channel shortens the duration of the cardiac action potential.
e. None of the above.
6a) When a neurotransmitter molecule is released from presynaptic cell, what are the three
things that could possibly happen to the neurotransmitter? (1 points)
1) Bound to receptors at postsynaptic membrane.
2) Reuptaken to presynaptic cell and glia cells.
3) Degraded.
b) During reuptake of neurotransmitters, where do the neurotransmitters go? (1 point)
a. Across the synapse and into the postsynaptic neuron
b. Remain in the extracellular medium.
c. Into the presynaptic neuron and adjacent glia cells
d. Into the mitochondria
SCORE:
_____/10