Name ____________________
biol 125 homework 3
Part 1: Multiple choice
1. Glutamate is
A. the most commonly used neurotransmitter in the brain
B. can cause excitotoxicity at high concentrations
C. a nonessential amino acid
D. often synthesized from glial-provided glutamine
E. All of the above <–––
2. The presence of which of the following compounds or proteins in a cell makes it quite likely that the cell is a GABAergic
neuron?
A. Pyridoxal phosphate
B. Glutamic acid decarboxylase <–––
C. GABA transaminase
D. γ-hydroxybutyrate
E. Glutamine
3. Serotonin reuptake blockers such as fluoxetine (Prozac) are used clinically
A. to treat hypertension
B. to treat panic disorders
C. as antidepressants <–––
D. as antipsychotics
E. to treat generalized anxiety
4. In terms of molecular size, which of the following are the largest neurotransmitters?
A. Biogenic amines
B. Amino acid transmitters
C. Neuropeptide transmitters <–––
D. Purinergic transmitters
E. Gaseous transmitters
5. Peptide neurotransmitters are often released
A. shortly after their synthesis in presynaptic terminals
B. as pre-propeptides
C. as propeptides
D. more readily and quickly than nonpeptide transmitters
E. together with nonpeptide transmitters <–––
6. The acetylcholine receptor at the skeletal neuromuscular junction would best be described as a(n)
A. ionotropic receptor <–––
B. metabotropic receptor
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biol 125 homework 3
C. G-protein-coupled receptor
D. nuclear receptor
E. gap junction
7. The reversal potential of acetylcholine receptor channels is close to zero because:
A. Opening of the channel at any given voltage leads to zero current flow
B. Opening of the channel at resting membrane potential leads to zero current flow
C. The channel is a non-selective monovalent cation channel, so the reversal potential is somewhere in between the
Dquilibrium potential for potassium and sodium <––
E. The channel is selectively permeable to potassium, whose equilibrium potential is very close to zero
E. The equilbrium potential for sodium is greater than the action potential threshold
8. The most important factor determining whether an ionotropic neurotransmitter receptor is inhibitory or excitatory is
A. the ligand-binding properties of the receptor
B. whether the permeant ion is positively or negatively charged
C. whether the permeant ion’s reversal potential is positive or negative
D. whether the permeant ion’s reversal potential is positive or negative to threshold <–––
E. None of the above
9. Which of the following statements about postsynaptic currents at the neuromuscular end plate is false?
A. Depolarizing currents can be recorded from outside–out patches of postsynaptic membrane
B. Individual channels tend to stay open for no more than a few msec
C. Acetylcholine can induce openings of ligand-gated ion channels
D. The end plate potential is due to the opening of thousands or millions of channels
E. The end plate channels show a regenerative opening pattern that propagates an action potential along the length of the
muscle fiber <–––
10. A cell contains the precursors tyrosine and dihydroxyphenylalanine (DOPA) and the enzymes tyrosine hydroxylase and DOPA
decarboxylase but not dopamine-!-hydroxylase. Which of the following neurotransmitters will it synthesize?
A. serotonin
B. dopamine <–––
C. norepinephrine
D. epinephrine
E. More than one of the above are true
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Name ____________________
biol 125 homework 3
Part 2: Short answers
1. Give examples of neurotransmitters in each of the following categories:
Purinergic: ATP, AMP, adenosine
Biogenic amine: Catecholamines (Dopamine, Norepinephrine, Epinephrine), Histamine, Serotonin
Amino acid: Glutamate, Glycine, GABA
Peptide: Substance P (brain/gut); β-Endorphin, Met-enkephalin (opioid); vasopressin, oxytocin (pituitary); somatostatin
(hypothalamus), angiotensin, neuropeptide Y (misc)
2. What are the two major inhibitory neurotransmitters in the central nervous system?
GABA and Glycine
2+
3. Why is it so important to keep Ca
Ca
2+
levels low inside the cell, and how is this accomplished?
must be kept at low levels because it acts as a second messenger for many intracellular signaling pathways. Signaling
must be regulated carefully so that the cell only generates responses when the appropriate signal has been detected. Low
2+
intracellular Ca
+2
concentrations are maintained through the use of: (1) Ca
+2
pumps (hydrolyze ATP to pump Ca
+
concentration gradient, can pump out of the cell or into endoplasmic reticulum) (2) Na / Ca
+
+2
energy from Na flowing down its concentration gradient to the flow of Ca
+2
against its
exchangers (couples the
against its concentration gradient)
4. Fill in the blank with A, B, or A+B based on whether the following statements are referring: A= Ionotropic receptors, B=
Metabotropic receptors
___ A Blocked by alpha-bungarotoxin
___ A+B Activation can lead to an EPSP.
___ B Slowest
___ B Their Neurotransmitters are encoded directly by genes.
___ A Picrotoxin and Barbituate binding
___ B Uses a signal transduction signaling mechanism
___ A+B Uses small, clear core vesicles
___ B Catecholamine receptors
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Name ____________________
biol 125 homework 3
Part 3: Short answers
You have set up an experimental system where you can record from a neuron at room temperature that receives inputs from four
other neurons as shown below (Fig. 1). You have determined the ion concentrations inside and outside the cell. Inside: 10 mM
+
–
+
+
–
+
Na 10 mM Cl 100 mM K outside: 100 mM Na 100 mM Cl and 10 mM K . The resting potential for this neuron is –58 mV and
the threshold potential for this neuron is –40 mV.
Fig. 1
Your first experiment is to identify the type of neurotransmitter used at each synapse. To do this you stimulate each presynaptic
neuron and measure determine Erev at each synapse.
1. What is the definition of Erev? How does one experimentally determine Erev?
The reversal potential (Erev) is defined as the membrane potential at which there is no net current flow of the permeable ions.
Voltage clamp experiments can be done to determine Erev. Different voltage steps can be applied to the postsynaptic neuron
while stimulating the presynaptic neurons and Erev will be the voltage at which the current is at 0.
2. You find that Erev for both synapses 1 and 3 is 0 mV. For 2 it is –60 mV and for 4 it is –10 mV. Based on this information
which ion(s) are most likely to be responsible for the currents generated from stimulation of synapses 1 and which ion(s) are
responsible for the currents generated at synapse 2? Which of the connections are excitatory, which are inhibitory?
+
+
+
-
ENa = 58 mV, EK = -58 mV, ECl = -58 mV. Synapse 1: Both Na and K , Synapse 2: K or Cl , Synapse 1, 3 and 4 are
excitatory as their Erev are more positive than threshold. Synapse 2 is inhibitory as its Erev is more negative than threshold
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biol 125 homework 3
3. Using extracellular recording techniques you find that you cannot elicit an action potential in the post-synaptic neuron by
stimulating any one of the input neurons. You then start to stimulate combinations of neurons and you find that there are only
three types of stimuli that can drive a postsynaptic action potential. They are 1+3 and 1+3+4 and 1+2+3+4. All other
combinations fail to do this. Is this unusual? Explain what is happening with one or two sentences.
Not unusual. An individual synapse usually doesn’t generate an EPSP above threshold, but through summation of the
numerous EPSPs from all the synapses connected to the postsynaptic neuron, membrane petential can rise to threshold and
action potentials are generated.
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