PSB 3002 Exam 2 Review Questions
with Complete Answers
How do the ions pass through the cell membrane? - ANSWER-ions are hydrophilic,
so they cannot easily cross the hydrophobic part of the membrane (tails). they must
be facilitated through the membrane with the help of transmembrane proteins which
are like pores that allow ions to pass through (such as ion channels).
What is the all-or-none law? - ANSWER-an action potential either occurs, or does
not occur; once initiated, is always transmitted down the axon at the same size
Explain how the presence of myelin on an axon speeds up conduction velocity. What
is this form of conduction called? - ANSWER-called *saltatory conduction*; myelin
sheaths create gaps (called nodes of ranvier). instead of having ion channels along
the whole axon, ion channels are ONLY at those nodes. that means that ion
channels do not need to wait for the adjacent ion channel to open and create an
action potential in order to trigger the opening of the next. instead, the conduction
remains depolarized to the threshold while traveling under myelin sheath
(decremental conduction). once it reaches the node of ranvier then, it can trigger the
opening of ion channels + an action potential at that node, rather than along the
length of the whole axon
Describe the events that take place at the axon terminal from the time an action
potential arrives to the time neurotransmitter is released into the synapse. -
ANSWER-1.) vesicles containing NT dock against the presynaptic membrane
(proteins on the vesicle bind with proteins on the membrane)
2.) action potential comes along terminal buttons; if depolarized to a certain point,
calcium channels will open, and calcium will enter the cell.
3.) calcium binds with docking proteins on the presynaptic membrane, bringing about
the fusion of the vesicles to the membrane to release NT.
Contrast ionotropic and metabotropic receptors. - ANSWER-*ionotropic:* direct
action on ion channels; binding of the appropriate neurotransmitter opens ion
channels
*metabotropic:* indirect method of opening ion channels; a ligand binding to
receptors start a chain of chemical events:
1.) binding activates a G protein
2.) G protein activates an enzyme that stimulates a second messenger
3.) the second messenger travels to nearby ion channels to open them
, Define (a) depolarization (b) hyperpolarization (c) EPSP (d) IPSP. - ANSWER-a.)
depolarization: inside of the cell becomes more positive
b.) hyperpolarization: inside becomes more negative
c.) EPSP: excitatory postsynaptic potential; depolarization of a postsynaptic cell due
to the opening of sodium channels (influx of Na+ and Ca^2+)
d.) IPSP: inhibitory postsynaptic potential; a hyperpolarization of the postsynaptic
membrane caused by the opening of potassium (K+ efflux), and/or chloride channels
(Cl- influx)
postsynaptic potential - ANSWER-the change in the membrane potential of a neuron
that has received stimulation from the presynaptic neuron; either increases or
decreases the firing rate of the postsynaptic axon (inhibitory = IPSP, or excitatory =
EPSP)
Describe two mechanisms for terminating the effects of the neurotransmitter after it
has been released into the synaptic cleft. - ANSWER-1.) *reuptake:* rapid removal of
neurotransmitter from the synaptic cleft by the terminal button; neurotransmitter is
released when an action potential arrives, then transported back into the presynaptic
terminal, giving the postsynaptic receptors brief exposure to the neurotransmitter
2.) *enzymatic deactivation:* an enzyme destroys the neurotransmitter in the
synapse; ex. acetylcholine by acetylcholinesterase
Describe the five stages of the life cycle of a neurotransmitter. - ANSWER-1.)
synthesis: precursors and enzymes
2.) storage in synaptic vesicles for transport down the presynaptic cell
3.) release of the neurotransmitter from presynaptic terminal; when action potential
arrives at axon terminal, it brings about the fusion of the vesicles w/ the membrane
4.) binding to a receptor on postsynaptic cell; brings about excitatory response
(EPSP or IPSP in the postsynaptic cell)
5. inactivation; enzymes or reuptake
Outline the synthesis of acetylcholine, including all substrates and enzymes. -
ANSWER-precursors: choline & acetyl coenzyme A
enzyme: choline acetyltransferase (ChAT)
ChAT transfers the acetate ion from acetyl coenzyme A to choline, forming
acetylcholine
Name a drug that (a) blocks and (b) stimulates the release of ACh. - ANSWER-a.)
*botulinum toxins, botox, atrophine, and curare* block the release of ACh
with Complete Answers
How do the ions pass through the cell membrane? - ANSWER-ions are hydrophilic,
so they cannot easily cross the hydrophobic part of the membrane (tails). they must
be facilitated through the membrane with the help of transmembrane proteins which
are like pores that allow ions to pass through (such as ion channels).
What is the all-or-none law? - ANSWER-an action potential either occurs, or does
not occur; once initiated, is always transmitted down the axon at the same size
Explain how the presence of myelin on an axon speeds up conduction velocity. What
is this form of conduction called? - ANSWER-called *saltatory conduction*; myelin
sheaths create gaps (called nodes of ranvier). instead of having ion channels along
the whole axon, ion channels are ONLY at those nodes. that means that ion
channels do not need to wait for the adjacent ion channel to open and create an
action potential in order to trigger the opening of the next. instead, the conduction
remains depolarized to the threshold while traveling under myelin sheath
(decremental conduction). once it reaches the node of ranvier then, it can trigger the
opening of ion channels + an action potential at that node, rather than along the
length of the whole axon
Describe the events that take place at the axon terminal from the time an action
potential arrives to the time neurotransmitter is released into the synapse. -
ANSWER-1.) vesicles containing NT dock against the presynaptic membrane
(proteins on the vesicle bind with proteins on the membrane)
2.) action potential comes along terminal buttons; if depolarized to a certain point,
calcium channels will open, and calcium will enter the cell.
3.) calcium binds with docking proteins on the presynaptic membrane, bringing about
the fusion of the vesicles to the membrane to release NT.
Contrast ionotropic and metabotropic receptors. - ANSWER-*ionotropic:* direct
action on ion channels; binding of the appropriate neurotransmitter opens ion
channels
*metabotropic:* indirect method of opening ion channels; a ligand binding to
receptors start a chain of chemical events:
1.) binding activates a G protein
2.) G protein activates an enzyme that stimulates a second messenger
3.) the second messenger travels to nearby ion channels to open them
, Define (a) depolarization (b) hyperpolarization (c) EPSP (d) IPSP. - ANSWER-a.)
depolarization: inside of the cell becomes more positive
b.) hyperpolarization: inside becomes more negative
c.) EPSP: excitatory postsynaptic potential; depolarization of a postsynaptic cell due
to the opening of sodium channels (influx of Na+ and Ca^2+)
d.) IPSP: inhibitory postsynaptic potential; a hyperpolarization of the postsynaptic
membrane caused by the opening of potassium (K+ efflux), and/or chloride channels
(Cl- influx)
postsynaptic potential - ANSWER-the change in the membrane potential of a neuron
that has received stimulation from the presynaptic neuron; either increases or
decreases the firing rate of the postsynaptic axon (inhibitory = IPSP, or excitatory =
EPSP)
Describe two mechanisms for terminating the effects of the neurotransmitter after it
has been released into the synaptic cleft. - ANSWER-1.) *reuptake:* rapid removal of
neurotransmitter from the synaptic cleft by the terminal button; neurotransmitter is
released when an action potential arrives, then transported back into the presynaptic
terminal, giving the postsynaptic receptors brief exposure to the neurotransmitter
2.) *enzymatic deactivation:* an enzyme destroys the neurotransmitter in the
synapse; ex. acetylcholine by acetylcholinesterase
Describe the five stages of the life cycle of a neurotransmitter. - ANSWER-1.)
synthesis: precursors and enzymes
2.) storage in synaptic vesicles for transport down the presynaptic cell
3.) release of the neurotransmitter from presynaptic terminal; when action potential
arrives at axon terminal, it brings about the fusion of the vesicles w/ the membrane
4.) binding to a receptor on postsynaptic cell; brings about excitatory response
(EPSP or IPSP in the postsynaptic cell)
5. inactivation; enzymes or reuptake
Outline the synthesis of acetylcholine, including all substrates and enzymes. -
ANSWER-precursors: choline & acetyl coenzyme A
enzyme: choline acetyltransferase (ChAT)
ChAT transfers the acetate ion from acetyl coenzyme A to choline, forming
acetylcholine
Name a drug that (a) blocks and (b) stimulates the release of ACh. - ANSWER-a.)
*botulinum toxins, botox, atrophine, and curare* block the release of ACh
