Download Chemical Synapses activity and project

Name _________________________________________________
Modeling Chemical Synapses
A synapse is the place where signals are transmitted from a neuron, the presynaptic neuron, to
another cell. This second cell may be another neuron, muscle cell or glandular cell. If the second cell
is a neuron, it is called the postsynaptic neuron.
The majority of synapses are chemical synapses which function by releasing a chemical called a
neurotransmitter from the presynaptic neuron. Over 50 different neurotransmitters have been
identified with another 50 suspected of being neurotransmitters. These neurotransmitters act to excite
or inhibit postsynaptic cells by binding to specific receptor proteins embedded in the postsynaptic cell.
Depending on the receptor, the same neurotransmitter may have excitatory effects at some
synapses while having inhibitory effects at others. For example, acetylcholine excites skeletal muscle
cells but inhibits cardiac muscle cells.
In this simulation you will determine how excitatory and inhibitory neurotransmitters alter the
release of dopamine from the last neuron in a series.
Using your computer or your textbook, complete the following table.
Neurotransmitter
Role in the body
acetylcholine
dopamine
GABA
(gamma-aminobutyric
acid)
glutamate
norepinephrine
serotonin
Operation of the nervous system is dependent on the flow of information through chains of neurons
functionally connected by synapses. The neuron conducting impulses toward the synapse is the presynaptic
neuron, and the neuron transmitting the signal away from the synapse is the postsynaptic neuron. Chemical
synapses are specialized for release and reception of chemical neurotransmitters. For the most part,
neurotransmitter receptors in the membrane of the postsynaptic cell are either 1.) channel-linked receptors,
which mediate fast synaptic transmission, or 2.) G protein-linked receptors, which oversee slow synaptic
responses. Channel-linked receptors are ligand-gated ion channels that interact directly with a
neurotransmitter and are called ionotropic receptors. Alternatively, metabotropic receptors do not have a
channel that opens or closes but rather, are linked to a G-protein. Once the neurotransmitter binds to the
metabotropic receptor, the receptor activates the G-protein which, in turn, goes on to activate another
molecule.
Part 1 – Cholinergic Synapse
Model the ionotropic cholinergic synapse shown below. Be sure to label all of the following:
voltage-gated sodium channel, voltage-gated potassium channel, neurotransmitter, synaptic vesicle,
presynaptic cell, postsynaptic cell, potassium leaky channel, sodium-potassium pump, synaptic cleft,
acetylcholine receptor, acetylcholinesterase, calcium channel, SNARE proteins.
Step 1 - Action potential arrives at the terminal end of the
presynaptic cell.
Step 2 - Calcium channels open in the
presynaptic axon terminal. Open the
calcium channels (red) and move some
calcium ions to the interior of the neuron.
Calcium ions bind to synaptotagmin.
Step 3 - SNAP/SNARE proteins interact to bring the
vesicle in position to fuse with the cell membrane.
Acetylcholine is released. Move the synaptic vesicle to the
terminal end of the neuron.
Step 5 - Ion channels open in the postsynaptic
membrane. The acetylcholine receptor opens to
allow sodium ions to follow their concentration
gradient into the postsynaptic cell. Depolarization of
the postsynaptic cell occurs and an action potential
may be generated in the post synaptic cell.
Step 4 - Acetylcholine binds to postsynaptic
receptors. Acetylcholine traverses the synaptic cleft
to bind to the acetylcholine receptor on the
postsynaptic membrane.
Step 6 - Termination of acetylcholine effects. The
enzyme acetylcholinesterase breaks the
neurotransmitter down into acetic acid and choline.
An uptake receptor transports choline back into the
presynaptic cell for use in the synthesis of more
acetylcholine in the presynaptic cell.
Learning Check:
A. Identify the ion that triggers the SNAP/SNARE proteins to cause the synaptic vesicle to “kiss and
run”. ____________
B. What molecule is released into the synaptic cleft in this model? _________________________
C. Why is it important that acetylcholinesterase is present in the synaptic cleft? ________________
_______________________________________________________________________________
D. What happens in the post synaptic cell when acetylcholine binds to the receptor? ____________
_______________________________________________________________________________
E. Identify the cholinergic synapse modeled here as excitatory or inhibitory. Explain your choice.
________________________________________________________________________________
F. Brainstorm ways in which the transmission in a cholinergic synapse could go wrong.
1. _________________________________________________________________________
2. _________________________________________________________________________
3. _________________________________________________________________________
Part 2 – Dopaminergic Synapse
Model the metabotropic dopaminergic synapse shown below. Be sure to label all of the following:
voltage-gated sodium channel, voltage-gated potassium channel, dopamine, synaptic vesicle,
presynaptic cell, postsynaptic cell, potassium leaky channel, sodium-potassium pump, synaptic cleft,
G-protein coupled receptor, calcium channel, dopamine transporter, vesicular transporter,
SNAP/SNARE proteins.
Repeat steps 1-3 as before, but use dopamine as the NT.
Step 4 - Dopamine traverses the synaptic cleft to
bind to the extracellular domain of the metabotropic
receptor in the postsynaptic membrane. The
intracellular domain of the metabotropic receptor
binds to G-proteins. The G-protein has three
subunits: alpha(α), beta(β), and gamma(γ).
Step 5 - Bound dopamine activates the
metabotropic receptor. The α subunit dissociates
from the βγ complex. The α subunit triggers a signal
cascade that ends in the opening of ion channels,
depolarizing the postsynaptic cell.
Step 6 - The effects of dopamine are terminated
when dopamine is removed from the synaptic cleft
by the dopamine uptake transporter and returned to
the vesicle.
Learning Check:
A. Identify the dopaminergic synapse modeled here as excitatory or inhibitory. Explain.
______________________________________________________________________________
B. Describe how an ionotropic receptor differs from a metabotropic receptor.
______________________________________________________________________________
______________________________________________________________________________
C. Brainstorm ways in which the dopaminergic synapse transmission could go wrong.
1. ______________________________________________________________________
2. _______________________________________________________________________
3. _______________________________________________________________________
Let’s look at a case study of the Beery Twins – dopamine deficiency
Part 3 – GABAergic Synapse
Model the GABAergic synapse shown below. Be sure to label all of the following: voltage-gated
sodium channel, voltage-gated potassium channel, GABA, synaptic vesicle, presynaptic cell,
postsynaptic cell, potassium leaky channel, sodium-potassium pump, synaptic cleft, GABA receptor,
calcium channel, SNAP/SNARE proteins.
Model steps 1-4 as you did with the cholinergic synapse, but use GABA as the NT.
Step 5 - Ion channels open in the postsynaptic
membrane. The GABA receptor opens to allow
chloride ions (Cl-) to follow their concentration
gradient into the postsynaptic cell. Hyperpolarization
of the postsynaptic cell occurs inhibiting the
generation of an action potential.
Step 6 - High-affinity transporters terminate the action
of GABA by returning it to the presynaptic neuron for
reuse.
Learning Check:
A. Identify the GABAergic synapse as ionotropic or metabotropic. Explain.
______________________________________________________________________________
B. Why is the GABAergic synapse considered inhibitory? _________________________________
_______________________________________________________________________________
Project due date __________________________________
Each table will be assigned a different drug that somehow interferes with synaptic transmission. Your
job is to research the drug’s action on the neurons/synapses and the long-term effects, create a
model using the appropriate synapse type from the Synapse Kit.
Drugs to choose from: caffeine, tetanus toxin, methamphetamines, cocaine, sarin gas, alcohol,
or propofol (Diprivan)
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Construct your own “informational placemat” that explains the normal vs. the drug effects at
the synapse level and the effects on body systems. Use your own photographs of your model
and others on your placemat.
If time permits, your group will present your model and drug effects to the class.