The Nervous System
Group: Julia, Lexie, Sean, Brianna
Remember these terms...
Chemical Synapses
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The narrow cleft between the
presynaptic cell and the postsynaptic
cell
Specialized junctions through which
neurons signal to:
o each other
o non-neuronal cells (such as those
in muscles or glands)
Chemical synapses allow neurons to
form circuits within the central nervous
system.
They are crucial to the biological
computations that underlie perception
and thought.
Axon Terminal
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Enlarged region located at the end of a
neuron’s axon
Separated from the next cell by a small
gap (synaptic cleft)
Action Potential
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An electrical signal that is a fleeting
reversal in the voltage difference across
a neuron’s plasma membrane.
NEW TERMS
● Presynaptic cell
● Postsynaptic cell
● Neurotransmitters
How do chemical synapses work?
● When action potential reaches the axon terminal of the presynaptic cell, voltage
gated calcium ion channels are opened.
● Calcium ions in these channels flow down their concentration gradient, from
outside of the cell to inside the cell
● This flow induces the synaptic vesicles (containing neurotransmitters) to fuse
with the plasma membrane and release the neurotransmitters from the axon
terminal (via exocytosis) into the synaptic cleft.
● Note: the action potential is an electrical signal, and cannot cross the synaptic
cleft for it would dissipate, so it is converted to a chemical signal in the form of
neurotransmitters
How do neurotransmitters work?
● After crossing the synaptic cleft, neurotransmitters bind to receptor molecules on
the postsynaptic cell. This binding changes the receptors shape and creates a
passageway through its interior for the neurotransmitters to enter the cell.
● The neurotransmitters, once in the cell, either stimulate the receptor cell to form a
new action potential by opening a sodium channel, or inhibit the cell from forming
an action potential when stimulated by another neuron
● This is what is called the excitatory and inhibitory effect.
o excitatory effect: whether a neurotransmitter will help drive the postsynaptic
cell to form an action potential
o inhibitory effect: whether a neurotransmitter will prevent the postsynaptic cell
to form an action potential
Examples of Neurotransmitters
● Dopamine
o Both a hormone and a neurotransmitter, acts as a NT in
the brain
o Diseases like Parkinson’s and Schizophrenia are
associated with dysfunctions of the dopamine system
o Inhibitory neurotransmitter - blocks action potentials
o Strongly associated with reward mechanisms in the brain
o Drugs like cocaine, nicotine, and alcohol increase
dopamine levels2
Examples of Neurotransmitters
● Acetylcholine (ACh):
o acts at chemical synapses between a motor neuron and
muscle cell
o ACh is released from the motor neuron, diffuses across
the cleft, and binds to the receptors on the muscle cell
membrane
o In this kind of cell it has excitatory effects (trigger action
potentials) which in turn initiate muscle contraction
Bibliography
1. Starr, Cecie, Ralph Taggart, and Lisa Starr. Biology: The Unity and Diversity of Life. Australia:
Brooks/Cole, 2001. Print.
1. Boeree, George C., Dr. "Neurotransmitters." Webspace.ship.edu. N.p., 2003. Web. 17 Nov.
2014.
1. Taylor, Tim. "Nervous System." InnerBody. InnerBody, 1999. Web. 16 Nov. 2014.
1. "What Are Neurotransmitters?" What Are Neurotransmitters? Neurogistics, 2014. Web. 15 Nov.
2014.