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Effects of Excitatory and
Inhibitory Potentials on Action
Potentials
Overview of A Neuron
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Found in brain, spinal cord and nervous system
Electrically excitable
Communicate via electrical and chemical synapses
Made up of a soma (cell body), dendritic tree and an
axon
Axon Properties
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Where action potential is propagated
Contains voltage gated sodium and potassium channels
Resting membrane potential: ~ -65 mV
Action Potential
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Occurs when membrane potential exceeds the threshold
potential
Occurs when Na+ channels are activated (inflow of Na+)
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Causes positive slope of action potential
K+ channels open slightly later (outflow of K+)
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Causes downward slope of action potential
Transmission of Action Potential Across
Synapse
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Pre-synaptic cell action potential releases Ca2+ in the axon terminal
Axon terminal releases vesicles filled with neurotransmitters
 Inhibit or help create an action potential
Excitatory Neurotransmitters:
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Acetylcholine
glutamate
Inhibitory Neurotransmitters:
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GABA
glycine
http://thebrain.mcgill.ca/flash/i/i_01/i_01_m/i_01_m_ana/i_01_m_ana.
html#2
Post Synaptic Potentials
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Excitatory Post
Synaptic Potentials
(EPSP)
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Creates positive
synaptic potential
Positive charged ions
flow in
Allows Na+ into cell
Easier for Action
Potential to fire
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Inhibitory Post
Synaptic Potentials
(IPSP)
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Decreases the
potential of the
membrane
Increases permeability
of K+
K+ flows out of cell
Decreases the chances
of an action potential
Ways to Achieve Action Potential
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Temporal Summation
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One neuron acting on
another
Potential starts before the
previous one ends
Amplitudes of potentials
summate to create larger
potential
Spatial Summation
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Multiple cells provide input
Input is received in
different areas
Input is summated to
create a larger potential
Observations
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Increasing the intensity does not increase
the size of the action potential
Action potential is “all or none” response
Potentials can summate to elicit or inhibit
an action potential
Must reach a specific threshold potential
to create and action potential that will be
propagated
Conclusion
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Many different ways to elicit an action
potential or to inhibit one
Temporal and Spatial Summation allow for
greater complexity in neural networks
This allows for greater complexity in
organisms
neuron can communicate with multiple
neurons > greater efficiency.