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Dr. Martin Shapiro's Neuron Communication Lecture - Part of Dr. Isom's Psych 36 class at California State University, Fresno.
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Neurons Communication: An Electrochemical and Chemical Process
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Sodium ChlorineChloride
Na+ Cl-
-
electrons
protons
Membrane Potential
• The inside of the cell has a negative charge compared with the outside.
• The membrane has a polarity.• This is maintained by pumping positive
charged ions (Na+) outside.
A-A-
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Extracellular
Intracellular
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5-70
mV
Changing the Polarity
• Resting potential: (-70 mV): The membrane potential of a neuron when it’s not being affected by other neurons.
• Depolarization: reducing the polarity of the neuron. Moving from -70 mV towards zero. Adding more positively charged ions into the cell or removing negatively charged ions from the inside.
• Hyperpolarization: Increasing the polarity of the membrane.
Ion Channels
How do ion channels open or close?
• Voltage-dependant ion channel (voltage-gated): When the membrane around the channel reaches a specific polarity it will open.
• Chemical-dependant ion channel (chemical-gated): A chemical, such as a neurotransmitter, causes it to close or open.
Chemical-Gated Ion ChannelVoltage-Gated Ion Channels
Na+
Na+
Na+
Na+
A-
A-
A-
A-
A-
A-
A-
A-
A-A-
Na+Na+
Na+
Na+
K+
K+ K+ K+
K+
K+
K+
K+
Na+
Na+ Na+Na+
Na+
Na+Na+
Na+
Na+
Na+
K+
K+ K+
Neurotransmitter
Na+ Na+
Na+
Na+Na+
Na+
A-
A-
A-
Voltage-Gated Ion ChannelsDepolarization
Na+
Na+
Na+
Na+Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
A-
A-
A-
A-
A-
A-
A-
A-
A-A-
Na+
Na+
Na+Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+ K+ K+
K+
K+
K+
Voltage Inside-70 mVResting
K+
K+
K+
Na+
Na+
Na+
Na+
Threshold-65 mV
K+ K+ K+
Propagation of the Action Potential
Inside the Axon
Myelin
Node of Ranvier
Depolarization
Action Potential
Depolarization Na+ Repolarization Potassium K+
Na+
Na+Na+
Na+
K+
K+
K+
K+
Action Potential
Time
mV
+40
0
-65
-70
Na+
Channelsopen
K+
Channelsopen
Na+
Channelsclose
K+ Channelsstay open
ThresholdPotential
RestingPotential
K+ ChannelsClose
Depolarization followed by repolarization
Inside the Axon
Myelin
Node of Ranvier
Action Potential
Action Potential
• Depolarization– A stimulus causes a gate in the Na+ Channel to
open. Since there is a high concentration of Na+ outside, Na+ diffuses into the neuron. The electrical potential changes to ~ +40 mV.
• Repolarization– Depolarization causes the K+ Channel gate to
immediately open. K+ diffuses out of the neuron. This reestablishes the initial electrical potential of ~ -70 mV.
Sodium-Potassium Pump
A P PPNa+
Na+
Na+
K+K+
ATPADP
K+
K+
K+K+
K+
K+
K+
K+
Na+
Na+
Na+Na+
Na+
A-
A-
A-
A-
Synapse
Synapse
Synaptic Cleft
Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
Action potential
• The depolarization at one spot caused a depolarization at a spot further down the axon.
• Boom boom boom!
Neurotransmitters
• Neurotransmitters: Chemicals produced by a neuron that are sent across the synapse to affect a post-synaptic cell by binding to a receptor.
• The neurotransmitter fits a receptor like a specific key to a lock.
Synapse
Synaptic Cleft
Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
Chemical-Gated Ion ChannelVoltage-Gated Ion Channels
Na+
Na+
Na+
Na+
A-
A-
A-
A-
A-
A-
A-
A-
A-A-
Na+Na+
Na+
Na+
K+
K+ K+ K+
K+
K+
K+
K+
Na+
Na+ Na+Na+
Na+
Na+Na+
Na+
Na+
Na+
K+
K+ K+
Neurotransmitter
Na+ Na+
Na+
Na+Na+
Na+
A-
A-
A-
SynapseTransporterCa++
Ca++
Ca++
Ca++
Ca++
Ca++
Neurotransmitters
• Excitatory (Excitation): Increases the likelihood of producing an action potential on the post-synaptic cell.– Glutamate, dopamine, norepinephrine,
epinephrine• Inhibitory (inhibition): Decreases the
likelihood of producing an action potential on the post-synaptic cell.– GABA, 5-HT, dopamine, substance p
Psychopharmacology
• antagonist–A drug that opposes or inhibits the effects of
a particular neurotransmitter on the postsynaptic cell.
• agonist–A drug that facilitates the effects of a
particular neurotransmitter on the postsynaptic cell.
