Neural Communication

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Neural Communication
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Electrochemical Signaling
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Key Terms

• Ion - a charged chemical element
• Electric currents - carried by movements of ions
  across membrane of cells
• Potential - a force created when ions of opposite
  charge are separated

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Ions In and Around Neurons

• Important Ions!
• Na
• K
• Cl-
• Ca2
• Proteins-

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Movement of Ions Influenced by...

• Concentration gradient
• Electrical Forces

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CONCENTRATION GRADIENT

• Difference in concentration of a substance
  between 2 locations

A substance will move from an area of high
concentration to low
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Electrical Forces
LIKE REPELS LIKE
OPPOSITES ATTRACT
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To understand electrical properties of neurons,
lets look at a resting neuron, one that is NOT
transmitting a signal.
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Resting Potential (RP)
see fig 4.10
RP - produced by unequal distribution of ions
between inside outside of neuron
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What is the basis of the RP?

• Distribution of ions
• Na (sodium)
• K (potassium)
• Cl- (chloride)
• An- (other anions)

This uneven distribution sets up concentration
and electrical gradients
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Selective Permeability - due to ion channels

• Distribution of ions
• Na (sodium)
• K (potassium)
• Cl- (chloride)
• An- (other anions)

Na
K
Na
K
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Basis of the RP
Fig 4.10

• Selective permeability
• Concentration gradients
• Electrical gradients
• Sodium-Potassium Pump (Na/K)

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Resting Potential Generation

• Na/K Pump active
• Na channels closed
• K channels open

Na is poised to RUSH in! Thus, RP provides
an ENERGY STORE
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HYPERPOLARIZATION
Fig 4.11
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DEPOLARIZATION
Fig 4.11
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Action Potential

• Active excited firing
• Stereotyped massive depolarization
• Fundamental signaling unit within neuron
• Basis of long-distance signaling

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Action Potential

• Threshold of Excitation
• All-or-none
• Voltage-sensitive channels
• Refractory Period
• Absolute
• Relative

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Action Potential
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Initiation of AP at Axon Hillock
The Soma does not have many voltage sensitive
channels. The Axon hillock has a high density of
them.
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Propagation of Action Potential
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Saltatory Conduction

• Node of Ranvier
• No myelin
• High density of voltage-sensitive channels
• Electrical insulation speeds AP from node to node

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Saltatory Conduction
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• TTX made from bacteria
• Bocks Na channels
• Death in about 6 hrs
• Tingling, numbness in lips tongue
• Face throat
• Salivation, sweating
• Heart rate temp. drop
• Respiratory distress
• Paralysis convulsion
• Doesnt cross BBB
• No antidote

The Puffer Fish
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• What causes a neuron to fire?
• How are signals transmitted from one neuron to
  another?

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How is AP triggered?
Synaptic inputs ? Postsynaptic Potentials
Threshold
Sum ? Threshold ? Action Potential
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Multiple Synaptic Inputs
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Summation of Synaptic Potentials