How do neurons communicate?

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How do neurons communicate?
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a
b
c
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How do neurons communicate?

• Need to think about this question 2 ways

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How do neurons communicate?

• 1. within neurons
• 2. between neurons-

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Neuron receiving info
Information traveling down neuron
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How do neurons communicate

• within neurons electrically
• between neurons chemically
• Synapse space between neurons

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Ramon Y Cajal

• developed Golgi Stain
• first determined space between neurons
• synapse

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Neurons can exist in one of 3 states

• the resting state
• the active state
• neuron is firing
• action potential
• the refractory state

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How do we know about what is happening in the
neuron?

• giant squid axon

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At rest

• inside of the axon has a slightly negative charge
  relative to outside the axon
• called the membrane potential
• usually around -70mV

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At rest

• inside of the axon has a slightly negative charge
  relative to outside the axon
• called the membrane potential
• why?

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action potential or spike
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Neuron stimulated (either electrically or by
receiving a message

• see depolarization (change from negative inside
  neuron to more positive)

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action potential or spike
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Neuron stimulated (either electrically or by
receiving a message

• see depolarization (change from negative inside
  neuron to more positive)
• threshold if a great enough depolarization
  occurs, an action potential will occur
• action potential very quick milliseconds
• Other terms spike, firing, generating an AP

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action potential or spike
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• Hyperpolarization
• return to negative
• this is the refractory or recovery period

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action potential or spike
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What causes these changes in electrical potential
and the action potential?

• All axons and cells have a membrane
• thin lipid (fat) bilayer
• The membranes have channels (to allow ions in or
  out)
• Ions molecules with a charge
• These channels can be open or shut

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What causes these changes in electrical potential?

• Ions flowing across the membrane causes the
  changes in the potential
• Ions are molecules that contain a positive or
  negative charge
• anion negative charge
• cation positive charge

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Some important ions for neuronal communication

• Na sodium
• HIGHER CONCENTRATION OUTSIDE THE AXON
• Cl- chloride
• HIGHER CONCENTRATION OUTSIDE AXON
• K potassium
• higher concentration inside the axon
• A- anions -large (-) molecules with a negative
  charge (stuck inside the axon)

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OUTSIDE AXON (EXTRACELLULAR FLUID)
INSIDE AXON (intracellular)
Na
Cl-
Na
Cl-
A-
Cl-
Cl-
A-
Cl-
Na
Na
Cl-
Cl-
A-
Na
Na
Na
A-
Na
Cl-
Na
Na
A-
Cl-
Na
Cl-
Cl-
Na
Na
A-
Cl-
Cl-
Cl-
Cl-
Na and Cl- are in higher concentration in the
extracellular fluid
Neuron at Rest
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INSIDE AXON
OUTSIDE AXON (EXTRACELLULAR FLUID)
Cl-
K
K
K
Cl-
A-
Na
Cl-
Na
A-
K
Na
A-
Cl-
Na
A-
K
Na
Cl-
Na
K
K
K and negative anions are in higher
concentration in the intracellular or inside the
axon
Neuron at Rest
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Some forces that play a role in maintaining
membrane potential

• concentration gradient
• ions diffuse from higher concentration to lower
  concentration

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example of concentration forces
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What would each ion do if the ion channel opened
based on the concentration gradient?
Na
K
Cl-
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Some forces that play a role in maintaining
membrane potential

• concentration gradient
• ions diffuse from higher concentration to lower
  concentration
• electrical gradient -
• opposite charges attract so ions are attracted to
  an environment that has a charge that is opposite
  of the charge they carry!

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example of electrostatic forces
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What would each ion do if the ion channel opened
based on electrostatic forces ?
Na
K
Cl-
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OUTSIDE AXON (EXTRACELLULAR FLUID)
INSIDE AXON (intracellular)
Na
Cl-
Na
Cl-
A-
Cl-
Cl-
A-
Cl-
Na
Na
Cl-
Cl-
A-
Na
Na
Na
A-
Na
Cl-
Na
Na
A-
Cl-
Na
Cl-
Cl-
Na
Na
A-
Cl-
Cl-
Cl-
Cl-
Na and Cl- are in higher concentration in the
extracellular fluid
Axon depolarizing
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What drives the action potential?

• opening of Na channels and influx of Na ions

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What happens if sodium channels are blocked?

• lidocaine, novocaine, cocaine
• TTX tetrototoxin
• Sagitoxin-
• red tides

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Concentration Gradient
Electrical Gradient
Na
K
Cl-
after the AP ( intracellular)
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INSIDE AXON
OUTSIDE AXON (EXTRACELLULAR FLUID)
Cl-
K
K
K
Cl-
A-
Na
Cl-
Na
A-
K
Na
A-
Cl-
Na
A-
K
Na
Cl-
Na
K
K
K and negative anions are in higher
concentration in the intracellular or inside the
axon
Neuron at Rest
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Sodium-potassium pump active force that
exchanges 3 Na inside for 2 K outside
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INSIDE AXON
OUTSIDE AXON (EXTRACELLULAR FLUID)
Cl-
K
Na
K
Cl-
A-
Na
Cl-
Na
A-
Na
K
Na
A-
Cl-
Na
Na
A-
K
K
Na
Na
Cl-
Na
K
K
Na
K and negative anions are in higher
concentration in the intracellular or inside the
axon
After the action potential
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conduction or propogation of the action potential

• myelin sheath (80 fat and 20 protein)
• produced by glia

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http//www.blackwellpublishing.com/matthews/channe
l.html
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nodes of ranvier
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conduction or propogation of the action potential

• myelin sheath (80 fat and 20 protein)
• produced by glia
• nodes of ranvier

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nodes of ranvier
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conduction or propogation of the action potential

• myelin sheath (80 fat and 20 protein)
• produced by glia
• nodes of ranvier
• saltatory conduction (200 ft/sec)

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http//www.blackwellpublishing.com/matthews/action
p.html
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Advantages of Saltatory Conduction

• speed, efficiency of neurotransmission

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Advantages of Saltatory Conduction

• speed, efficiency of neurotransmission
• disease Multiple Sclerosis
• progressive, autoimmune disease
• onset 20 years of age
• early symptoms motor symptoms, such as weakness,
  leg dragging, stiffness, a tendency to drop
  things, a feeling of heaviness, clumsiness,

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What about communication between neurons?