Neuroscience II The Nerve Impulse

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Neuroscience IIThe Nerve Impulse
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The Nerve Impulse

• Mechanisms of Transmission
• Depolarization
• Repolarization
• The Action Potential

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The Nerve Impulse

• AP travels down the axonNa channels open
• AP reaches the synaptic bulbCa channels open
• Neurotransmitters are exocytosed into the synapse
• Neurotransmitters bind to the post-synaptic
  membrane on specific receptors
• Post-synaptic binding causes opening of Na
  channels and current flow process continues

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Measuring impulse

• ??

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• Sodium-Potassium pump uses ATP to pull K in and
  push Na out

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Action Potential
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The Action Potential

• At rest
• Out High Na, low K
• In Low Na, High K
• Depolarization Na channels open, Na rushes in

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Membrane Permeability

• Donnan Equilibrium
• 1. K I C1- II
• _____________
• 3. K II C1 I
• Nernst Equation
• 1. VM or Ex .058 log PK KoPNaNao
  PK KIPNaNai

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The Action Potential

• When mV is , K channels open
• Repolarization K rushes out
• Hyperpolarization Too much K has left the cell
  and it voltage is lower than at the baseline state

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Membrane Conductance

• Understand gNa gk
• Note models of channel design in text
• Saltatory conduction
• Transmission velocity down axons
• Larger diameter axons have faster velocities

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Refractory Periods

• Absolute refractory period
• No AP is possible
• Relative refractory period
• An AP is possible, with lower amplitude (normally
  it is an all-or-none phenomenon)

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Two Types of neuron responses
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Voltage clamping

• Membrane was clamped at 60 mV
• INa gNa (Vm ENa)
• I current
• g conductance
• V voltage or membrane potential
• E Equilibrium potential

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Speed of conduction

• Larger diameter greater conductance
• Myelination greater conductance
• Greater speed greater conductance less
  resistance

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Common Neurotransmitters

• Catecholamines
• Norepinphrine, Epinephrine, Dopamine
• Indolamines
• Serotonin, Melatonin
• Others
• Acetylcholine, NO, GABA, Opioids, etc.

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Neurotransmitters

• Peripheral
• Central
• Final Common Pathway
• Neuron Placement Circuits
• Converging Circuit
• Diverging Circuit
• Reverberating Circuit
• Parallel Circuit
• Simple Circuit

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• THE END