PY 105 Chapter Notes - Chapter 2: Saltatory Conduction, Action Potential, Central Nervous System
Action Potential
Depolarization
• Voltage gated sodium channels propagate action potentials
• These ion channels open to allow sodium ions to flow down their gradient into the cell
and depolarize that section of the membrane
• These channels are opened by depolarization of the membrane from the resting potential
of -70mV to a threshold potential of -50mV
• When threshold is reached, the channels are opened fully
o Open channels: sodium flows into the cell, down concentrations gradient,
depolarizing that section to +35mV
Repolarization
• Reestablishes original resting membrane potential
1. Voltage gated sodium channels inactivate very quickly after they open, shutting off flow of
sodium into the cell. Channels remain inactivated until membrane potential nears resting
values
2. Voltage gated potassium channels open more slowly than voltage gated sodium channels
and stay open longer
3. Potassium leak channels and Na+/K+ ATPase bring membrane back to resting potential
Saltatory Conduction
• Axons are wrapped in an insulating sheath called myelin created by Schwann cells
• No ions can enter or exit a neuron where the axonal membrane is covered with myelin
• There are periodic gaps called nodes of Ranvier
o Voltage gated sodium and potassium channels are concentrated in the nodes
• Myelin speeds the movement of action potentials by forcing it to jump from node to node
• The rapid jumping conduction is called saltatory conduction
Glial Cells
• Specialized, non-neuronal cells that provide structural and metabolic support to neurons
1. Schwann cells
a. Peripheral Nervous system
b. Form myelin; increases speed of conduction of action potentials
2. Oligodendrocytes
a. Central nervous system
b. Form myelin; increase speed of conduction of action potentials
3. Astrocytes
a. Central nervous system
b. Guide neuronal development
c. Regulate synaptic communication via regulation of neurotransmitter levels
4. Microglia
a. Central nervous system
b. Remove dead cells and debris
5. Ependymal cells
a. Central nervous system
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