Neurophysiology
1997a(5): What is saltatory conduction and what are the advantages of this
type of conduction?
Many PNS / CNS nerve fibres are coated with a layer of myelin (produced by
Schwann cells of PNS; oligodendrocytes of CNS ) → lipoprotein complex
- Myelin is interrupted at regular intervals where nerve axon is exposed:
Nodes of Ranvier (1μm space) → concentration of ion channels here
Saltatory conduction: Propagation of action potential in a myelinated nerve fibre
where the action potential ‘jumps’ from node to node
- Advantages:
o Very fast conduction of action potential cf unmyelinated fibres (50 x
velocity of unmyelinated conduction)
o ↓axonal size for given conduction velocity
o Less ionic flux (only at NOR) → less energy required to restore
RMP
Unmyelinated nerve conduction
- RMP: -70mV
- Membrane exposed to current: once reaches threshold (~-10mV) →
opening of fast Na channels → membrane depolarisation
o Membrane depolarises to +35mV
o Opening of K+ channels, and closing of fast Na channels →
repolarisation
- Membrane depolarisation (local effect) acts as a current sink and causes
a rise in membrane potential of membrane ahead
o Once reaches threshold → membrane depolarisation and
conduction of the action potential
o Occurs in one direction due to absolute and relative refractory
periods of tissue once it has depolarised
Myelinated nerve conduction
- Once local depolarisation has occurred at Node of Ranvier → myelin
insulates immediately surrounding membrane (↑resistance / ↓capacitance)
→ ↑distance which current sink operates (to next node) → nodal
depolarisation
By Amanda Diaz