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Figure 1 | Cerebellum & Ataxias

Figure 1

From: Peripheral nerve axonal excitability studies: expanding the neurophysiologist’s armamentarium

Figure 1

Diagram of a myelinated axon illustrating ion channels, pumps and exchangers responsible for determining axonal excitability. Transient Na+ channels (Nat) are clustered at high density at the node of Ranvier, with persistent Na+ channels (Nap) and slow K+ channels (Ks) contributing to excitability and resting membrane potential. Fast K+ channels (Kf) are located at highest density at the juxtaparanode, acting to limit re-excitation of the node following an action potential. Internodal conductances include voltage-independent ‘leak’ conductances (Lk) and hyperpolarization-activated cation conductance (IH). The Na+–K+ pump (Na+/K+-ATPase) utilises energy to maintain the electrochemical gradient necessary for impulse conduction by removing 3 Na+ ions for every 2 K+ ions pumped into the axon. The Na+–Ca2+ exchanger exports Ca2+ ions and imports Na+, driven by the electrochemical Na+ gradient. Paranodal myelin terminal loops are depicted with anchoring proteins to form paranodal junctions at the paranodal region.

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