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The brain integrates information through networks of neurons that communicate through action potentials (AP). The Hodgkin-Huxley model describes the ionic dynamics of a PA: Na (fast entry, depolarization) and K (slow exit, repolarization) currents through voltage-gated channels, governed by gate variables m, h, n with their own kinetics.

The Goldman equation describes the resting potential (~70 mV) as a result of the balance of ionic permeabilities. At rest, P_K >> P_Na, so V_m approaches the Nernst potential of K (~90 mV). Rall's cable model predicts how the potential is attenuated in the dendritic tree: and _m determine how far and how long the influence of a synapse lasts.

The conduction velocity v_cond d in myelinated fibers (saltatorial, from node to node) and d in unmyelinated fibers. This explains why fast motor fibers (A, d = 1320 m) conduct at 70120 m/s, while slow pain fibers (C, d = 0.31.5 m) conduct at 0.52 m/s.

The human brain consumes ~20 W (20% of total metabolic expenditure) despite representing only 2% of body mass. Each action potential requires ~10 Na ions that must be returned by the Na/K-ATPase (3 ATP per pump cycle). Brain oscillations (EEG: , , , , ) emerge from the collective resonance of networks of equivalent LC circuits between membrane capacitances and synaptic inductances.

Clinically, nerve conduction velocity (electromyography/electroneurography) distinguishes demyelinating neuropathies (reduced v_cond, increased _m) from axonal neuropathies (reduced amplitude, normal v_cond). Brain rhythms (EEG) are indicators of state of consciousness, epilepsy (pathological / hypersynchrony) and anesthetic depth ( dominance).

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ID:(0, 33)