The Unified Mechanical Model of Neurotransmission: A Mechanical-First Hypothesis of Continuous Axonal Signal Propagation and Pressure-Differential Ion-Channel Gating

Abstract

Neural transmission is conventionally understood primarily as an electrical process in which voltage-dependent ion channels generate and regenerate action potentials along neuronal membranes. The Unified Mechanical Model of Neurotransmission (UMMN) proposes an alternative physical interpretation of axonal signal propagation. The central hypothesis of UMMN is that the primary signal travelling along the axon is a continuously propagating mechanical pressure wave, termed the Action Pressure Wave (APW). The electrical events conventionally recorded as action potentials are proposed to represent local electrical manifestations of this mechanically propagating signal rather than the primary long-range carrier of neural information. The model does not dispute the existence or importance of ion channels, ionic currents, membrane potentials, or action potentials. Instead, it proposes a different causal interpretation of their activation during propagation. Specifically, UMMN hypothesizes that the relevant ion-channel gates are mechanically influenced by a transient pressure differential across the gating structure. During the phase in which intra-axonal pressure falls below its resting value, extracellular pressure is proposed to become transiently greater than intracellular pressure, producing a mechanical force capable of displacing the channel gate and permitting ionic influx. The proposed causal sequence is therefore: Pressure differential → mechanical gate displacement → ion-channel opening → ionic current → change in internal charge relative to its resting value → local electrical potential change (action potential) A second defining feature of UMMN concerns myelinated axons. The model does not propose that the primary neural signal travels by electrically jumping from one Node of Ranvier to another. Instead, the APW is hypothesized to propagate continuously through the entire axonal pathway, including the internodal regions. The Nodes of Ranvier are proposed to be specialized sites where the continuously propagating mechanical wave interacts with the membrane and ion-channel structures, producing localized electrical responses. The model further proposes that electrical initiation occurs at the axon hillock, where a mechanically active cytoskeletal structure may generate the initial APW. A candidate mechanism is described as a hypothetical "nano-piston," although this component remains speculative and requires direct experimental investigation. The principal experimental prediction of UMMN is that the pressure change responsible for channel activation should precede the corresponding ionic current and the change in internal charge relative to its resting value, at the axon hillock, at each node of Ranvier, and at the terminal bouton. This temporal sequence constitutes the central experimental test of the model. UMMN is therefore presented as a falsifiable hypothesis rather than an established mechanism. Its validity depends on direct experimental demonstration of mechanical precedence, quantitative sufficiency, causal influence on ion-channel gating, and continuous mechanical propagation along the axon. Keywords: Action Pressure Wave; mechanical neurotransmission; axonal conduction; pressure-differential gating; ion channels; Nodes of Ranvier; myelin; mechanotransduction; action potential