[Propagation of stimuli].
Cardiac muscle is considered as a biological cable, similar to fibres of skeletal muscle or nerve. "Local currents" within the core of the cable and through the extracellular space are responsible for the propagation of membrane excitation. Conduction velocity depends on (i) fibre diameter, (ii) specific resistance of the core and interstitial fluid, (iii) strength of possible inward current through the surface membrane. Conduction delay and possible block is found at sites of transition between terminal Purkinje fibres and ventricular muscle. Monophasic action potentials of somewhat different shapes are recorded from various parts of the heart. A slow upstroke is characteristic for sites of low conduction velocity (SA-node, AV-node). A progressive decrease of resting potential in the phase of diastole is typical for regions showing a tendency to automatic impulse generation (SA-node, AV-node, Purkinje fibres). Cardiac muscle is a functional syncytium. This statement is based on (i) measurements of electrical resistance between cells and (ii) diffusion experiments using tracer substances. Progressive de-coupling is observed under various pathological conditions, resulting in slow conduction or block.
D000200:Action Potentials; D002463:Cell Membrane Permeability; D004594:Electrophysiology; D006321:Heart / Q000502:physiology*; D008564:Membrane Potentials
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