Cell signaling of adjacent cells. In cardiac muscle, gap junctions between adjacent cells allows for action potential propagation from the cardiac pacemaker region of the heart to spread and coordinately cause contraction of the heart. The notch signaling mechanism is an example of juxtacrine signaling (also known as contact-dependent signaling) in which two adjacent cells must make physical contact in order to communicate. This requirement for direct contact allows for very precise control of cell differentiation during embryonic development. In the worm "Caenorhabditis elegans", two cells of the developing gonad each have an equal chance of terminally differentiating or becoming a uterine
Heart rate turbulence Heart rate turbulence Heart rate turbulence (HRT) is the return to equilibrium of heart rate after a premature ventricular contraction (PVC). It consists of a brief speed-up in heart rate, followed by a slow decrease back to the baseline rate. An important feature of HRT is that PVCs occur naturally in most adults, so measuring the characteristics of a given person's HRT offers a noninvasive way to evaluate his or her cardiac function without applying artificial external stimuli. The measured values of HRT parameters have been shown to be a statistically significant predictor of the probability of dying from cardiac