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 monitor sensors and these are still the default used for medical devices. The newer technology is based on optical sensors. ECG (Electrocardiography) sensors measure the bio-potential generated by electrical signals that control the expansion and contraction of heart chambers. PPG (Photoplethysmography) sensors use a light-based technology to sense the rate of blood flow as controlled by the heart's pumping action. The electrical monitors consist of two elements: a monitor/transmitter, which is worn on a chest strap, and a receiver. When a heartbeat is detected a radio signal is transmitted, which the receiver uses to display/determine the current heart rate. This signal