An action potential is a "spike" of positive and negative ionic discharge that travels along the membrane of a cell. Action potentials are an essential feature of animal life, rapidly carrying information within and between tissues. They also occur in some plants. Action potentials can be created by many types of cells, but are used most extensively by the nervous system for communication between neurons and for transmitting information from neurons to other body tissues such as muscles and glands.

Action potentials are not the same in all cell types and can even vary in their properties at different locations in the same cell. For example, cardiac action potentials are significantly different from the action potentials in most neurons. This article is primarily concerned with the "typical" action potential of axons.

Threshold is a progressive metal band, formed in Surrey, UK in the late 1980s.

There are two bands with the name Threshold: a progressive metal band and an R&B band. 1. A progressive metal band from the South of England, consisting of Mac (vocals), Karl Groom (guitar), Richard West (keyboards), Steve Anderson (bass) and Johanne James (drums). The band’s early years saw four highly acclaimed albums released through the independent label GEP. After some line-up changes and many tours in Europe alongside bands such as Dream Theater, Threshold signed to Inside Out Music in 2