Where does junction collide?

The boundary formed inside a semiconductor crystal where a region doped to carry positive charge carriers (p-type) meets a region doped to carry negative carriers (n-type): at this interface a built-in electric field appears that lets current pass easily one way and blocks it the other, which is what makes diodes, transistors, and solar cells work. Shockley's 1949 The Theory of p-n Junctions in Semiconductors and p-n Junction Transistors set out the physics of this rectifying boundary and the transistor built from it. The referent is a doped interface in a solid crystal, defined by how it steers electric current, and it is not a link between living cells, a nerve-to-muscle contact, or a place where roads meet.[1]

Unit

A rectifying interface between p-type and n-type material, one per device

Recovery means

Not applicable

Measured by

Characterised by its current-voltage curve, junction capacitance, and reverse breakdown voltage

Any of the specialised structures that hold neighbouring cells together or seal the space between them, forming the junctional complex that Farquhar and Palade's 1963 Junctional Complexes in Various Epithelia mapped in epithelial tissue: a tight junction that seals the gap and controls what leaks between cells, and an adherens junction and desmosome that anchor cell to cell for mechanical strength. The referent is a family of adhesive and barrier structures that build a tissue by joining its cells, and it controls adhesion and permeability rather than passing electric current. It differs from the channel-forming gap junction, and it is not a doped crystal interface, a nerve-to-muscle synapse, or a road crossing.[2]

Unit

A cell-to-cell adhesive or sealing structure at a tissue boundary

Recovery means

Not applicable

Measured by

Visualised by electron microscopy and identified by its junction proteins, such as claudins and cadherins

The synapse where a motor nerve fibre meets a skeletal muscle fibre and hands over the command to contract: the nerve terminal releases the chemical acetylcholine, which crosses a narrow cleft and triggers an electrical change in the muscle membrane called the end-plate potential. Fatt and Katz's 1951 An Analysis of the End-Plate Potential Recorded with an Intra-Cellular Electrode measured that signal and laid the groundwork for understanding chemical transmission at this contact. The referent is a nerve-to-muscle chemical synapse that turns a nerve impulse into a muscle twitch, and it is not a semiconductor interface, an adhesive cell structure, or a place where roads meet.[3]

Unit

One nerve-to-muscle synaptic contact that transmits the signal to contract

Recovery means

The end-plate repolarises between impulses as acetylcholine is broken down and the membrane resets

Measured by

Recorded by intracellular electrodes as end-plate potentials, and mapped by staining acetylcholine receptors