How does an SCR start conducting when gate voltage is applied?

[asitiaf]

When we apply voltage to the gate of an SCR, how does it start conducting?
Current passes through gate to cathode. Then how the breakdown of junction j2 occurs?

 

[NascentOxygen]

Hi asitiaf.

Does the SCR transistor pair equivalent answer your question? http://pcbheaven.com/wikipages/TheSCR/