Forty years ago this month, five simple notes played on a guitar irrevocably changed the course of popular music. Those simple five notes gave us, in no particular order: Ozzy biting the head off a bat, poodle haircuts, cock-rock posturing, spandex, Spinal Tap, the template for grunge, all those "excess all areas" Motley Crue stories and tons more besides.

Girl, you really got me goin' You got me so I don't know what I'm doin' Yeah, you really got me now You got me so I can't sleep at night.

The first five notes of The Kinks' You Really Got Me single marked the beginning of heavy metal. Strange but true. Here's how it happened: when Ray Davies wrote You Really Got Me, brother Dave was charged with coming up with the intro. The first few times he hacked something out, his girlfriend of the time told him the playing was good but it didn't make her "want to drop her knickers".

To produce something a bit more rasping and distorted, Dave Davies went over to his little amplifier and cut the cone up with a razor blade. The vibration of the fabric produced a hitherto unheard "fuzz" sound and those five notes became one of the most legendary riffs in music. The irony of it all was that, originally, Ray Davies played the intro on a piano, and he thought he had come across a jazz riff.

An urban myth grew up around this intro. To this day, a large proportion of Led Zeppelin fans will tell you that it was Jimmy Page (who, back in 1964, was a noted session guitarist) who played the riff. While Page did play on some Kinks records, he had nothing to do with this song.

"I was so unhappy at not being able to get the right guitar sound on the record," remembers Dave Davies. "It just came out of frustration. I wasn't a particularly articulate kid and hearing the sound I made brought up something within me, a rage. I know it's now seen as being the first ever heavy metal guitar sound but I never really liked that term. I think, in all humility, it should be more properly called the first heavy guitar riff".

Listening to the song now, it seems anything but extraordinary. But then this was 40 years ago and before Davies slashed his amp, the predominant guitar sound was something more like the smooth and clear notes of The Shadows.

The song had a huge impact on Jimi Hendrix, who sought out Dave Davies on a trip to London, cornered him and demanded to know how he had got such a sound out of his guitar. "Hendrix told me it was a landmark song for him," says Davies.

The song raced to No 1 in Britain and even went top 10 in the US. Written as a "love song for street kids", it still retains a potency over and above its historical status.

The origin of the term "heavy metal" still remains uncertain, although many point to the 1962 William S. Burroughs novel, The Soft Machine, which contained a character called "Uranian Willy, the Heavy Metal Kid".

That aside, this new loud and discordant guitar sound made an immediate impression on The Kinks' contemporaries. The Who (who never hid how much they owed The Kinks) began throwing a lot more power chords into their songs and The Beatles (who "borrowed" a lot more than people would have you believe) used a lot of You Really Got Me when they came up with Helter Skelter, albeit more in tone than content.

The received wisdom is that the Jeff Beck Group's Truth album of 1968 is the first real heavy rock/metal album but, in terms of sheer impact, that honour surely must go to the 1969 Led Zeppelin. Since then the music had been distorted and fragmented out of all recognition. One consistent thing though: as a genre it remains - and stubbornly so - largely a white, male, teenage phenomenon.

To mark the anniversary, Sanctuary Records have re-released the You Really Got Me single. Kerrang!