David Williams, of Hataitai, asks :-

I have read the quote “It takes 17 muscles to smile and 43 to frown.� Is this true?

Philip Sheard, a physiologist at the University of Otago, responded.

In short, no. The total number of muscles in the face varies a little from person to person, but the number is likely to be between 40 and 43. The statement that 43 muscles are involved in a frown therefore suggests that all facial muscles are involved in a frown, and since the muscles that turn the corners of the mouth upwards in a smile are unlikely also to be activated when turning the corners of the mouth down for a frown, that aspect of the statement is unlikely to be true.

Smiles and frowns are not stereotyped all-or-none events, they can each be executed at various levels of enthusiasm. At its simplest level we might think of an insincere smile as a modest upturning of the corners of the mouth with a little pouting of the lips, and probably about 10 muscles are used to produce this action (many muscles are present in pairs, often symmetrically on both sides of the face). A similarly minimal frown, a downturn of the corners of the mouth, probably uses only about 6 muscles (3 pairs). If we were to progressively increase the intensity of the expression to incorporate movements in the forehead, the cheeks, the chin, and around the eyes, then more of the complex muscles of the face would be used. In each case, the number of muscles used would relate not only to the nature of the expression (smile or frown) but also to the enthusiasm of the individual’s behaviour: a broad smile on a happy face will likely employ more muscles than a superficial frown, for instance.

Some facial muscles will typically be used to generate a smile, some a frown, and some may be used in both instances. For example, the Zygomaticus (major and minor) muscles tend to pull the corners of the mouth up for a smile, whilst the Depressor anguli oris pulls the corners of the mouth down when frowning. The Corrugator supercilii pulls the eyebrows down and towards the midline causing the furrowing of the brow that is a distinctive feature of a deep frown, whilst Risorius pulls the corner of the mouth outwards to broaden the smile. By contrast, Orbicularis oculi (involved in closing the eyes) may be activated in both smiles and frowns.

So, the statement that 17 muscles are required to smile but 43 to frown suggests a consistent, stereotyped activation pattern that oversimplifies these two complex behaviours and which almost certainly renders the statement incorrect.

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