Human Head, Neck, Eye muscles

Epicranius (frontalis), Levator labii superioris, Orbicularis oculi, Orbicularis oris, Buccinator, Masseter,

Zygomaticus, Temporalis

1

2

3

4

5 6

67

Epicranius

Levator labii superioris

Orbicularis oculi

Buccinator

MasseterOrbicularis oris

Zygomaticus

Temporalis

Massetor

Buccinator

Epicranius

Orbicularis oculi

Orbicularis oris

Levator labii superioris

Massetor

Zygomaticus

Epicranius

Orbicularis oculi

Orbicularis oris

Massetor

What muscles were damaged?

Epicranius muscle action

• http://www.funnieststuff.net/viewmovie.php?id=3201

Smiling

• The French neurologist, Duchenne du Boulogne, writing in the nineteenth century, made a fundamental discovery about the nature of smiling, a discovery that was forgotten for a hundred years. Duchenne electrically stimulated different positions on the face of a patient who had no pain sensation, and photographed the resulting expressions. By this means he learned how the different facial muscles produced different expressions. He showed that the zygomatic major muscle, which runs from the cheek bone down to the lip corners, pulls those lip corners upwards into a smiling shape (Fig. 1). Importantly, Duchenne noted that the man in this picture did not really look happy. He told him a joke, and noted that, when the man smiled spontaneously, it involved not just the zygomatic major, but part of a second muscle, the orbicularis oculi, which encircles the eye (Fig. 2). Duchenne noted that this is a muscle that most people cannot contract voluntarily, and so it ‘unmasks the false friend’.

Smiling

• In 1982, Paul Ekman resurrected Duchenne's distinction to explain why people often smile when they are not happy. As Duchenne had noted, Ekman found that people who smile when they are not feeling enjoyment do not show activity of the muscle around the eyes, just the lip muscle. Many studies now support Duchenne's distinction between these two types of smiling — what scientists now call, in honour of Duchenne, Duchenne smiles, or D-smiles for short (zygomatic major outer part, and orbicularis oculi) and non D-smiles ( zygomatic major only). For example, 5-month-old infants show D-smiles when approached by their mother, non D-smile when approached by a stranger. In adults the D-smile is accompanied by the pattern of brain activity found with enjoyment, but that brain activity pattern is not found when the non D-smile is shown. Happily married couples show D-smiles when they meet at the end of the day, while unhappily married couples show non D-smiles.

Smiling

Non-Duchenne smile Duchenne smile

Smiling

• It is not always easy to distinguish these two types of smiles. If the lips are pulled only slightly or moderately by the zygomatic major muscle, it is easy to see whether the eye muscle is involved, for it will produce crow's feet wrinkles and bagging of the skin under the eyes. Those signs are absent in a slight to moderate non D-smile. However, when the smile is very broad, the lip pulling itself will produce those changes in the face and it is necessary to look elsewhere. Only in the D-Smile will the eyebrows move down ever so slightly.

• Instead of signalling genuine enjoyment, non D-smiles serve many different social functions. They may indicate agreement, they show a person is willing to go along with something, even something unpleasant (grin and bear it), and they may also be used to send a false message of enjoyment when none is felt. Research has shown that most people do not notice the difference between D-smiles and non D-smiles, and it is hard not to reciprocate a smile, even a non-D smile.

Superior, Inferior, Medial, Lateral rectus, Superior, Inferior oblique

Superior Rectus

Superior Rectus

Inferior Rectus

Inferior Rectus

Medial RectusLateral

Rectus

Superior oblique

Superior oblique

Inferior oblique

Inferior oblique

Direction of action of the Eye Muscles

MedialLateral

Superior rectus

Lateral rectusMedial rectus

Inferior Oblique

Superior oblique

Superior oblique Superior rectus

Lateral rectus

Inferior rectus

Superior rectus

Lateral rectusMedial rectus

Inferior Oblique Inferior rectus

This is a RIGHT eye.

Superior rectus

Lateral rectusMedial rectus

Superior Oblique

This is a RIGHT eye.

Superior rectus

Lateral rectus

Inferior Oblique

This is a RIGHT eye.

Lateral rectus

Inferior oblique

Medial rectus

This is a left eye.

Inferior oblique

Lateral rectus

This is a left eye.

Sternocleidomastoid

Sternohyoid

Thyrohyoid

Sternothyroid

Sternocleidomastoid

Digastric

Mylohyoid

Sternocleidomastoid

Sternohyoid

Sternothyroid

Thyrohyoid