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Our facial muscles and their functions

The human face is the most sophisticated and context-rich communication tool that ever existed. It was perfected for its purpose by millions of years of evolution. Whenever we feel joy or sadness, become scared or surprised – our facial muscles contract and relax with precision and in excellent harmony. They deliver our message to the world. Just one smile can tell us much more than a thousand words.

“I want my smile back!” This is the number one wish of all Bell’s palsy sufferers. To produce a genuine smile, we need a highly coordinated work of many facial muscles. This can become quite a challenge if the recovery takes longer than a couple of months.

Note: This article is also available in a video format in our Bell’s Palsy Video Courses.

The muscles of facial expressions

Let’s take a closer look at our facial muscles, their names and functions. Please study the facial muscles carefully. This will be important later when we discuss the causes and the recovery of Bell’s palsy, as well as synkinesis.

Before we go on, we need to understand what are muscle synergists and antagonists. Muscles that “help” each other to produce a certain movement are called synergists. Muscles that produce movements in opposite directions are called antagonists.

Facial muscles
Facial muscles

The facial muscles and their functions:

Frontalis muscle – lifts the eyebrows, makes horizontal forehead wrinkles when we are surprised.

Orbicularis oculi – the circular muscle of the eye (consists of two muscles). Closes the eyelids, squints the eye. These two muscles are antagonists. Lift and hold your eyebrow with your finger and then try to squint your eyes. Difficult, isn’t it?

Procerus – is a frown muscle. Pulls medial sides of eyebrows down and together.

Corrugator superclii – pulls eyebrows together.

Zygomatic muscles (major and minor) – move the mouth corners up and outward when we smile.

Risorius – the “smile” muscle. Pulls mouth corners laterally (outward) and forms dimples in the cheeks. This muscle is not always active in all people.

Orbicularis oris – the circular muscle of the mouth. Puckers the lips and brings mouth corners towards the middle line.

Depressor anguli oris – pulls mouth corners downward.

Levator labii superioris and depressor labii inferioris – pull the upper and lower lips up and down respectively when we grin.

Mentalis – the chin muscle. Pulls up the chin as we express disappointment, doubt and some other negative emotions.

Platysma – it is a surface muscle of the neck. The platysma is engaged in the expressions of fear, disgust and some other negative emotions.

How does the “crooked” smile happen?

The “crooked” or asymmetrical smile after Bell’s palsy happens when depressor anguli oris muscle on the affected side is unnecessarily activated together with zygomatic muscles, which are its antagonists. These muscles become engaged when you are trying to make a smile. In this “fight” the depressor anguli oris muscle often wins over the latter, simply because it is larger and stronger. Since this muscle is responsible for moving the mouth corner downwards, the result is that the affected side “looks down” instead of “up”. Quite often, several small dimples may appear on that side of the chin, leading to a further disfigurement of facial expressions.

Bell's palsy - synkinetic smile
Broad smile
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Alex Pashov

Co-founder of Crystal Touch clinic and Bell's palsy expert.

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