OPTION 3

Muscles Producing Movements

 

•            ↓ Depression is brought about mainly by the lateral pterygoid. The digastric, geniohyoid and mylohyoid muscles help when the mouth is opened wide or against resistance.

•            The origin of only lateral pterygoid is anterior, slightly lower and medial to its insertion. During contraction, it rotates the head of mandible and opens the mouth. During wide opening, it pulls the articular disc forwards. So, movement occurs in both the compartments. It is also done passively by gravity.

•            ↑ Elevation is brought about by the masseter, the anterior vertical, middle oblique fibres of temporalis, and the medial pterygoid muscles of both sides. These are antigravity muscles.

•            ← Protrusion is done by the lateral and medial pterygoids and superficial oblique fibres of masseter.

 

 

•            → Retraction is produced by the posterior horizontal fibres of the temporalis and deep vertical fibres of masseter.

•            Lateral or side-to-side movements, e.g. chewing from left side produced by right lateral pterygoid, right medial pterygoid which push the chin to left side.

•            Then left temporalis (anterior fibres), left masseter (deep fibres) (↔) chew the food. Chewing from right side involves left lateral pterygoid, left medial pterygoid, right temporalis and right masseter. Since, so many muscles are involved, chewing becomes tiring.