Action of lateral vs. medial Pterygoid muscle "mnemonic"

Look at how your jaw ends up when saying first syllable of 'Lateral' or 'Medial' :

1. -"La": your jaw is now open, so Lateral opens mouth.
2. -"Me": your jaw is still closed, so medial closes the mandible.

medial pterygoid muscle

Origin : deep head: medial side of lateral pterygoid plate behind the upper teeth
superficial head: pyramidal process of palatine bone and maxillary tuberosity
Insertion : medial angle of the mandible
Actions : elevates mandible, closes jaw, helps lateral pterygoids in moving the jaw from side to side

Lateral pterygoid muscle

Origin :  Great wing of sphenoid and pterygoid plate
Insertion : Condyle of mandible
Actions : depresses mandible, Protrude mandible, side to side movement of mandible