National Physical Therapy Examination (NPTE) Practice Exam

Which muscle primarily causes mandible depression and contributes to jaw deviation?

1. Medial pterygoid

2. Temporalis

3. Lateral pterygoid

4. Masseter

The correct answer is: Lateral pterygoid

The lateral pterygoid muscle is primarily responsible for mandible depression and plays a significant role in the deviation of the jaw. This muscle has two heads, and when it contracts bilaterally, it allows for the depression of the mandible, which is the downward movement of the jaw essential for actions like opening the mouth. Additionally, the lateral pterygoid is crucial for various movements of the jaw during chewing, including the lateral and protrusive movements, which contribute to the side-to-side motion and slight forward movement of the mandible. When it contracts unilaterally, it causes the jaw to deviate to the opposite side, aiding in the grinding movement necessary for mastication. The other muscles mentioned have supportive roles rather than primary functions in mandible depression. The medial pterygoid, for instance, works more on elevating the mandible alongside the masseter, while the temporalis mainly contributes to elevation and retraction of the mandible, not depression. Therefore, the lateral pterygoid's specific function in depression and deviation makes it the correct answer.