Which statement describes the unilateral action of the scalene muscles?

• A. With ribs fixed, laterally flex the head and neck to the same side and rotate to the opposite side
• B. Elevate the rib cage during inhalation
• C. Flex the head and neck
• D. Extend the neck

Answer: (A)

When one scalene contracts while the ribs are fixed, it bends the neck to the same side (lateral flexion) and turns the head to the opposite side. This occurs because the scalene fibers run from the cervical transverse processes down to the first two ribs, so a one-sided pull drags that side of the neck up and rotates the face away. The other statements describe different actions: elevating the rib cage during inhalation is the inspiratory role of the scalene muscles, not their unilateral neck action; flexing or extending the neck are not the primary unilateral effects of the scalene. So the described unilateral neck movement best captures how the scalene muscles behave when contracting on one side.