The utricle and saccule detect which types of motion?

• A. Linear acceleration and head tilt relative to gravity
• B. Angular acceleration
• C. Rotational velocity
• D. Sound frequency

Answer: (A)

The utricle and saccule are vestibular otolith organs that sense linear motion and head position relative to gravity. Inside each macula, hair cells with stereocilia sit in a gelatinous layer topped by otoliths (calcium carbonate crystals). When the head moves in a straight line or tilts, the inertia of the otoliths causes a shearing force on the gelatinous layer, bending the hair cell stereocilia and producing electrical signals. This positive or negative deflection encodes linear acceleration and the orientation of the head with respect to gravity.

The utricle is oriented to detect horizontal linear acceleration, while the saccule is oriented to vertical linear acceleration, but both contribute to sensing tilt and linear motion. Angular acceleration and rotational movement are detected by the semicircular canals, not the otolith organs, and sound frequency is processed by the cochlea.