What types of acceleration do the utricle and saccule measure?

The utricle and saccule are components of the vestibular system in the inner ear responsible for detecting linear accelerations and the position of the head relative to gravity. Specifically, they sense changes in the position of the head in a straight line, which is referred to as linear acceleration.

When the head moves linearly, fluid within the utricle and saccule shifts, causing hair cells embedded in a gel-like substance to bend. This bending generates nerve impulses that the brain interprets as movement in a specific direction. The utricle is primarily sensitive to horizontal movements, while the saccule is more responsive to vertical movements.

This function is critical for maintaining balance and spatial orientation in response to linear accelerations, such as when starting or stopping in a vehicle or moving in different directions. Other options such as measuring roll rates or rotational accelerations pertain to different structures in the vestibular system, particularly the semicircular canals, which are responsible for detecting angular or rotational motion. Thus, linear accelerations are accurately captured by the responses from the utricle and saccule, making the focus on displacements and linear accelerations appropriate in this context.