The

saccule The saccule is a bed of sensory cells in the inner ear. It translates head movements into neural impulses for the brain to interpret. The saccule detects linear accelerations and head tilts in the vertical plane. When the head moves verticall ...

is the smaller sized

vestibular The Vestibular (from pt, vestíbulo, "entrance hall") is a competitive examination and is the primary and widespread entrance system used by Brazilian universities to select the students admitted. The Vestibular usually takes place from Nove ...

sac (the utricle being the other larger size vestibular sac); it is globular in form, and lies in the recessus sphæricus near the opening of the scala vestibuli of the

cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory o ...

. Its anterior part exhibits an oval thickening, the macula of saccule (or saccular macula), to which are distributed the saccular filaments of the

acoustic nerve The cochlear nerve (also auditory nerve or acoustic nerve) is one of two parts of the vestibulocochlear nerve, a cranial nerve present in amniotes, the other part being the vestibular nerve. The cochlear nerve carries auditory sensory information ...

. The vestibule is a region of the inner ear which contains the

and the utricle, each of which contain a macula to detect

linear acceleration In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by th ...

. Its function is to detect vertical linear acceleration. The macula of saccule lies in a nearly vertical position. It is a 2mm by 3mm patch of hair cells. Each hair cell of the macula contains 40 to 70

stereocilia Stereocilia (or stereovilli or villi) are non-motile apical cell modifications. They are distinct from cilia and microvilli, but are closely related to microvilli. They form single "finger-like" projections that may be branched, with normal cell ...

and one true

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike proje ...

, called a

kinocilium A kinocilium is a special type of cilium on the apex of hair cells located in the sensory epithelium of the vertebrate inner ear. Anatomy in humans Kinocilia are found on the apical surface of hair cells and are involved in both the morphogenesis ...

. A gelatinous cover called the otolithic membrane envelops the tips of the stereocilia and kinocilium. The otolithic membrane is weighted with small densely packed

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

- calcium carbonate granules called statoconica. The macula of the utricle is in a horizontal position and detects horizontal acceleration. The coordinated

sensory perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...

of acceleration both vertically and horizontally along the vestibular nerve, allow for the perception of linear acceleration in any direction. In vertical linear acceleration, the weighted otolithic membrane lags behind the stereocilia and kinocilium. This bends the stereocilia, which is interpreted by the brain as vertical linear acceleration.

References

Vestibular system {{Anatomy-stub