sense of linear motion

The spatial orientation modality that senses translation.

dizziness

A commonly used lay term that nonspecifically indicates any form of perceived spatial disorientation, with or without instability.

transduce

To convert from one form of energy to another (e.g., from light to neural electrical energy, or from mechanical movement to neural electrical energy).

amplitude

The size (increase or decrease) of a head movement (e.g., angular velocity, linear acceleration, tilt).

balance

The neural processes of postural control by which weight is evenly distributed, enabling us to remain upright and stable.

tilt

Attaining a sloping position like that of the leaning tower of Pisa.

vertigo

A sensation of rotation or spinning. The term is sometimes used erroneously to mean any form of dizziness.

mechanoreceptor

A sensory receptor that responds to mechanical stimulation (pressure, vibration, or movement).

spatial disorientation

Any impairment of spatial orientation. More specifically, any impairment of our sense of linear motion, angular motion, or tilt.

utricle

One of the two otolith organs. A saclike structure that contains the utricular macula. Also called utriculus.

autonomic nervous system

The part of the nervous system that innervates glands, heart, digestive system, and so on, and that is responsible for regulating many involuntary actions.

hair cell

Any cell that has stereocilia for transducing mechanical movement in the inner ear into neural activity sent to the brain; some hair cells also receive inputs from the brain.

receptor potential

A change in voltage across the membrane of a sensory receptor cell (in the vestibular system, a hair cell) in response to stimulation.

sinusoidal

Referring to any oscillation, such as a sound wave or rotational motion, whose waveform is that of a sine curve. The period of a sinusoidal oscillation is the time that it takes for one full back-and-forth cycle of the motion to occur. The frequency of a sinusoidal oscillation is defined as the numeral 1 divided by the period.

angular motion

Rotational motion like the rotation of a spinning top or swinging saloon doors that rotate back and forth.

spatial orientation

A sense consisting of three interacting sensory modalities: the senses of linear motion, angular motion, and tilt.

direction

The line along which one faces or moves, with reference to the point or region toward which one is facing or moving.

vestibular organs

The set of five organs—three semicircular canals and two otolith organs—located in each inner ear that sense head motion and head orientation with respect to gravity. These organs are also sometimes called the vestibular system or the vestibular labyrinth, but the name vestibular system is often used more generally to refer to the vestibular organs and their neural pathways.

angular acceleration

The rate of change of angular velocity. Mathematically, the integral of angular acceleration is angular velocity, and the integral of angular velocity is angular displacement. Angular acceleration, angular velocity, and angular displacement all mathematically represent angular motion.

otoconia

Tiny calcium carbonate stones in the ear that provide inertial mass for the otolith organs, enabling them to sense gravity and linear acceleration.

sense of tilt

The spatial orientation modality that senses head inclination with respect to gravity.

macula

Any of the specialized detectors of linear acceleration and gravity found in each otolith organ.

sense of angular motion

The spatial orientation modality that senses rotation.

ampulla

An expansion of each semicircular canal duct that includes that canal’s cupula, crista, and hair cells, where transduction occurs.

balance system

The sensory systems, neural processes, and muscles that contribute to postural control. Specific components include the vestibular labyrinth, proprioceptors, vestibulo-spinal pathways, and postural control muscles. Because of its crucial contributions to balance, some even informally refer to the vestibular system as the balance system and the vestibular organs as the balance organs. But the balance system is much more than just the vestibular system, and the vestibular system contributes to much more than just balance.

Fourier analysis

A mathematical procedure by which any signal—in this case motion trajectories as a function of time—can be separated into component sine waves at different frequencies. Combining these sine waves will reproduce the original motion trajectory.

vestibulo-ocular reflex (VOR)

A short-latency reflex that helps stabilize vision by counterrotating the eyes when the vestibular system senses head movement.

otolith organ

Either of two mechanical structures (utricle and saccule) in the vestibular system that sense both linear acceleration and gravity.

mathematical integration

Computing an integral—one of the two main operations in calculus (the other, the inverse operation, is differentiation). Velocity is the integral of acceleration. Change of position is the integral of velocity.

semicircular canal

Any of three toroidal tubes in the vestibular system that sense angular motion.

gravity

A force that attracts a body toward the center of the Earth.

crista

Any of the specialized detectors of angular motion located in each semicircular canal in a swelling called the ampulla.

vection

An illusory sense of self-motion caused by moving visual cues when you are not, in fact, actually moving.

saccule

One of the two otolith organs. A saclike structure that contains the saccular macula. Also called sacculus.

linear acceleration

The rate of change of linear velocity. Mathematically, the integral of linear acceleration is linear velocity, and the integral of linear velocity is linear displacement, which is also referred to as “translation.” Linear acceleration, linear velocity, and linear displacement all mathematically represent linear motion.

acceleration

A change in velocity. Mathematically, acceleration is the derivative of velocity. In words, linear acceleration indicates a change in linear velocity; angular acceleration indicates a change in angular velocity.

sensory integration

The process of combining different sensory signals. Typically, combining several signals yields more accurate and/or more precise information than can be obtained from individual sensory signals. This is not the mathematical process of integration learned in calculus (e.g., the integral of acceleration is velocity).

cilium

Any of the hairlike structures that move as part of vestibular transduction. The vestibular system includes two types of cilia: kinocilia and stereocilia.

velocity

The speed and direction in which something moves. Mathematically, velocity is the integral of acceleration. In words, linear velocity is the ratio of the distance moved divided by the time it takes to traverse that distance; angular velocity is the ratio of the angle rotated divided by the time it takes to traverse that angle.

oscillatory

Referring to back-and-forth movement that has a constant rhythm.

imbalance

Lack of balance; unsteadiness; nearly falling over.

linear motion

Translational motion like the predominant movement of a train car or bobblehead doll.