Sense Of Balance
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The sense of balance or equilibrioception is the
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 syste ...
of
balance Balance may refer to: Common meanings * Balance (ability) in biomechanics * Balance (accounting) * Balance or weighing scale * Balance, as in equality (mathematics) or equilibrium Arts and entertainment Film * Balance (1983 film), ''Balance'' ( ...
and
spatial orientation In geometry, the orientation, attitude, bearing, direction, or angular position of an object – such as a line, plane or rigid body – is part of the description of how it is placed in the space it occupies. More specifically, it refers to t ...
. It helps prevent
human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...
s and nonhuman
animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...
s from falling over when standing or moving. Equilibrioception is the result of a number of
sensory systems The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons (including the sensory receptor cells), neural pathways, and parts of the brain involved i ...
working together; the eyes (
visual system The visual system is the physiological basis of visual perception (the ability to perception, detect and process light). The system detects, phototransduction, transduces and interprets information concerning light within the visible range to ...
), the inner ears (
vestibular system The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating motor coordination, movement with balance. Together with the cochlea, a part of the auditory sys ...
), and the body's sense of where it is in space (
proprioception Proprioception ( ) is the sense of self-movement, force, and body position. Proprioception is mediated by proprioceptors, a type of sensory receptor, located within muscles, tendons, and joints. Most animals possess multiple subtypes of propri ...
) ideally need to be intact. The vestibular system, the region of the inner ear where three semicircular canals converge, works with the visual system to keep objects in focus when the head is moving. This is called the vestibulo-ocular reflex (VOR). The balance system works with the visual and
skeletal system A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fra ...
s (the muscles and joints and their sensors) to maintain orientation or balance. Visual signals sent to the
brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...
about the body's position in relation to its surroundings are processed by the brain and compared to information from the vestibular and skeletal systems.


Vestibular system

In the vestibular system, equilibrioception is determined by the level of a
fluid In physics, a fluid is a liquid, gas, or other material that may continuously motion, move and Deformation (physics), deform (''flow'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are M ...
called
endolymph Endolymph is the fluid contained in the membranous labyrinth of the inner ear. The major cation in endolymph is potassium, with the values of sodium and potassium concentration in the endolymph being 0.91  mM and 154  mM, respectively. ...
in the
labyrinth In Greek mythology, the Labyrinth () is an elaborate, confusing structure designed and built by the legendary artificer Daedalus for King Minos of Crete at Knossos. Its function was to hold the Minotaur, the monster eventually killed by the h ...
, a complex set of tubing in the inner ear.


Dysfunction

When the sense of balance is interrupted it causes
dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to Balance disorder, disequilibrium or a non-specific feeling, such as giddiness or foolishness. Dizziness is a ...
,
disorientation Orientation is a function of the mind involving awareness of three dimensions: time, place and person. Problems with orientation lead to ''dis''orientation, and can be due to various conditions. It ranges from an inability to coherently understand ...
and
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. It can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the throat. Over 30 d ...
. Balance can be upset by
Ménière's disease Ménière's disease (MD) is a disease of the inner ear that is characterized by potentially severe and incapacitating episodes of vertigo, tinnitus, hearing loss, and a feeling of fullness in the ear. Typically, only one ear is affected in ...
, superior canal dehiscence syndrome, an inner ear infection, by a bad
common cold The common cold, or the cold, is a virus, viral infectious disease of the upper respiratory tract that primarily affects the Respiratory epithelium, respiratory mucosa of the human nose, nose, throat, Paranasal sinuses, sinuses, and larynx. ...
affecting the head or a number of other medical conditions including but not limited to
vertigo Vertigo is a condition in which a person has the sensation that they are moving, or that objects around them are moving, when they are not. Often it feels like a spinning or swaying movement. It may be associated with nausea, vomiting, perspira ...
. It can also be temporarily disturbed by quick or prolonged
acceleration In mechanics, acceleration is the Rate (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...
, for example, riding on a
merry-go-round A carousel or carrousel (mainly North American English), merry-go-round (International English), or galloper (British English) is a type of amusement ride consisting of a rotating circular platform with seats for riders. The seats are tradit ...
. Blows can also affect equilibrioreception, especially those to the side of the head or directly to the ear. Most
astronaut An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a List of human spaceflight programs, human spaceflight program to serve as a commander or crew member of a spa ...
s find that their sense of balance is impaired when in orbit because they are in a constant state of
weightlessness Weightlessness is the complete or near-complete absence of the sensation of weight, i.e., zero apparent weight. It is also termed zero g-force, or zero-g (named after the g-force) or, incorrectly, zero gravity. Weight is a measurement of the fo ...
. This causes a form of
motion sickness Motion sickness occurs due to a difference between actual and expected motion. Symptoms commonly include nausea, vomiting, cold sweat, headache, dizziness, tiredness, loss of appetite, and increased salivation. Complications may rarely include ...
called
space adaptation syndrome Space adaptation syndrome (SAS) or space sickness is a condition experienced by as many as half of all space travelers during their adaptation to weightlessness once in orbit. It is the opposite of terrestrial motion sickness since it occurs whe ...
.


System overview

This overview also explains acceleration as its processes are interconnected with balance.


Mechanical

There are five
sensory organs A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of stimuli. Although, in some cultures, five human senses were traditionally identified as s ...
innervated A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called ...
by the
vestibular nerve The vestibular nerve is one of the two branches of the vestibulocochlear nerve (the cochlear nerve being the other). In humans the vestibular nerve transmits sensory information from vestibular hair cells located in the two otolith organs (the u ...
; three
semicircular canals The semicircular canals are three semicircular interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the lateral, anterior and posterior semicircular canals. They are the part of the bony labyrinth, ...
( Horizontal SCC, Superior SCC, Posterior SCC) and two
otolith An otolith (, ' ear + , ', a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle (ear), utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule ...
organs (
saccule The saccule (Latin: sacculus) is a bed of sensory cells in the inner ear that detects linear acceleration and head tilting in the vertical plane, and converts these vibrations into electrical impulses to be interpreted by the brain. When the he ...
and utricle). Each semicircular canal (SSC) is a thin tube that doubles in thickness briefly at a point called
osseous ampullae The semicircular canals are three semicircular interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the lateral, anterior and posterior semicircular canals. They are the part of the bony labyrinth, ...
. At their center-base, each contains an
ampullary cupula The ampullary cupula, or cupula, is a structure in the vestibular system, providing the sense of spatial orientation. The cupula is located within the ampullae of each of the three semicircular canals. Part of the crista ampullaris, the cupula h ...
. The cupula is a gelatin bulb connected to the
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 cel ...
of hair cells, affected by the relative movement of the
endolymph Endolymph is the fluid contained in the membranous labyrinth of the inner ear. The major cation in endolymph is potassium, with the values of sodium and potassium concentration in the endolymph being 0.91  mM and 154  mM, respectively. ...
it is bathed in. Since the cupula is part of the
bony labyrinth The bony labyrinth (also osseous labyrinth or otic capsule) is the rigid, bony outer wall of the inner ear in the temporal bone. It consists of three parts: the vestibule, semicircular canals, and cochlea. These are cavities hollowed out of the ...
, it rotates along with actual head movement, and by itself without the endolymph, it cannot be stimulated and therefore, could not detect movement. Endolymph follows the rotation of the canal; however, due to
inertia Inertia is the natural tendency of objects in motion to stay in motion and objects at rest to stay at rest, unless a force causes the velocity to change. It is one of the fundamental principles in classical physics, and described by Isaac Newto ...
its movement initially lags behind that of the bony labyrinth. The delayed movement of the endolymph bends and activates the cupula. When the cupula bends, the connected stereocilia bend along with it, activating chemical reactions in the hair cells surrounding
crista ampullaris The crista ampullaris is the sensory organ of rotation. They are found in the ampullae of each of the semicircular canals of the inner ear, meaning that there are three pairs in total. The function of the crista ampullaris is to sense angular a ...
and eventually create
action potentials An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific cell rapidly rises and falls. ...
carried by the vestibular nerve signaling to the body that it has moved in space. After any extended rotation, the endolymph catches up to the canal and the cupula returns to its upright position and resets. When extended rotation ceases, however, endolymph continues, (due to inertia) which bends and activates the cupula once again to signal a change in movement. Pilots doing long banked turns begin to feel upright (no longer turning) as endolymph matches canal rotation; once the pilot exits the turn the cupula is once again stimulated, causing the feeling of turning the other way, rather than flying straight and level. The horizontal SCC handles head rotations about a vertical axis (e.g. looking side to side), the superior SCC handles head movement about a lateral axis (e.g. head to shoulder), and the posterior SCC handles head rotation about a rostral-caudal axis (e.g. nodding). SCC sends adaptive signals, unlike the two otolith organs, the saccule and utricle, whose signals do not adapt over time. A shift in the
otolithic membrane The otolithic membrane is a fibrous structure located in the vestibular system of the inner ear. It plays a critical role in the brain's interpretation of equilibrium. The membrane serves to determine if the body or the head is tilted, in addition ...
that stimulates the cilia is considered the state of the body until the cilia are once again stimulated. For example, lying down stimulates cilia and standing up stimulates cilia, however, for the time spent lying the signal that you are lying remains active, even though the membrane resets. Otolithic organs have a thick, heavy gelatin membrane that, due to inertia (like endolymph), lags behind and continues ahead past the
macula The macula (/ˈmakjʊlə/) or macula lutea is an oval-shaped pigmented area in the center of the retina of the human eye and in other animals. The macula in humans has a diameter of around and is subdivided into the umbo, foveola, foveal avas ...
it overlays, bending and activating the contained cilia. Utricle responds to linear accelerations and head-tilts in the horizontal plane (head to shoulder), whereas
saccule The saccule (Latin: sacculus) is a bed of sensory cells in the inner ear that detects linear acceleration and head tilting in the vertical plane, and converts these vibrations into electrical impulses to be interpreted by the brain. When the he ...
responds to linear accelerations and head-tilts in the vertical plane (up and down). Otolithic organs update the brain on the head-location when not moving; SCC update during movement.
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. Contrasting with stereocilia, which are numerous, there is only one kinocilium on each hair cell. The kinocilium can ...
are the longest stereocilia and are positioned (one per 40-70 regular cilia) at the end of the bundle. If stereocilia go towards kinocilium,
depolarization In biology, depolarization or hypopolarization is a change within a cell (biology), cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolar ...
occurs, causing more
neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...
s, and more vestibular nerve firings, as compared to when stereocilia tilt away from kinocilium ( hyperpolarization, less neurotransmitter, less firing).


Neural

First order
vestibular nuclei The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve located in the brainstem. In Terminologia Anatomica, they are grouped in both the pons and the medulla in the brainstem The brainstem (or brain stem) is the poste ...
(VN) project to
lateral vestibular nucleus The lateral vestibular nucleus (Deiters's nucleus) is the continuation upward and lateralward of the Principal sensory nucleus of trigeminal nerve, principal nucleus, and in it terminate many of the ascending branches of the vestibular nerve. Stru ...
(IVN), medial vestibular nucleus (MVN), and
superior vestibular nucleus The superior vestibular nucleus ( Bechterew's nucleus) is the dorso-lateral part of the vestibular nucleus and receives collaterals and terminals from the ascending branches of the vestibular nerve. Sends uncrossed fibers to cranial nerve 3 and ...
(SVN). The
inferior cerebellar peduncle The inferior cerebellar peduncle is formed by fibers of the restiform body that join with fibers from the much smaller juxtarestiform body. The inferior cerebellar peduncle is the smallest of the three cerebellar peduncles. The upper part of t ...
is the largest center through which balance information passes. It is the area of integration between
proprioceptive Proprioception ( ) is the sense of self-movement, force, and body position. Proprioception is mediated by proprioceptors, a type of sensory receptor, located within muscles, tendons, and joints. Most animals possess multiple subtypes of propri ...
, and vestibular inputs, to aid in unconscious maintenance of balance and posture. The
inferior olivary nucleus The inferior olivary nucleus (ION) is a structure found in the medulla oblongata underneath the superior olivary nucleus.Gado, Thomas A. Woolsey; Joseph Hanaway; Mokhtar H. (2003). The brain atlas a visual guide to the human central nervous syste ...
aids in complex motor tasks by encoding coordinating timing sensory information; this is decoded and acted upon in the
cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...
. The
cerebellar vermis The cerebellar vermis (from Latin ''vermis,'' "worm") is located in the medial, cortico-nuclear zone of the cerebellum, which is in the posterior cranial fossa, posterior fossa of the cranium. The primary fissure in the vermis curves ventrolatera ...
has three main parts. The vestibulocerebellum regulates eye movements by the integration of visual info provided by the
superior colliculus In neuroanatomy, the superior colliculus () is a structure lying on the tectum, roof of the mammalian midbrain. In non-mammalian vertebrates, the Homology (biology), homologous structure is known as the optic tectum or optic lobe. The adjective f ...
and balance information. The
spinocerebellum The anatomy of the cerebellum can be viewed at three levels. At the level of gross anatomy, the cerebellum consists of a tightly folded and crumpled layer of Cerebellar cortex, cortex, with white matter underneath, several deep nuclei embedded i ...
integrates visual, auditory, proprioceptive, and balance information to act out body and limb movements. It receives input from the
trigeminal nerve In neuroanatomy, the trigeminal nerve (literal translation, lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for Sense, sensation in the face and motor functions ...
, dorsal column (of the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...
),
midbrain The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum. It is functionally associated with vision, hearing, mo ...
,
thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...
,
reticular formation The reticular formation is a set of interconnected nuclei in the brainstem that spans from the lower end of the medulla oblongata to the upper end of the midbrain. The neurons of the reticular formation make up a complex set of neural networks ...
and vestibular nuclei ( medulla) outputs. Lastly, the cerebrocerebellum plans, times, and initiates movement after evaluating sensory input from, primarily, motor cortex areas, via
pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other mammals, lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of ...
and cerebellar
dentate nucleus The dentate nucleus refer to a pair of deep cerebellar nuclei deep within the white matter of the cerebellum of the brain with a dentate – tooth-like or serrated – edge. The dentate forms the largest pathway between the cerebellum and the r ...
. It outputs to the thalamus,
motor cortex The motor cortex is the region of the cerebral cortex involved in the planning, motor control, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately ...
areas, and
red nucleus The red nucleus or nucleus ruber is a structure in the rostral midbrain involved in motor coordination. The red nucleus is pale pink, which is believed to be due to the presence of iron in at least two different forms: hemoglobin and ferritin. ...
. The flocculonodular lobe is a cerebellar lobe that helps maintain body equilibrium by modifying
muscle tone In physiology, medicine, and anatomy, muscle tone (residual muscle tension or tonus) is the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state.O’Sullivan, S. B. (2007) ...
(the continuous and passive muscle contractions). MVN and IVN are in the medulla, LVN and SVN are smaller and in pons. SVN, MVN, and IVN ascend within the
medial longitudinal fasciculus The medial longitudinal fasciculus (MLF) is a prominent bundle of nerve fibres which pass within the ventral/anterior portion of periaqueductal gray of the mesencephalon (midbrain). It contains the interstitial nucleus of Cajal, responsible ...
. LVN descend the spinal cord within the lateral vestibulospinal tract and ends at the
sacrum The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...
. MVN also descend the spinal cord, within the
medial vestibulospinal tract The medial vestibulospinal tract is one of the descending spinal tracts of the ventromedial funiculus of the spinal cord. It is found only in the cervical spine and above. The medial part of the vestibulospinal tract is the smaller part, and is pr ...
, ending at lumbar 1. The
thalamic reticular nucleus The thalamic reticular nucleus is part of the ventral thalamus that forms a capsule around the thalamus laterally. However, recent evidence from mice and fish question this statement and define it as a dorsal thalamic structure. It is separated fro ...
distributes information to various other thalamic nuclei, regulating the flow of information. It is speculatively able to stop signals, ending transmission of unimportant info. The thalamus relays info between pons (cerebellum link), motor cortices, and insula. The insula is also heavily connected to motor cortices; the insula is likely where balance is likely brought into perception. The oculomotor nuclear complex refers to fibers going to
tegmentum The tegmentum (from Latin for "covering") is a general area within the brainstem. The tegmentum is the ventral part of the midbrain and the tectum is the dorsal part of the midbrain. It is located between the ventricular system and distinctive b ...
(eye movement), red nucleus (
gait Gait is the pattern of Motion (physics), movement of the limb (anatomy), limbs of animals, including Gait (human), humans, during Animal locomotion, locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on s ...
(natural limb movement)),
substantia nigra The substantia nigra (SN) is a basal ganglia structure located in the midbrain that plays an important role in reward and movement. ''Substantia nigra'' is Latin for "black substance", reflecting the fact that parts of the substantia nigra a ...
(reward), and
cerebral peduncle The cerebral peduncles (In Latin, ''ped-'' means 'foot'.) are the two stalks that attach the cerebrum to the brainstem. They are structures at the front of the midbrain which arise from the ventral pons and contain the large ascending (sensor ...
(motor relay). Nucleus of Cajal are one of the named oculomotor nuclei, they are involved in eye movements and reflex gaze coordination. The
abducens nerve The abducens nerve or abducent nerve, also known as the sixth cranial nerve, cranial nerve VI, or simply CN VI, is a cranial nerve in humans and various other animals that controls the movement of the lateral rectus muscle, one of the extraocula ...
solely innervates the
lateral rectus muscle The lateral rectus muscle is a muscle on the lateral side of the eye in the orbit. It is one of six extraocular muscles that control the movements of the eye. The lateral rectus muscle is responsible for lateral movement of the eyeball, specif ...
of the eye, moving the eye with the
trochlear nerve The trochlear nerve (), ( lit. ''pulley-like'' nerve) also known as the fourth cranial nerve, cranial nerve IV, or CN IV, is a cranial nerve that innervates a single muscle - the superior oblique muscle of the eye (which operates through the pu ...
. The trochlear solely innervates the
superior oblique muscle The superior oblique muscle or obliquus oculi superior is a fusiform muscle originating in the upper, medial side of the orbit (anatomy), orbit (i.e. from beside the nose) which abducts, depresses and internally rotates the eye. It is the only e ...
of the eye. Together, trochlear and abducens contract and relax to simultaneously direct the pupil towards an angle and depress the globe on the opposite side of the eye (e.g. looking down directs the pupil down and depresses (towards the brain) the top of the globe). The pupil is not only directed, but often rotated, by these muscles. (See
visual system The visual system is the physiological basis of visual perception (the ability to perception, detect and process light). The system detects, phototransduction, transduces and interprets information concerning light within the visible range to ...
) The thalamus and superior colliculus are connected via the
lateral geniculate nucleus In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, Anatomical ter ...
. The superior colliculus (SC) is the topographical map for balance and quick orienting movements with primarily visual inputs. SC integrates multiple senses.


Other animals

Some animals have better equilibrioception than humans; for example, a
cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...
uses its
inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...
and
tail The tail is the elongated section at the rear end of a bilaterian animal's body; in general, the term refers to a distinct, flexible appendage extending backwards from the midline of the torso. In vertebrate animals that evolution, evolved to los ...
to walk on a thin
fence A fence is a structure that encloses an area, typically outdoors, and is usually constructed from posts that are connected by boards, wire, rails or net (textile), netting. A fence differs from a wall in not having a solid foundation along its ...
. Equilibrioception in many marine animals is done with an entirely different organ, the
statocyst The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, ctenophorans, echinoderms, cephalopods, crustaceans, and gastropods, A similar structure is also found in '' Xenoturbella''. T ...
, which detects the position of tiny
calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...
stones to determine which way is "up".


In plants

Plants could be said to exhibit a form of equilibrioception, in that when rotated from their normal attitude the stems grow in the direction that is upward (away from gravity) while their roots grow downward (in the direction of gravity). This phenomenon is known as
gravitropism Gravitropism (also known as geotropism) is a coordinated process of differential growth by a plant in response to gravity pulling on it. It also occurs in fungi. Gravity can be either "artificial gravity" or natural gravity. It is a general feat ...
and it has been shown that, for example, poplar stems can detect reorientation and inclination.


See also

*
Proprioception Proprioception ( ) is the sense of self-movement, force, and body position. Proprioception is mediated by proprioceptors, a type of sensory receptor, located within muscles, tendons, and joints. Most animals possess multiple subtypes of propri ...
*
Vertigo Vertigo is a condition in which a person has the sensation that they are moving, or that objects around them are moving, when they are not. Often it feels like a spinning or swaying movement. It may be associated with nausea, vomiting, perspira ...


References


External links

{{Authority control Vestibular system Sensory systems Motor control