The vestibulospinal tract is a

neural tract A nerve tract is a bundle of nerve fibers (axons) connecting nuclei of the central nervous system. In the peripheral nervous system this is known as a nerve, and has associated connective tissue. The main nerve tracts in the central nervous syste ...

in the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

. Specifically, it is a component of the

extrapyramidal system In anatomy, the extrapyramidal system is a part of the motor system network causing involuntary actions. The system is called ''extrapyramidal'' to distinguish it from the tracts of the motor cortex that reach their targets by traveling through t ...

and is classified as a component of the medial pathway. Like other descending motor pathways, the vestibulospinal fibers of the tract relay information from nuclei to motor neurons. The

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. Structure Path The fibers of the vestibular nerve ...

receive information through the

vestibulocochlear nerve The vestibulocochlear nerve or auditory vestibular nerve, also known as the eighth cranial nerve, cranial nerve VIII, or simply CN VIII, is a cranial nerve that transmits sound and equilibrium (balance) information from the inner ear to the bra ...

about changes in the orientation of the head. The nuclei relay motor commands through the vestibulospinal tract. The function of these motor commands is to alter muscle tone, extend, and change the position of the limbs and head with the goal of supporting posture and maintaining balance of the body and head.

Classification

The vestibulospinal tract is part of the "extrapyramidal system" of the central nervous system. In

human anatomy The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body. It comprises a he ...

, the extrapyramidal system is a

neural network A neural network is a network or circuit of biological neurons, or, in a modern sense, an artificial neural network, composed of artificial neurons or nodes. Thus, a neural network is either a biological neural network, made up of biological ...

located in the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

that is part of the

motor system The motor system is the set of central and peripheral structures in the nervous system that support motor functions, i.e. movement. Peripheral structures may include skeletal muscles and neural connections with muscle tissues. Central structur ...

involved in the coordination of movement. The system is called "extrapyramidal" to distinguish it from the tracts of the motor cortex that reach their targets by traveling through the "

pyramids A pyramid (from el, πυραμίς ') is a structure whose outer surfaces are triangular and converge to a single step at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilate ...

" of the

medulla Medulla or Medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ovary * Medulla of t ...

. The pyramidal pathways, such as

corticospinal The pyramidal tracts include both the corticobulbar tract and the corticospinal tract. These are aggregations of efferent nerve fibers from the upper motor neurons that travel from the cerebral cortex and terminate either in the brainstem (''co ...

and some

corticobulbar In neuroanatomy, the corticobulbar (or corticonuclear) tract is a two-neuron white matter motor pathway connecting the motor cortex in the cerebral cortex to the medullary pyramids, which are part of the brainstem's medulla oblongata (also called ...

tracts, may directly innervate motor neurons of the spinal cord or brainstem. This is seen in anterior (ventral) horn cells or certain cranial nerve nuclei. Whereas the extrapyramidal system centers around the modulation and regulation through indirect control of anterior (ventral) horn cells. The extrapyramidal subcortical nuclei include the substantia nigra, caudate, putamen, globus pallidus, thalamus, red nucleus and subthalamic nucleus. The traditional thought was that the extrapyramidal system operated entirely independently of the pyramidal system. However, more recent research has provided a greater understanding of the integration of motor control. Motor control from both the pyramidal and extrapyramidal systems have extensive feedback loops and are heavily interconnected with each other. A more appropriate classification of motor nuclei and tracts would be by their functions. When broken down by function there are two major pathways: medial and lateral. The medial pathway helps control gross movements of the proximal limbs and trunk. The lateral pathway helps control precise movement of the distal portion of limbs. The vestibulospinal tract, as well as tectospinal and reticulospinal tracts are examples of components of the medial pathway.

Function

The vestibulospinal tract is part of the

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 movement with balance. Together with the cochlea, a part of the auditory system, it constitutes ...

in the CNS. The primary role of the vestibular system is to maintain head and eye coordination, upright posture and balance, and conscious realization of spatial orientation and motion. The vestibular system is able to respond correctly by recording sensory information from hairs cells in the

labyrinth In Greek mythology, the Labyrinth (, ) was 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 ...

of the inner ear. Then the nuclei receiving these signals project out to the

extraocular muscles The extraocular muscles (extrinsic ocular muscles), are the seven extrinsic muscles of the human eye. Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye and the ot ...

, spinal cord, and cerebral cortex to execute these functions. One of these projections, the vestibulospinal tract, is responsible for upright posture and head stabilization. When the vestibular sensory neurons detect small movements of the body, the vestibulospinal tract commands motor signals to specific muscles to counteract these movements and re-stabilize the body. The vestibulospinal tract is an

upper motor neuron Upper motor neurons (UMNs) is a term introduced by William Gowers in 1886. They are found in the cerebral cortex and brainstem and carry information down to activate interneurons and lower motor neurons, which in turn directly signal muscles t ...

tract consisting of two sub-pathways: :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 ...

projects bilaterally from the

medial vestibular nucleus The medial vestibular nucleus (Schwalbe nucleus) is one of the vestibular nuclei. It is located in the medulla oblongata. Lateral vestibulo-spinal tract (lateral vestibular nucleus “Deiters”)- via ventrolateral medulla and spinal cord to ventr ...

within the

medial longitudinal fasciculus The medial longitudinal fasciculus (MLF) is an area of crossed over tracts, on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem. They are made up of both ascending and descending fibers that ari ...

to the ventral horns in the upper cervical cord (C6 vertebra). It promotes stabilization of head position by innervating the neck muscles, which helps with head coordination and eye movement. Its function is similar to that of the

tectospinal tract In humans, the tectospinal tract (or colliculospinal tract) is a nerve tract that coordinates head and eye movements. This tract is part of the extrapyramidal system and connects the midbrain tectum, and cervical regions of the spinal cord. It ...

. :The

lateral vestibulospinal tract The lateral vestibulospinal tract is one of the descending spinal tracts of the ventromedial funiculus. The lateral part of the vestibulospinal tract is the major portion and is composed of fibers originating in the lateral, superior, and inferior ...

provides excitatory signals to

interneurons Interneurons (also called internuncial neurons, relay neurons, association neurons, connector neurons, intermediate neurons or local circuit neurons) are neurons that connect two brain regions, i.e. not direct motor neurons or sensory neurons. In ...

, which relay the signal to the motor neurons in antigravity muscles. These antigravity muscles are extensor muscles in the legs that help maintain upright and balanced posture.

Anatomy

Lateral vestibulospinal tract

The lateral vestibulospinal tract is a group of descending extrapyramidal motor neurons, or

efferent nerve fiber Efferent nerve fibers refer to axonal projections that ''exit'' a particular region; as opposed to afferent projections that ''arrive'' at the region. These terms have a slightly different meaning in the context of the peripheral nervous syste ...

s. This tract is found in the

lateral funiculus The most lateral of the bundles of the anterior nerve roots is generally taken as a dividing line that separates the anterolateral system into two parts. These are the anterior funiculus, between the anterior median fissure and the most lateral ...

, a bundle of

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

roots in the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

. The

originates in the

lateral vestibular nucleus The lateral vestibular nucleus (Deiters's nucleus) is the continuation upward and lateralward of the principal nucleus, and in it terminate many of the ascending branches of the vestibular nerve. Structure It consists of very large multipolar cel ...

or Deiters’ nucleus in the

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds 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 Va ...

. The Deiters' nucleus extends from pontomedullary junction to the level of

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 ...

nucleus in the

. Lateral vestibulospinal fibers descend uncrossed, or

ipsilateral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

, in the anterior portion of the

of the spinal cord. Fibers run down the total length of the spinal cord and terminate at the

of laminae VII and VIII. Additionally, some neurons terminate directly on the dendrites of

alpha motor neuron Alpha (α) motor neurons (also called alpha motoneurons), are large, multipolar lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their con ...

s in the same laminae.

Medial vestibulospinal tract

The medial vestibulospinal tract is a group of descending extrapyramidal motor neurons, or efferent fibers found in the

anterior funiculus In the spinal cord, the most lateral of the bundles of the ventral nerve roots is generally taken as a dividing line that separates the antero-lateral region into two parts: an anterior funiculus (or anterior column), between the anterior median ...

, a bundle of nerve roots in the spinal cord. The medial vestibulospinal tract originates in the

or Schwalbe's nucleus. The Schwalbe's nucleus extends from the rostral end of 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 syst ...

of the medulla oblongata to the caudal portion of the pons. Medial vestibulospinal fibers join with the ipsilateral and

contralateral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

, and descend in the anterior funiculus of the spinal cord. Fibers run down to the anterior funiculus to the cervical spinal cord segments and terminate on

neurons A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

of laminae VII and VIII. Unlike the lateral vestibulospinal tract, the medial vestibulospinal tract innervates muscles that support the head. As a result, medial vestibulospinal fibers run down only to the cervical segments of the cord.

Reflexes

The vestibulospinal

reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...

uses the vestibular organs as well as skeletal muscle in order to maintain balance, posture, and stability in an environment with gravity. These reflexes can be further broken down by timing into a dynamic reflex, static reflex or tonic reflex. It can also be categorized by the sensory input as either

canals Canals or artificial waterways are waterways or river engineering, engineered channel (geography), channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport watercraft, vehicles (e.g. ...

otolith An otolith ( grc-gre, ὠτο-, ' ear + , ', a stone), also called statoconium or otoconium or statolith, is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in the vestibular system of vertebrates. The sa ...

, or both. The term vestibulospinal reflex, is most commonly used when the sensory input evokes a response from the

muscular system The muscular system is an organ (anatomy), organ system consisting of skeletal muscle, skeletal, smooth muscle, smooth, and cardiac muscle, cardiac muscle. It permits movement of the body, maintains posture, and circulates blood throughout the bo ...

below the neck. These reflexes are important in the maintenance of

homeostasis In biology, homeostasis (British English, British also homoeostasis) Help:IPA/English, (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. Thi ...

Example of vestibulospinal reflex

# The head is tilted to one side which stimulates both the canals and the otoliths. # This movement stimulates 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 transmitted by vestibular hair cells located in the two otolith orga ...

as well as the

vestibular nucleus 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. Structure Path The fibers of the vestibular nerv ...

. # These impulses are transmitted down both the lateral and medial vestibulospinal tracts to the

. # The spinal cord induces extensor effects in the muscle on the side of the neck to which the head is bent, and flexor effects in the muscle in the side of the neck away from the direction of the displaced head.

Tonic labyrinthine reflex

The

tonic labyrinthine reflex The tonic labyrinthine reflex (TLR) is a primitive reflex found in newborn humans. With this reflex, tilting the head back while lying on the back causes the back to stiffen and even arch backwards, the legs to straighten, stiffen, and push togethe ...

(TLR) is a reflex that is present in newborn babies directly after birth and should be fully inhibited by 3.5 years. This reflex helps the baby master head and neck movements outside of the

womb The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...

as well as the concept of

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

. Increased muscle tone, development of the

proprioceptive Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense". Proprioception is mediated by proprioceptors, mechanosensory neurons ...

and vestibular senses and opportunities to practice with balance are all consequences of this reflex. During early childhood, the TLR matures into more developed vestibulospinal reflexes to help with posture, head alignment and balance. The

is found in two forms. # Forward: When the head bends forward, the whole body, arms, legs and torso curl together to form the

fetal position Fetal position (British English: also foetal) is the positioning of the body of a prenatal fetus as it develops. In this position, the back is curved, the head is bowed, and the limbs are bent and drawn up to the torso. A compact position is ...

. # Backwards: When the head is bent backward, the whole body, arms, legs and torso straighten and extend.

Righting reflex

The

righting reflex The righting reflex, also known as the labyrinthine righting reflex, is a reflex that corrects the orientation of the body when it is taken out of its normal upright position. It is initiated by the vestibular system, which detects that the body is ...

is another type of reflex. This reflex positions the head or body back into its "normal" position, in response to a change in head or body position. A common example of this reflex is the cat righting reflex, which allows them to orient themselves in order to land on their feet. This reflex is initiated by sensory information from the vestibular,

visual The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight (the ...

, and the

somatosensory In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), and pain. It i ...

systems and is therefore not only a vestibulospinal reflex.

Damage

A typical person sways from side to side when the eyes are closed. This is the result of the vestibulospinal reflex working correctly. When an individual sways to the left side, the left lateral vestibulospinal tract is activated to bring the body back to midline. Generally damage to the vestibulospinal system results in

ataxia Ataxia is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in eye movements. Ataxia is a clinical manifestation indicating dysfunction of ...

and postural instability. For example, if unilateral damage occurs to the

semicircular canal In mathematics (and more specifically geometry), a semicircle is a one-dimensional locus of points that forms half of a circle. The full arc of a semicircle always measures 180° (equivalently, radians, or a half-turn). It has only one line of ...

s or

, the person will likely sway to that side and fall when walking. This occurs because the healthy side "over powers" the weak side in a way that will cause the person to veer and fall towards the injured side. Potential early onset of damage can be witnessed through a positive

Romberg's test Romberg's test, Romberg's sign, or the Romberg maneuver is a test used in an exam of neurological function for balance, and also as a test for driving under the influence of an intoxicant. The exam is based on the premise that a person requires ...

. Patients with bilateral or unilateral vestibular system damage will likely regain postural stability over weeks and months through a process called vestibular compensation. This process is likely related to a greater reliance on other sensory information.

Current and future research

* Recent research has shown that damage to the medial vestibulospinal tract alters vestibular evoked myogenic potential in the

sternocleidomastoid muscle The sternocleidomastoid muscle is one of the largest and most superficial cervical muscles. The primary actions of the muscle are rotation of the head to the opposite side and flexion of the neck. The sternocleidomastoid is innervated by the access ...

(SCM), which are involved in head rotation. The vestibular evoked myogenic potential is an assessment of the sacculo-collic reflex and a test of function in otolithic organs. Also, lesions to the tract impair ascending efferent fiber signaling, which led to

nystagmus Nystagmus is a condition of involuntary (or voluntary, in some cases) eye movement. Infants can be born with it but more commonly acquire it in infancy or later in life. In many cases it may result in reduced or limited vision. Due to the invol ...

. * There has also been recent research to determine if there is a difference in vestibulospinal function when there is damage to the superior vestibular nerve as opposed to the inferior vestibular nerve and vice versa. They defined vestibulospinal function by ability to have proper posture, as well as by self reported dizziness. The results were determined by using the Sensory Organization Test (SOT) of the computerized dynamic posturography (CDP) as well as the dizziness handicap inventory (DHI). It was determined that subjects with damaged inferior spinal nerve performed worse on the posture test than the control group, but performed better than patients with superior vestibulo nerve damage. With this they determined that the superior vestibular nerve plays a larger role in balance than the inferior vestibulo nerve but that they both play a role. In terms of the DHI it was concluded that there was no difference between the patients with the two different impairments. *Vestibular compensation after unilateral or bilateral vestibular system damage can be accomplished by sensory addition and sensory substitution. Sensory substitution occurs when any remaining vestibular function, vision, or light touch of a stable surface substitute for the lost function. Postural sway and gait ataxia can be reduced by augmenting sensory information for balance control. Recent research has shown that as little as 100 grams of light touch of a fingertip can provide enough sensory reference to reduce sway and ataxia during

gait Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. Di ...

References

External links

* {{Auditory and vestibular pathways Spinal cord tracts Motor system