Vestibulospinal tract

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Vestibulospinal tract
Spinal cord tracts - English.svg
Vestibulospinal tract is labeled, in red at bottom left.
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Diagram of the principal fasciculi of the spinal cord. (Vestibulospinal fasciculus labeled at bottom right.)
Details
Identifiers
Latin tractus vestibulospinalis
NeuroLex ID birnlex_1643
FMA 72646
Anatomical terms of neuroanatomy

The vestibulospinal tract is a nerve tract in the central nervous system. Specifically, it is a component of the extrapyramidal system 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. [1] The vestibular nuclei receive information through the vestibulocochlear nerve 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. [1]

Contents

Classification

The vestibulospinal tract is part of the "extrapyramidal system" of the central nervous system. In human anatomy, the extrapyramidal system is a neural network located in the brain that is part of the motor system involved in the coordination of movement. [2] The system is called "extrapyramidal" to distinguish it from the tracts of the motor cortex that reach their targets by traveling through the "pyramids" of the medulla. The pyramidal pathways, such as corticospinal and some corticobulbar 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. [3]

Motor control from both the pyramidal and extrapyramidal systems have extensive feedback loops and are heavily interconnected with each other. [1] An 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. [1] The vestibulospinal tract, as well as tectospinal and reticulospinal tracts are examples of components of the medial pathway. [1]

Function

The vestibulospinal tract is part of the vestibular system 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 of the inner ear. Then the nuclei receiving these signals project out to the extraocular muscles, spinal cord, and cerebral cortex to execute these functions. [4]

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 tract consisting of two sub-pathways:

The medial vestibulospinal tract projects bilaterally from the medial vestibular nucleus within the medial longitudinal fasciculus to the ventral horns in the upper cervical cord (C6 vertebra). [5] 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.
The lateral vestibulospinal tract provides excitatory signals to interneurons, which relay the signal to the motor neurons in antigravity muscles. [6] These antigravity muscles are extensor muscles in the legs that help maintain upright and balanced posture.

Anatomy

Spinal cord
Medulla spinalis - Section - English.svg
Details
Identifiers
Latin medulla spinalis
NeuroLex ID birnlex_1643
FMA 72646
Anatomical terminology

Lateral vestibulospinal tract

The lateral vestibulospinal tract is a group of descending extrapyramidal motor neurons, or efferent nerve fibers. [2] This tract is found in the lateral funiculus, a bundle of nerve roots in the spinal cord. The lateral vestibulospinal tract originates in the lateral vestibular nucleus (Deiters’ nucleus) in the pons. [2] Deiters' nucleus extends from the pontomedullary junction to the level of the abducens nerve nucleus in the pons. [2]

Lateral vestibulospinal fibers descend uncrossed, or ipsilateral, in the anterior portion of the lateral funiculus of the spinal cord. [2] [7] Fibers run down the total length of the spinal cord and terminate at the interneurons of laminae VII and VIII. Additionally, some neurons terminate directly on the dendrites of alpha motor neurons in the same laminae. [2]

Medial vestibulospinal tract

The medial vestibulospinal tract is a group of descending extrapyramidal motor neurons, or efferent fibers found in the anterior funiculus, a bundle of nerve roots in the spinal cord. The medial vestibulospinal tract originates in the medial vestibular nucleus or Schwalbe's nucleus. [2] The Schwalbe's nucleus extends from the rostral end of the inferior olivary nucleus of the medulla oblongata to the caudal portion of the pons. [2]

Medial vestibulospinal fibers join with the ipsilateral and contralateral medial longitudinal fasciculus, and descend in the anterior funiculus of the spinal cord. [2] [7] Fibers run down to the anterior funiculus to the cervical spinal cord segments and terminate on neurons 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. [2]

Reflexes

The vestibulospinal reflex 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, otolith, or both. The term vestibulospinal reflex, is most commonly used when the sensory input evokes a response from the muscular system below the neck. These reflexes are important in the maintenance of homeostasis. [8]

Example of vestibulospinal reflex

  1. The head is tilted to one side which stimulates both the canals and the otoliths.
  2. This movement stimulates the vestibular nerve as well as the vestibular nucleus.
  3. These impulses are transmitted down both the lateral and medial vestibulospinal tracts to the spinal cord.
  4. 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 (TLR) is a reflex that is present in newborn babies directly after birth and should be fully inhibited by 3.5 years. [9] This reflex helps the baby master head and neck movements outside of the womb as well as the concept of gravity. Increased muscle tone, development of the proprioceptive 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. [10]

The tonic labyrinthine reflex is found in two forms.

  1. Forward: When the head bends forward, the whole body, arms, legs and torso curl together to form the fetal position.
  2. Backwards: When the head is bent backward, the whole body, arms, legs and torso straighten and extend.

Righting reflex

The righting reflex 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, and the somatosensory systems and is therefore not only a vestibulospinal reflex. [8]

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. [7] Generally damage to the vestibulospinal system results in ataxia and postural instability. [11] For example, if unilateral damage occurs to the vestibulocochlear nerve, lateral vestibular nucleus, semicircular canals or lateral vestibulospinal tract, 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. [6] Potential early onset of damage can be witnessed through a positive Romberg's test. [6] Patients with bilateral or unilateral vestibular system damage will likely regain postural stability over weeks and months through a process called vestibular compensation. [11] This process is likely related to a greater reliance on other sensory information.

Current and future research

See also

Related Research Articles

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<span class="mw-page-title-main">Medulla oblongata</span> Structure of the brain stem

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Articles related to anatomy include:

<span class="mw-page-title-main">Brainstem</span> Posterior part of the brain, adjoining and structurally continuous

The brainstem is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is continuous with the thalamus of the diencephalon through the tentorial notch, and sometimes the diencephalon is included in the brainstem.

<span class="mw-page-title-main">Trigeminal nerve</span> Cranial nerve responsible for the faces senses and motor functions

In neuroanatomy, the trigeminal nerve (lit. triplet nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves. Its name (trigeminal, from Latin tri- 'three' and -geminus 'twin') derives from each of the two nerves (one on each side of the pons) having three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory (or "cutaneous") functions. Adding to the complexity of this nerve is that autonomic nerve fibers as well as special sensory fibers (taste) are contained within it.

<span class="mw-page-title-main">Extrapyramidal system</span> Connection between brain and spinal cord

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 the pyramids of the medulla. The pyramidal tracts may directly innervate motor neurons of the spinal cord or brainstem, whereas the extrapyramidal system centers on the modulation and regulation of anterior (ventral) horn cells.

<span class="mw-page-title-main">Pyramidal tracts</span> The corticobulbar tract and the corticospinal tract

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 (corticobulbar) or spinal cord (corticospinal) and are involved in the control of motor functions of the body.

<span class="mw-page-title-main">Spinothalamic tract</span> Sensory pathway from the skin to the thalamus

The spinothalamic tract is a nerve tract in the anterolateral system in the spinal cord. This tract is an ascending sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the somatosensory cortex of the postcentral gyrus.

<span class="mw-page-title-main">Dorsal column–medial lemniscus pathway</span> Sensory spinal pathway

The dorsal column–medial lemniscus pathway (DCML) (also known as the posterior column-medial lemniscus pathway is the major sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception from the skin and joints. It transmits this information to the somatosensory cortex of the postcentral gyrus in the parietal lobe of the brain. The pathway receives information from sensory receptors throughout the body, and carries this in the gracile fasciculus and the cuneate fasciculus, tracts that make up the white matter dorsal columns of the spinal cord. At the level of the medulla oblongata, the fibers of the tracts decussate and are continued in the medial lemniscus, on to the thalamus and relayed from there through the internal capsule and transmitted to the somatosensory cortex. The name dorsal-column medial lemniscus comes from the two structures that carry the sensory information: the dorsal columns of the spinal cord, and the medial lemniscus in the brainstem.

<span class="mw-page-title-main">Medial longitudinal fasciculus</span> Nerve tracts in the brainstem

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 for oculomotor control, head posture, and vertical eye movement.

<span class="mw-page-title-main">Reticular formation</span> Spinal trigeminal nucleus

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 in the core of the brainstem. The reticular formation is made up of a diffuse net-like formation of reticular nuclei which is not well-defined. It may be seen as being made up of all the interspersed cells in the brainstem between the more compact and named structures.

<span class="mw-page-title-main">Rubrospinal tract</span> Part of the nervous system

The rubrospinal tract is one of the descending tracts of the spinal cord. It is a motor control pathway that originates in the red nucleus. It is a part of the lateral indirect extrapyramidal tract.

<span class="mw-page-title-main">Flocculonodular lobe</span> Lobe of the cerebellum

The flocculonodular lobe (vestibulocerebellum) is one of the lobes of the cerebellum. It is a small lobe consisting of the unpaired midline nodule and the two flocculi: one flocculus on either side of the nodule. The lobe is involved in maintaining posture and balance as well as coordinating head-eye movements.

<span class="mw-page-title-main">Vestibular nuclei</span>

The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve located in the brainstem.

<span class="mw-page-title-main">Lateral vestibular nucleus</span>

The lateral vestibular nucleus is the continuation upward and lateralward of the principal nucleus, and in it terminate many of the ascending branches of the vestibular nerve.

<span class="mw-page-title-main">Alpha motor neuron</span> Large lower motor neurons of the brainstem and spinal cord

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 contraction. Alpha motor neurons are distinct from gamma motor neurons, which innervate intrafusal muscle fibers of muscle spindles.

<span class="mw-page-title-main">Medial vestibulospinal tract</span>

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.

<span class="mw-page-title-main">Spinal cord</span> Part of the vertebral column in animals

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 cord is hollow and contains a structure called the central canal, which contains cerebrospinal fluid. The spinal cord is also covered by meninges and enclosed by the neural arches. Together, the brain and spinal cord make up the central nervous system.

<span class="mw-page-title-main">Blocq's disease</span> Loss of memory of specialized movements causing the inability to maintain an upright posture

Blocq's disease was first considered by Paul Blocq (1860–1896), who described this phenomenon as the loss of memory of specialized movements causing the inability to maintain an upright posture, despite normal function of the legs in the bed. The patient is able to stand up, but as soon as the feet are on the ground, the patient cannot hold himself upright nor walk; however when lying down, the subject conserved the integrity of muscular force and the precision of movements of the lower limbs. The motivation of this study came when a fellow student Georges Marinesco (1864) and Paul published a case of parkinsonian tremor (1893) due to a tumor located in the substantia nigra.

<span class="mw-page-title-main">Lateral vestibulospinal tract</span>

The lateral vestibulospinal tract is one of the descending spinal tracts of the ventromedial funiculus.

References

  1. 1 2 3 4 5 Martini, Frederic (2010). Anatomy & Physiology. Benjamin Cummings. ISBN   978-0-321-59713-7.
  2. 1 2 3 4 5 6 7 8 9 10 Afifi, Adel (1998). Functional Neuroanatomy . McGraw Hill. ISBN   978-0-07-001589-0.
  3. ↑ "Motor Systems" . Retrieved 2 November 2011.
  4. ↑ Voron, Stephen. "The Vestibular System". University of Utah School of Medicine. Retrieved 1 November 2011.
  5. ↑ Miselis, Dr. Richard. "Laboratory 12 : Tract Systems I". University of Pennsylvania School of Veterinary Medicine. Retrieved 1 November 2011.
  6. 1 2 3 "VESTIBULAR NUCLEI AND ABDUCENS NUCLEUS". Medical Neurosciences University of Wisconsin. Archived from the original on November 9, 2011. Retrieved 1 November 2011.
  7. 1 2 3 Bono, Christopher (2010). Spinal Cord Medicine. Demos Medical Publishing. ISBN   978-1-933864-19-8.
  8. 1 2 Hain, Timothy. "Postural, Vestibulospinal and Vestibulocollic Reflexes" . Retrieved 1 November 2011.
  9. ↑ "Primitive Reflexes and How They Effect Performance". Brain and Behaviour Enhancement. Retrieved 1 November 2011.
  10. ↑ Story, Sonia. "TLR: Tonic Labyrinthine Reflex". Brain Development Through Movement and Play. Retrieved 1 November 2011.
  11. 1 2 3 Horak, Fay (May 2009). "Postural Compensation for Vestibular Loss". Annals of the New York Academy of Sciences. 1164 (1): 76–81. Bibcode:2009NYASA1164...76H. doi:10.1111/j.1749-6632.2008.03708.x. PMC   3224857 . PMID   19645883.
  12. 1 2 Kim, Seonhye; Lee, Hak-Seung; Kim, Ji Soo (7 January 2010). "Medial vestibulospinal tract lesions impair sacculo-collic reflexes". Journal of Neurology. 257 (5): 825–832. doi:10.1007/s00415-009-5427-5. PMID   20054695. S2CID   20645277.
  13. 1 2 Kim, Seonhye; Kim, Hyo-Jung; Kim, Ji Soo (1 January 2011). "Impaired Sacculocollic Reflex in Lateral Medullary Infarction". Frontiers in Neurology. 2: 8. doi: 10.3389/fneur.2011.00008 . PMC   3041465 . PMID   21415908.
  14. ↑ McCaslin, DL (September 2011). "The influence of unilateral saccular impairment on functional balance performance and self-report dizziness". Journal of the American Academy of Audiology. 22 (8): 542–549. doi:10.3766/jaaa.22.8.6. PMID   22031678.
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