Dorsal spinocerebellar tract

The dorsal spinocerebellar tract (posterior spinocerebellar tract, Flechsig's fasciculus, Flechsig's tract) conveys proprioceptive information from proprioceptors in the skeletal muscles and joints to the cerebellum.[1]

It is part of the somatosensory system and runs in parallel with the ventral spinocerebellar tract. It carries proprioceptive information from muscle spindles and Golgi tendon organs of ipsilateral part of trunk and lower limb. Proprioceptive information is taken to the spinal cord via central processes of dorsal root ganglia (first order neurons). These central processes travel through the dorsal horn where they synapse with second order neurons of Clarke's nucleus. Axon fibers from Clarke's Nucleus convey this proprioceptive information in the spinal cord in the peripheral region of the funiculus posterior ipsilaterally. The fibers continue to course through the medulla oblongata of the brainstem, at which point they pass through the inferior cerebellar peduncle and into the cerebellum, where unconscious proprioceptive information is processed.

This tract involves two neurons and ends up on the same side of the body.

The terms Flechsig's fasciculus and Flechsig's tract are named after German neuroanatomist, psychiatrist and neuropathologist Paul Flechsig.

Dorsal spinocerebellar tract
Spinal cord tracts - English
Dorsal spinocerebellar tract is labeled in blue at right.
Gray672
Diagram of the principal fasciculi of the spinal cord. (Dorsal spinocerebellar fasciculus visible at center left.)
Details
Identifiers
LatinTractus spinocerebellaris posterior,
tractus spinocerebellaris dorsalis
TAA14.1.02.227
A14.1.04.132
FMA73950
Anatomical terminology

References

  1. ^ Adel K. Afifi Functional Neuroanatomy pag.51 ISBN 970-10-5504-7

External links

Anatomy of the cerebellum

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 cortex, with white matter underneath, several deep nuclei embedded in the white matter, and a fluid-filled ventricle in the middle. At the intermediate level, the cerebellum and its auxiliary structures can be broken down into several hundred or thousand independently functioning modules or "microzones". At the microscopic level, each module consists of the same small set of neuronal elements, laid out with a highly stereotyped geometry.

Brown-Séquard syndrome

Brown-Séquard syndrome (also known as Brown-Séquard's hemiplegia, Brown-Séquard's paralysis, hemiparaplegic syndrome, hemiplegia et hemiparaplegia spinalis, or spinal hemiparaplegia) is caused by damage to one half of the spinal cord, resulting in paralysis and loss of proprioception on the same (or ipsilateral) side as the injury or lesion, and loss of pain and temperature sensation on the opposite (or contralateral) side as the lesion. It is named after physiologist Charles-Édouard Brown-Séquard, who first described the condition in 1850.

Cerebellar peduncle

Cerebellar peduncles connect the cerebellum to the brain stem. There are six cerebellar peduncles in total, three on each side:

Superior cerebellar peduncle is a paired structure of white matter that connects the cerebellum to the mid-brain.

Middle cerebellar peduncles connect the cerebellum to the pons and are composed entirely of centripetal fibers.

Inferior cerebellar peduncle is a thick rope-like strand that occupies the upper part of the posterior district of the medulla oblongata.The peduncles form the lateral border of the fourth ventricle, and form a distinctive diamond – the middle peduncle forming the central corners of the diamond, while the superior and inferior peduncles form the superior and inferior edges, respectively.

Inferior cerebellar peduncle

The upper part of the posterior district of the medulla oblongata is occupied by the inferior cerebellar peduncle, a thick rope-like strand situated between the lower part of the fourth ventricle and the roots of the glossopharyngeal and vagus nerves.

Each cerebellar inferior peduncle connects the spinal cord and medulla oblongata with the cerebellum, and comprises the juxtarestiform body and restiform body.

Important fibers running through the inferior cerebellar peduncle include the dorsal spinocerebellar tract and axons from the inferior olivary nucleus, among others.

Interposed nucleus

The interposed nucleus is part of the deep cerebellar complex and is composed of the globose nucleus and the emboliform nucleus. It is located in the roof (dorsal aspect) of the fourth ventricle, lateral to the fastigial nucleus. It receives its afferent supply from the anterior lobe of the cerebellum and sends output via the superior cerebellar peduncle to the red nucleus.

The interposed nucleus is located in the paravermis of the cerebellum. It receives input from the ipsilateral posterior external arcuate fibers (cuneocerebellar tract) and the dorsal spinocerebellar tract, which originate in the accessory cuneate nucleus and the posterior thoracic nucleus, respectively. The interposed nucleus is responsible for coordinating agonist/antagonist muscle pairs, and therefore a lesion in this area causes tremor.

The interposed nucleus is smaller than the dentate but larger than the fastigial nucleus.

Posterior external arcuate fibers

The posterior external arcuate fibers (dorsal external arcuate fibers) take origin in the accessory cuneate nucleus; they pass to the inferior peduncle of the same side.

It carries proprioceptive information from the upper limbs and neck. It is an analogue to the dorsal spinocerebellar tract for the upper limbs. In this context, the "cuneo-" derives from the accessory cuneate nucleus, not the cuneate nucleus. (The two nuclei are related in space, but not in function.)

The term "cuneocerebellar tract" is sometimes used to collectively refer to the posterior external arcuate fibers.The term "cuneocerebellar tract" is also used to describe an exteroceptive and proprioceptive components that take origin in the gracile and cuneate nuclei; they pass to the inferior peduncle of the same side.It is uncertain whether fibers are continued directly from the gracile and cuneate fasciculi into the inferior peduncle.

Posterior thoracic nucleus

The posterior thoracic nucleus, (Clarke's column, column of Clarke, dorsal nucleus, nucleus dorsalis of Clarke) is a group of interneurons found in the medial part of lamina VII, also known as the intermediate zone, of the spinal cord. It is mainly located from the thoracic vertebra T8 to lumbar L3-L4 levels and is an important structure for proprioception of the lower limb.

Proprioception

Proprioception ( PROH-pree-o-SEP-shən), is the sense of the relative position of one's own parts of the body and strength of effort being employed in movement. It is sometimes described as the "sixth sense".In humans, it is provided by proprioceptors in skeletal striated muscles (muscle spindles) and tendons (Golgi tendon organ) and the fibrous membrane in joint capsules. It is distinguished from exteroception, by which one perceives the outside world, and interoception, by which one perceives pain, hunger, etc., and the movement of internal organs.

The brain integrates information from proprioception and from the vestibular system into its overall sense of body position, movement, and acceleration. The word kinesthesia or kinæsthesia (kinesthetic sense) strictly means movement sense, but has been used inconsistently to refer either to proprioception alone or to the brain's integration of proprioceptive and vestibular inputs.

Proprioception has also been described in other animals such as vertebrates, and in some invertebrates such as arthropods. More recently proprioception has also been described in flowering land plants (angiosperms).

Spinal cord

The spinal cord is a long, thin, tubular structure made up of nervous tissue, that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord that contains cerebrospinal fluid. The brain and spinal cord together make up the central nervous system (CNS). In humans, the spinal cord begins at the occipital bone where it passes through the foramen magnum, and meets and enters the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) in men and around 43 cm (17 in) long in women. Also, the spinal cord has a varying width, ranging from 13 mm (1⁄2 in) thick in the cervical and lumbar regions to 6.4 mm (1⁄4 in) thick in the thoracic area.

The spinal cord functions primarily in the transmission of nerve signals from the motor cortex to the body, and from the afferent fibers of the sensory neurons to the sensory cortex. It is also a center for coordinating many reflexes and contains reflex arcs that can independently control reflexes. It is also the location of groups of spinal interneurons that make up the neural circuits known as central pattern generators. These circuits are responsible for controlling motor instructions for rhythmic movements such as walking.

Spinocerebellar tract

The spinocerebellar tract is a nerve tract originating in the spinal cord and terminating in the same side (ipsilateral) of the cerebellum.

Subacute combined degeneration of spinal cord

Subacute combined degeneration of spinal cord, also known as Lichtheim's disease, refers to degeneration of the posterior and lateral columns of the spinal cord as a result of vitamin B12 deficiency (most common), vitamin E deficiency, and copper deficiency. It is usually associated with pernicious anemia.

Ventral spinocerebellar tract

The ventral spinocerebellar tract conveys proprioceptive information from the body to the cerebellum. It is part of the somatosensory system and runs in parallel with the dorsal spinocerebellar tract. Both these tracts involve two neurons.

The ventral spinocerebellar tract will cross to the opposite side of the body first in the spinal cord as part of the anterior white commissure and then cross again to end in the cerebellum (referred to as a "double cross"), as compared to the dorsal spinocerebellar tract, which does not decussate, or cross sides, at all through its path.

The ventral tract (under L2/L3) gets its proprioceptive/fine touch/vibration information from a first order neuron, with its cell body in a dorsal ganglion. The axon runs via the fila radicularia to the dorsal horn of the grey matter. There it makes a synapse with the dendrites of two neurons: they send their axons bilaterally to the ventral border of the lateral funiculi. The ventral spinocerebellar tract then enters the cerebellum via the superior cerebellar peduncle. This is in contrast with the dorsal spinocerebellar tract (C8 - L2/L3), which only has 1 unilateral axon that has its cell body in Clarke's column (only at the level of C8 - L2/L3). The fibers of the ventral spinocerebellar tract then eventually enter the cerebellum via the superior cerebellar peduncle.

Originates from ventral horn at lumbosacral spinal levels. Axons first cross midline in the spinal cord and run in the ventral border of the lateral funiculi. These axons ascend to the pons where they join the superior cerebellar peduncle to enter the cerebellum. Once in the deep white matter of the cerebellum, the axons recross the midline, give off collaterals to the globose and emboliform nuclei, and terminate in the cortex of the anterior lobe and vermis of the posterior lobe.

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