The spinocerebellar tracts are

nerve 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 ...

s originating in the spinal cord and terminating in the same side ( ipsilateral) of the

cerebellum The cerebellum (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 or even larger. In humans, the cerebel ...

. The two main tracts are the dorsal spinocerebellar tract, and the ventral spinocerebellar tract. Both of these tracts are located in the peripheral region of the lateral funiculi (white matter columns). They carry proprioceptive, and cutaneous information to the cerebellum, where movement can be coordinated.

Origins of proprioceptive information

Proprioceptive information is obtained by Golgi tendon organs and muscle spindles. * Golgi tendon organs consist of a fibrous capsule enclosing tendon fascicles and bare nerve endings that respond to tension in the tendon by causing action potentials in type Ib afferents. These fibers are relatively large, myelinated, and quickly conducting. * Muscle spindles monitor the length within muscles and send information via faster Ia afferents. These axons are larger and faster than type Ib (from both

nuclear bag fibers A nuclear bag fiber is a type of intrafusal muscle fiber that lies in the center of a muscle spindle. Each has many nuclei concentrated in bags and they cause excitation of the primary sensory fibers. There are two kinds of bag fibers based up ...

and

nuclear chain fiber A nuclear chain fiber is a specialized sensory organ contained within a muscle. Nuclear chain fibers are intrafusal fibers that, along with nuclear bag fibers, make up the muscle spindle responsible for the detection of changes in muscle length ...

s) and type II afferents (solely from nuclear chain fibers). All of these neurons are sensory (first order, or primary) and have their cell bodies in the

dorsal root ganglia A dorsal root ganglion (or spinal ganglion; also known as a posterior root ganglion) is a cluster of neurons (a ganglion) in a dorsal root of a spinal nerve. The cell bodies of sensory neurons known as first-order neurons are located in the do ...

. They pass through Rexed laminae layers I-VI of the

posterior grey column The posterior grey column (posterior cornu, dorsal horn, spinal dorsal horn, posterior horn, sensory horn) of the spinal cord is one of the three grey columns of the spinal cord. It receives several types of sensory information from the body, incl ...

(dorsal horn) to form synapses with second order or secondary neurons in layer VII just beneath the dorsal horn.

Tracts

The main spinocerebellar tracts are the dorsal and the ventral spinocerebellar tracts.

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

. 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

(first order neurons). These central processes travel through the

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 lateral funiculus ipsilaterally. The fibers continue to course through the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

of the

brainstem The brainstem (or brain stem) 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 cont ...

, at which point they pass through the inferior cerebellar peduncle and into the

, 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 A psychiatrist is a physician who specializes in psychiatry, the branch of medicine devoted to the diagnosis, prevention, study, and treatment of mental disorders. Psychiatrists are physicians and evaluate patients to determine whether their sy ...

and

neuropathologist Neuropathology is the study of disease of nervous system tissue, usually in the form of either small surgical biopsies or whole-body autopsies. Neuropathologists usually work in a department of anatomic pathology, but work closely with the clinic ...

Paul Flechsig Paul Emil Flechsig (29 June 1847, Zwickau, Kingdom of Saxony – 22 July 1929, Leipzig) was a German neuroanatomist, psychiatrist and neuropathologist. He is mainly remembered today for his research of myelinogenesis. Biography Born in Zwickau, h ...

Ventral spinocerebellar tract

The ventral spinocerebellar tract (or anterior spinocerebellar tract) conveys proprioceptive information from the body to the

. Historically, it has also been known as Gowers' column (or fasciculus or tract), after

Sir William Richard Gowers Sir William Richard Gowers (; 20 March 1845 – 4 May 1915) was a British neurologist, described by Macdonald Critchley in 1949 as "probably the greatest clinical neurologist of all time". He practised at the National Hospital for the Paraly ...

. 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 The anterior white commissure (ventral white commissure) is a bundle of nerve fibers which cross the midline of the spinal cord just anterior (in front of) to the gray commissure (Rexed lamina X). A delta fibers (Aδ fibers) and C fibers carryin ...

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 Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' (), ). In Latin anatomical terms, the form is used, e.g. . Similarly, the anatomical term chiasma is named aft ...

, 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 fibers of the ventral spinocerebellar tract then enters the cerebellum via the

superior cerebellar peduncle In the human brain, the superior cerebellar peduncle (brachium conjunctivum) is a paired structure of white matter that connects the cerebellum to the midbrain. It consists mainly of efferent fibers, the cerebellothalamic tract that runs from a cer ...

. 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). 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.

Comparison with dorsal spinocerebellar tract

When the dorsal roots are cut in a cat performing a step cycle, peripheral excitation is lost, and the dorsal spinocerebellar tract has no activity; the ventral spinocerebellar tract continues to show activity. This suggests that the dorsal spinocerebellar tract carries sensory information to the spinocerebellum through the inferior cerebellar peduncle during movement (since the inferior peduncle is known to contain fibres from the dorsal tract), and that the ventral spinocerebellar tract carries internally generated motor information about the movement through the superior cerebellar peduncle.

Posterior external arcuate fibers

The posterior external arcuate fibers (dorsal external arcuate fibers or cuneocerebellar tract) take origin in the accessory cuneate nucleus, and pass to the inferior cerebellar peduncle of the same side. The term "cuneocerebellar tract" is also used to describe exteroceptive and proprioceptive components that take origin in the

gracile Gracility is slenderness, the condition of being gracile, which means slender. It derives from the Latin adjective ''gracilis'' (masculine or feminine), or ''gracile'' ( neuter), which in either form means slender, and when transferred for examp ...

and cuneate nuclei; they pass to the inferior cerebellar peduncle of the same side. The posterior external arcuate fibers carry 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.) It is uncertain whether fibers are continued directly from the gracile and cuneate fasciculi into the inferior peduncle.

Rostral spinocerebellar tract

The rostral spinocerebellar tract is a tract which transmits information from the golgi tendon organs of the cranial half of the body to the

. It terminates bilaterally in the anterior lobe of the cerebellum (lower cerebellar peduncle) after travelling ipsilaterally from its origin in the cervical portion of the spinal cord. It reaches the cerebellum partly through the brachium conjunctivum (

) and partly through the restiform body ( inferior cerebellar peduncle).

Pathway for dorsal and spinocuneocerebellar tracts

The sensory neurons synapse in the

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 main ...

also known as ''Clarke's nucleus''. This is a column of relay neuron cell bodies within the medial gray matter within the spinal cord in layer VII (just beneath the dorsal horn), specifically between T1-L3. These neurons then send axons up the spinal cord, and project ipsilaterally to medial zones of the cerebellum through the inferior cerebellar peduncle. Below L3, relevant neurons pass into the

gracile fasciculus Gracility is slenderness, the condition of being gracile, which means slender. It derives from the Latin adjective ''gracilis'' (masculine or feminine), or ''gracile'' ( neuter), which in either form means slender, and when transferred for examp ...

(usually associated with the dorsal column–medial lemniscus pathway) until L3 where they synapse with the

(leading to considerable caudal enlargement). The neurons in the accessory cuneate nucleus have axons leading to the ipsilateral cerebellum via the inferior cerebellar peduncle.

Pathway for ventral and rostral spinocerebellar tracts

Some neurons of the ventral spinocerebellar tract instead form synapses with neurons in layer VII of L4-S3. Most of these fibers cross over to the contralateral lateral funiculus via the

and through the

. The fibers then often cross over again within the cerebellum to end on the ipsilateral side. For this reason the tract is sometimes termed the "double-crosser." The Rostral Tract synapses at the dorsal horn lamina (intermediate gray zone) of the spinal cord and ascends ipsilaterally to the cerebellum through the inferior cerebellar peduncle

Additional images

File:Gray680.png, Decussation of pyramids. File:Gray682.png, Superficial dissection of brain-stem. Lateral view. File:Gray684.png, Deep dissection of brain-stem. Lateral view. File:Gray683.png, Dissection of brain-stem. Lateral view. File:Gray691.png, Dissection of brain-stem. Dorsal view.

References

External links

* * * - dorsal external arcuate fibers * - cuneocerebellar tract
Anatomyatlases Plate17327

NIF Search - Anterior Spinocerebellar Tract
via the Neuroscience Information Framework {{Authority control Cerebellar connections Spinal cord tracts