*4.3.2 Dorsal spinocerebellar tract (DSCT; posterior spinocerebellar tract, Flechsig's fasciculus, Foville-Flechsig fasciculus)*

This nucleus is present from Th1 through the second lumbar spinal segments and is largest in the lower thoracic and upper lumbar segments [77]. The cells of origin of the DSCT are classically described as residing in Clarke's column of the lumbar and thoracic spinal cord segments. The *nucleus dorsalis* of Clarke is a group of neurons localized in the medial part of lamina VII extending from C7 to L2 levels related to the proprioception of the lower limb. Caudally it begins at L2 level and reaches its maximum at Th12 level and above Th8 level its size diminishes, and the column ends at C7 level. Nevertheless, it is represented in other spinal regions by scattered neurons, which become aggregated to form a cervical nucleus at C3 level and a sacral nucleus in the middle of the sacral spine region (**Figure 2**).

**9**

*Structural and Biological Basis for Proprioception DOI: http://dx.doi.org/10.5772/intechopen.96787*

*4.3.3 Rostral spinocerebellar tract*

*arcuate fibers)*

the spinocerebellum.

*4.3.5 Other spinocerebellar tracts*

*lar* tract and the direct *spinoolivocerebellar* tract.

lum to coordinate and regulate motor activity.

**4.4 The brain connection – conscious proprioception**

In addition, other groups of neurons that also belong to DSCT are located throughout the intermediate and dorsal laminae of the thoracic and lumbosacral segments of the spinal cord. The axons of the DSCT ascends ipsilaterally in the peripheral region of the funiculus lateralis of the spinal cord. Then, they continue to course through the medulla oblongata and finally pass through the inferior cerebellar peduncle and into the cerebellum, and terminate in the cerebellar cortex of lobules I–V, in the anterior lobe and in the posterior lobe vermis and paramedian lobe. In addition to those cortical projections, there is evidence that DSCT fibers

The rostral spinocerebellar tract appears to be the upper extremity homolog of the ventral spinocerebellar tract. The neurons of origin of this tract are located in Rexed laminae V-VII of the C5-C8 segments. The projection is predominantly ipsilateral, but there is also a minor bilateral projection. The axons of the rostral spinocerebellar tract neurons terminate in the anterior and paramedian lobule cerebellar.

DSCT does not convey information from the upper limb since the *nucleus dorsalis* does not extend into the cervical spinal cord. Therefore, there is another proprioceptive pathway for the upper limb: the cuneocerebellar tract. The secondary order neurons of this nucleus pass to the inferior ipsilateral cerebellar peduncle to reach

There are additional ascending direct and indirect spinocerebellar pathways. The *spinocervical tract* relays in the lateral cervical nucleus and projects to the ventral postero-lateral (VPL) nucleus of the thalamus. The *spinohypothalamic* and *spinoamygdalar* tract provides sensory input to areas of the nervous system involved in controlling autonomic, endocrine and emotional responses. Sensory information from the hindlimbs is also relayed by indirect *spinoreticulocerebellar* pathways through at least two olivocerebellar pathways: the indirect *spinoreticuloolivocerebel-*

These pathways provide necessary information regarding the current status of reflex pathways, as well as muscle tone, length and tension that consent the cerebel-

According to Proske and Gadivia [4] there are at least two reasons for including body schemas and images in the study and discussion of proprioception. "*First, while proprioceptors provide information about position and movement of the limb, they are unable to signal the length of limb segments and therefore the absolute location of the limb in space. Second, there is the issue of body ownership*". The blind movement of a limb, while proprioceptive feedback informs us about the movement, we need to be able to identify the moving limb as our own [78, 79]. Carruthers has proposed that all representations of the body are available to consciousness [80]. "On-line," newly constructed body representations, provided by inputs from vision, touch, and

*4.3.4 Cuneocerebellar tract (posterior external arcuate fibers, dorsal external* 

also terminate in the medial and interpositus cerebellar nuclei.

*Structural and Biological Basis for Proprioception DOI: http://dx.doi.org/10.5772/intechopen.96787*

*Proprioception*

ate nucleus.

*fascicle)*

**lateral Bechterew's columns**

localized at these places form the spinocerebellar tracts.

give collaterals to the globose and emboliform nuclei.

*fasciculus, Foville-Flechsig fasciculus)*

**4.3 The spinocerebellar tracts – unconscious proprioception**

individual pathways: ventral, dorsal, rostral and cuneocerebellar.

*4.3.1 Ventral spinocerebellar tract (VSCT; anterior spinocerebellar, Gowers'* 

The peripheral branch of the axons of the proprioceptive pseudo-unipolar neurons forms large-myelinated Aα and Aβ fibers in peripheral nerves, while the central branch stablish synapse in the spinal cord or ascends throughout the dorsal columns of the spinal cord to reach the gracile and cuneate nuclei in the medulla. Some peripheral branches, however, travel through the cuneatus tract and ascend the cervical spinal cord to reach the medulla oblongata to reach the accessory cune-

**4.2 Secondary order neurons: the medial stilling-Clarke's (***nucleus dorsalis***) and** 

The secondary order neurons of the proprioceptive pathways are localized at the base of the dorsal horn of the spinal cord, in correspondence with the VII Rexed's lamina, also known as the intermediate zone of the spinal cord. In this place two nuclear columns were classically considered: the nucleus dorsalis of Clarke (also known as Clarke's column, dorsal nucleus, posterior thoracic nucleus) and the medial nucleus (also known as Bechterew's nucleus). The axons of the neurons

The tracts that carry unconscious proprioceptive information are collectively known as the spinocerebellar tracts. Within the spinocerebellar tracts, there are four

VSCT originates mainly from the medial part of lamina 7 in the lumbosacral segments, from the dorsolateral nucleus of lamina 9 at L3-L6, and also from the neurons of the ventrolateral nucleus of lamina 9 and the lateral part of lamina 7 at L4-L5 segments [76, 77]. Axons decussate in the anterior white commissure and run in the ventral border of the lateral funiculi. They ascend through the brainstem to the pons where turn dorsally and enter the cerebellum throughout the superior cerebellar peduncle. For the most part, the ventral spinocerebellar tract axons recross the midline in the deep white matter of the cerebellum to terminate ipsilaterally. It terminates in the cortex of the anterior lobe and vermis of the posterior lobe and

*4.3.2 Dorsal spinocerebellar tract (DSCT; posterior spinocerebellar tract, Flechsig's* 

and a sacral nucleus in the middle of the sacral spine region (**Figure 2**).

This nucleus is present from Th1 through the second lumbar spinal segments and is largest in the lower thoracic and upper lumbar segments [77]. The cells of origin of the DSCT are classically described as residing in Clarke's column of the lumbar and thoracic spinal cord segments. The *nucleus dorsalis* of Clarke is a group of neurons localized in the medial part of lamina VII extending from C7 to L2 levels related to the proprioception of the lower limb. Caudally it begins at L2 level and reaches its maximum at Th12 level and above Th8 level its size diminishes, and the column ends at C7 level. Nevertheless, it is represented in other spinal regions by scattered neurons, which become aggregated to form a cervical nucleus at C3 level

**8**

In addition, other groups of neurons that also belong to DSCT are located throughout the intermediate and dorsal laminae of the thoracic and lumbosacral segments of the spinal cord. The axons of the DSCT ascends ipsilaterally in the peripheral region of the funiculus lateralis of the spinal cord. Then, they continue to course through the medulla oblongata and finally pass through the inferior cerebellar peduncle and into the cerebellum, and terminate in the cerebellar cortex of lobules I–V, in the anterior lobe and in the posterior lobe vermis and paramedian lobe. In addition to those cortical projections, there is evidence that DSCT fibers also terminate in the medial and interpositus cerebellar nuclei.

## *4.3.3 Rostral spinocerebellar tract*

The rostral spinocerebellar tract appears to be the upper extremity homolog of the ventral spinocerebellar tract. The neurons of origin of this tract are located in Rexed laminae V-VII of the C5-C8 segments. The projection is predominantly ipsilateral, but there is also a minor bilateral projection. The axons of the rostral spinocerebellar tract neurons terminate in the anterior and paramedian lobule cerebellar.
