SPINOCEREBELLUM

SPINOCEREBELLUM

(PALEOCEREBELLUM)

Spinoerebellum is connected with spinal cord and hence the name. It forms the major receiving area of cerebellum for sensory inputs. It is concerned with the maintenance of muscle tone and anticipatory adjustment of muscle contraction during movement. Spinocerebellum is also phylogenetically older part of cerebellum. It is otherwise called paleocerebellum.

COMPONENTS

Spinocerebellum consists of medial portions of cerebellar hemisphere, paraflocculi and the parts of vermis, viz. lingula, central lobe, culmen, lobules simplex, declive, tuber, pyramid and uvula. However, some physiologists do not consider uvula as a part of spinocerebellum.

CONNECTIONS

Afferent Connections

1. Dorsal spinocerebellar tract

Dorsal spinocerebellar tract arises from Clarke’s column of cells in the dorsal gray horn of spinal cord. It is uncrossed tract and reaches the spinocerebellum through the inferior peduncle of same side. This tract conveys the proprioceptive information from the limbs of same side regarding the position and

movements.

2. Ventral spinocerebellar tract

Fibers of ventral spinocerebellar tract arise from the marginal cells in the dorsal gray horn of spinal cord. After taking the origin, the fibers cross the midline, ascend in the opposite side and reach the spinocerebellum through superior cerebellar peduncle. This tract conveys the information about the position and movements ofopposite limbs to spinocerebellum.

3. Cuneocerebellar tract

Cuneocerebellar tract arises from accessory cuneate nucleus, situated lateral to cuneate nucleus in

medulla. It reaches the spinocerebellum through the inferior cerebellar peduncle of the same side. This

tract conveys the proprioceptive impulses from upper limb, upper trunk and neck to spinocerebellum.

4. Olivocerebellar tract

Olivocerebellar tract is formed by climbing fibers arising from the inferior olivary nucleus in medulla. After

taking origin, these fibers cross the midline and reach the spinocerebellum through the inferior cerebellar

peduncle of the opposite side. This tract also gives collaterals to cerebellar nuclei, particularly the globosus nucleus and emboliform nucleus. Inferior olivary nucleus receives afferent fibers from three sources:

i. Brainstem nuclei of same side

ii. Spinal cord through spino-olivary tract of same side

iii. Cerebral cortex of opposite side.

Olivocerebellar tract conveys proprioceptive impulses from the body and output signals from

cerebral cortex to spinocerebellum.

5. Pontocerebellar tract

Pontocerebellar tract arises from pontine nuclei, crosses the midline and reaches the spinocerebellum

through the middle cerebellar peduncle of opposite side. Pontine nuclei receive afferents from cerebral

cortex. Pontocerebellar tract conveys the information to spinocerebellum about the motor signals discharged from cerebral cortex.

6. Tectocerebellar tract

Tectocerebellar tract arises from superior and inferior colliculi of tectum in midbrain. It reaches the

spinocerebellum through superior cerebellar peduncle of the same side. This tract carries visual impulses from superior colliculus and auditory impulses from inferior colliculus to spinocerebellum.

7. Trigeminocerebellar tract

Trigeminocerebellar tract is formed by the fibers arising from mesencephalic nucleus of trigeminal

nerve. It reaches the spinocerebellum via superior cerebellar peduncle of same side. This tract conveys

proprioceptive information from jaw muscles and temporomandibular joint to spinocerebellum. It also

carries the sensory impulses from the periodontal tissues (tissues around the teeth) to spinocerebellum.

Efferent Connections

Cortex of spinocerebellum is projected into the nuclei fastigi, emboliformis and globosus of cerebellum. Fibers

from these nuclei pass through following tracts:

1. Fastigiobulbar tract

Fastigiobulbar tract arises from fastigial nucleus, passes through superior cerebellar peduncle of same

side and ends in the reticular formation.

2. Cerebelloreticular tract

Fibers of cerebelloreticular tract arise from the emboliform and globosus nuclei, pass through superior

cerebellar peduncle of same side and terminate in the reticular formation.

From reticular formation, reticulospinal tract arise and terminate on the gamma motor neurons of spinal cord.

3. Cerebello-olivary tract

Cerebello-olivary tract arises from the emboliform and globosus nuclei and reaches the inferior olivary

nucleus of the same side by passing through the superior cerebellar peduncle. From olivary nucleus, the

olivospinal tract arises and fibers of this tract end on the alpha motor neurons of spinal cord.

FUNCTIONS

Spinocerebellum regulates tone, posture and equilibrium by receiving sensory impulses form tactile receptors, proprioceptors, visual receptors and auditory receptors. Spinocerebellum is the receiving area for tactile, proprioceptive, auditory and visual impulses. It also receives the cortical impulses via pontine nuclei. Tactile and proprioceptive impulses are localized in the spinocerebellum. Localization of tactile and proprioceptive impulses in spinocerebellum is determined by stimulating the tactile receptors and

the proprioceptors and by recording the electrical responses in different parts of spinocerebellum. The

different parts of the body are represented in the spinocerebellum in the following manner:

Lingula : Coccygeal region

Central lobe : Hind limb

Culmen : Forelimb

Lobulus simplex : Face and head.

In cerebral cortex, different parts of the body are represented in an inverted manner. But in cerebellum,

different parts are represented in upright manner. Spinocerebellum regulates the postural reflexes by

modifying muscle tone. It facilitates the discharge from gamma motor neurons in spinal cord via cerebellovestibulospinal and cerebello-reticulospinal fibers. Increased discharge from gamma motor neurons increases the muscle tone. Lesion, destruction or abolishing the function of spinocerebellum by cooling, causes stoppage of discharge from gamma motor neurons, resulting in hypotonia and disturbances in posture. Spinocerebellum also receives impulses from optic and auditory pathway and helps in adjustment of posture and equilibrium in response to visual and auditory impulses.

 

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