Human Anatomy - Kotsan I. Y. 2009

Pathways of the Brain and Spinal Cord
Descending Pathways from the Cerebrum to the Cerebellum

The Cerebral Cortex, which governs all body processes, also exerts a controlling and regulatory influence on cerebellar activity. This is achieved through the corticopontocerebellar pathway (tractus corticopontocerebellaris), which extends from the cerebral cortex to the cerebellar cortex. This pathway is disynaptic (two-neuron) and features a decussation in the Pons.

The Cell bodies of the first-order Neurons are located in the cerebral cortex (layer V). Their axons terminate on the Cells of the pontine nuclei on the same side, forming the corticopontine tract. Depending on the specific lobe of the cerebral cortex where the cell bodies of the first-order neurons originate, this pathway is divided into 4 tracts:

1. Frontopontine tract — the cell bodies of the first-order neurons are situated in the frontal cortex. Their axons participate in The formation of the corona radiata of the cerebral hemispheres and then converge into a bundle that passes through the posterior part of the anterior limb of the internal capsule. From there, the fibers of the frontopontine tract travel through the medial portion of the cerebral peduncle base and terminate on the neurons of the pontine nuclei.

2. Parietopontine tract — the cell bodies of the first-order neurons are located in the parietal cortex.

3. Temporopontine tract — the cell bodies of the first-order neurons are situated in the temporal cortex.

4. Occipitopontine tract — the cell bodies of the first-order neurons are located in the occipital cortex.

As the nerve fibers of the temporopontine and occipitopontine tracts course deep into the cerebral hemisphere, they converge into a compact bundle that passes through the middle portion of the posterior limb of the internal capsule. Subsequently, via the lateral part of the cerebral peduncle base, the fibers extend to the pontine nuclei.

The axons of the second-order neurons (the neurons of the pontine nuclei) cross to the opposite side and form the pontocerebellar tract. The fibers of this pathway constitute the middle cerebellar peduncles, through which they reach the cortex of the cerebellar hemispheres.

Thus, the projection PATHWAYS OF THE Brain AND SPINAL cord establish connections between afferent and efferent (effector) centers, completing complex reflex arcs within The Human Body. Some of these arcs are integrated at phylogenetically older nuclei located in the Brainstem, which mediate automatic Functions independently of conscious control, albeit under the Supervision of the cerebral hemispheres; others are integrated with the involvement of the cerebral cortex (the higher centers of the Central Nervous system) and mediate conscious actions of Organs and Organ Systems. Functionally, these pathways unify the Organism into a single, cohesive entity and ensure the coordination of its activities.

Key Latin Terms

Arcuate fibers of cerebrum — fibrae arcuatae cerebri

Cingulum — cingulum

Superior longitudinal fasciculus — fasciculus longitudinalis superior

Inferior longitudinal fasciculus — fasciculus longitudinalis inferior

Uncinate fasciculus — fasciculus uncinatus

Fronto-occipital fasciculus — fasciculus frontooccipitale

Anterior, lateral, and posterior own fasciculi — fasciculi proprii

anteriores, laterales et posteriores

Corpus callosum — corpus callosum

Radiation of corpus callosum — radiatio corporis callosi

Forceps frontalis (minor) — forceps (minor) frontalis

Forceps occipitalis (major) — forceps (major) occipitalis

Anterior commissure — comissura anterior

Epithalamic (posterior) commissure — comissura epithalamica (posterior)

Commissure of fornix — comissura fornicis

Lateral spinothalamic tract — tractus spinothalamicus lateralis

Anterior spinothalamic tract — tractus spinothalamicus anterior

Ganglio-bulbo-thalamocortical tract — tractus ganglio-bulbo-thalamocorticalis

Anterior spinocerebellar tract — tractus spinocerebellaris anterior

Posterior spinocerebellar tract — tractus spinocerebellaris posterior

Corticospinal (pyramidal) tract — tractus

corticospinalis (pyramidalis)

Corticonuclear tract — tractus corticonuclearis

Rubrospinal tract — tractus rubrospinalis

Vestibulospinal tract — tractus vestibulospinalis

Tectospinalis tract — tractus tectospinalis

Reticulospinal tract — tractus reticulospinalis

Olivospinal tract — tractus olivospinalis

Cerebellorubrospinal tract — tractus cerebe-llorubrospinalis

Corticopontocerebellar tract — tractus corticopontocerebellaris