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Bús Flóra
EMK0EA
Organization rules of the brain stem: descending neuronal pathways
Brain stem has structurally 3 parts: Mesencephalon, Pons, Medulla oblongata.
First of all, important somatic and autonomic centers are located in there, and the processing centers of the
cranial nerves are also. Moreover, it’s a functionally significant system because the reticular formation
controlling vital respitatory and circulatory mechanism and arousal, is also part of the brain stem.
Furthermore, major motor and sensory projections pass through the brain stem.
I categorized the descending neuronal pathways into 3 groups:
1. Descending neural pathways originating from the brain stem
1. tractus tectospinalis: originates from the colliculus superior of the mesencephalon. Controls the
movement of the head.
2. tractus vestibulospinalis: it arises from the lateral vestibular nucleus (pons), it mediates cerebellar
and vestibular information toward the spinal cord. Exerts facilitatory influance on spinal reflexes
and controls muscle tone.
3. tractus rubrospinalis: originates from the red nucleus of the brain stem (mesencephalon) and
terminates on ventral horn interneurons. It conveys information from the cortex and cerebellum
mainly to motor neurons innervating flexor and extensor muscles.
4. tractus reticulospinalis: carries information from the reticular formation to the dorsal and ventral
horns. Controls voluntary movements, muscle tone, central sensory transmission. Regulates
respitatory and circulatory activities.
5. fasciulus longitudinalis medialis: originates from the caudal part part of the brain stem. Carries
information from secondary vestibular neurons to cervical segments. Controls the movement of
the head, commands for eye movement.
2. Descending neuronal pathways through the brain stem:
tractus corticospinalis: it has motor function: face muscles and voluntary movements
a. Tractus corticospinalis cruciatus: originates from the cerebral cortex, runs through the internal
capsule, crossed in the medulla oblongata and terminates on interneurons of the ventral horn
that are associated with motoneurons. The main regulatory tract of lower motoneurons.
b. tractus corticospinalis directus: crossing at level of target segment. Carries motor commands to
neurons. Originates from the cerebral cortex and terminates in the intermediate zone of the grey
matter.
3. Descending Neuronal pathways terminating in the brain stem:
1. tractus corticorubralis: originates from the cerebral cortex terminates in the red nucleus of the
mesencephalon
2. tractus corticopontinus: orignates from the cerebral cortex, descend in the internal capsule
and terminate in the nuclei pontis of the pons.
3. fasciulus tegmentalis centralis: originates from the thalamus or from the red nucleus and
terminates in the olivia inferior of the medulla oblongata.
4. tractus corticobulbaris,tractus corticomesencephalicus: The corticobulbar tract is one of the
pyramidal tracts, it’s carrying the motor function of the non-oculomotor cranial nerves.
5. fasiculus longitudinalis dorsalis: originates from the hypothalamus and terminates in the
reticular formation.