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Internal arcuate fibers

Diagram showing the course of the arcuate fibers. (Testut.) 1. Medulla oblongata anterior surface. 2. Anterior median fissure. 3. Fourth ventricle. 4. Inferior olivary nucleus, with the accessory olivary nuclei. 5. Gracile nucleus. 6. Cuneate nucleus. 7. Trigeminal. 8. Inferior peduncles, seen from in front. 9. Posterior external arcuate fibers. 10. Anterior external arcuate fibers. 11. Internal arcuate fibers. 12. Peduncle of inferior olivary nucleus. 13. Nucleus arcuatus. 14. Vagus. 15. Hypoglossal.

Section of the medulla oblongata at about the middle of the olive. (Arcuate fibers labeled at center right.)
Latin	fibrae arcuatae internae
Gray's	subject #187 782

Internal arcuate fibers are the axons of second-order neurons contained within the gracile and cuneate nuclei of the medulla oblongata.

These fibers cross (decussate) from one side of the medulla to the other to form the medial lemniscus.

Part of the dorsal column-medial lemniscus system (second neuron), the internal arcuate fibers are important for relaying the sensation of fine touch and proprioception to the thalamus and ultimately to the cerebral cortex.

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Dorsal

Surface	Posterior median sulcus · Posterolateral sulcus · Area postrema · Vagal trigone · Hypoglossal trigone · Medial eminence

Grey: Cranial nuclei	afferent: GVA: VII,IX,X: Solitary/tract/Dorsal respiratory group · SVA: Gustatory nucleus · GSA: VIII-v (Lateral, Medial, Inferior) efferent: GSE: XII · GVE: IX,X,XI: Ambiguus · SVE: X: Dorsal · IX: Inferior salivatory nucleus

Grey: other	Gracile nucleus · Cuneate nucleus (Accessory cuneate nucleus)

White: Sensory/ascending	Sensory decussation · Medial lemniscus · Inferior cerebellar peduncle (Juxtarestiform body) · Ascending dorsal longitudinal fasciculus · MLF, III, IV and VI

White: Motor/descending	Descending dorsal longitudinal fasciculus · MLF, III, IV and VI

Ventral

White: Motor/descending	Motor decussation · Olivocerebellar tract · Rubro-olivary tract

Grey matter	Ventral respiratory group · Arcuate nucleus of medulla · Inferior olivary nucleus

Surface	Anterior median fissure · Antero-lateral sulcus · Olive · Pyramid

Grey: Raphe/
reticular

Sensory/
ascending

Fast/lateral	1° (Free nerve ending → A delta fiber) → 2° (Anterior white commissure → Lateral and Anterior Spinothalamic tract → Spinal lemniscus → VPL of Thalamus) → 3° (Postcentral gyrus) → 4° (Posterior parietal cortex) 2° (Spinotectal tract → Superior colliculus of Midbrain tectum)

Slow/medial	1° (Group C nerve fiber → Spinoreticular tract → Reticular formation) → 2° (MD of Thalamus) → 3° (Cingulate cortex)

Motor/
descending

Pyramidal	flexion: Primary motor cortex → Posterior limb of internal capsule → Decussation of pyramids → Corticospinal tract (Lateral, Anterior) → Neuromuscular junction

Extrapyramidal	flexion: Primary motor cortex → Genu of internal capsule → Corticobulbar tract → Facial motor nucleus → Facial muscles flexion: Red nucleus → Rubrospinal tract extension: Vestibulocerebellum → Vestibular nuclei → Vestibulospinal tract extension: Vestibulocerebellum → Reticular formation → Reticulospinal tract Midbrain tectum → Tectospinal tract → muscles of neck

Basal ganglia	direct: 1° (Motor cortex → Striatum) → 2° (GPi) → 3° (Lenticular fasciculus/Ansa lenticularis → Thalamic fasciculus → VL of Thalamus) → 4° (Thalamocortical radiations → Supplementary motor area) → 5° (Motor cortex) indirect: 1° (Motor cortex → Striatum) → 2° (GPe) → 3° (Subthalamic fasciculus → Subthalamic nucleus) → 4° (Subthalamic fasciculus → GPi) → 5° (Lenticular fasciculus/Ansa lenticularis → Thalamic fasciculus → VL of Thalamus) → 6° (Thalamocortical radiations → Supplementary motor area) → 7° (Motor cortex) nigrostriatal pathway: Pars compacta → Striatum

Afferent	Vestibular nucleus → Vestibulocerebellar tract → ICP → Cerebellum → Granule cell Pontine nuclei → Pontocerebellar fibers → MCP → Deep cerebellar nuclei → Granule cell Inferior olivary nucleus → Olivocerebellar tract → ICP → Hemisphere → Purkinje cell → Deep cerebellar nuclei

Efferent	Dentate nucleus in Lateral hemisphere/pontocerebellum → SCP → Dentatothalamic tract → Thalamus (VL) → Motor cortex Interposed nucleus in Intermediate hemisphere/spinocerebellum → SCP → Reticular formation, or → Cerebellothalamic tract → Red nucleus → Thalamus (VL) → Motor cortex Fastigial nucleus in Flocculonodular lobe/vestibulocerebellum → Vestibulocerebellar tract → Vestibular nucleus

Bidirectional: Spinocerebellar	Unconscious proprioception: Golgi tendon organ → ICP/SCP → Spinocerebellar (Dorsal/Posterior thoracic nucleus, Cuneocerebellar) → Cerebellum Reflex arc: Ventral - Rostral

see also white matter fibers

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