Posterior external arcuate fibers

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Posterior external 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 externae posteriores
Gray's	subject #187 783

The posterior external arcuate fibers (dorsal external arcuate fibers) take origin in the gracile and cuneate nuclei; they pass to the inferior peduncle of the same side.

It is uncertain whether fibers are continued directly from the gracile and cuneate fasciculi into the inferior peduncle.

The term "cuneocerebellar tract" is sometimes used to collectively refer to the posterior external arcuate fibers.^[1]

The term "cuneocerebellar tract" is also used to describe an analogue to the dorsal spinocerebellar tract for the upper limbs.^[2] In this context, the "cuneo-" derives from the accessory cuneate nucleus, not the cuneate nucleus. (The two nuclei are related in space, but not in function.)

Contents

1 See also
2 References
3 Additional images
4 External links

References

^ Sabyasachi Sircar (2007). Principles of Medical Physiology. Stuttgart: Georg Thieme Verlag. pp. 608. ISBN 1-58890-572-1.
^ Fix, James D. (2002). Neuroanatomy. Hagerstwon, MD: Lippincott Williams & Wilkins. pp. 133. ISBN 0-7817-2829-0.

Additional images

Dissection of brain-stem. Lateral view.
Deep dissection of brain-stem. Lateral view.
Dissection of brain-stem. Dorsal view.

External links

NeuroNames hier-793 - dorsal external arcuate fibers
NeuroNames hier-800 - cuneocerebellar tract

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.

Human brain: rhombencephalon, myelencephalon: medulla (TA A14.1.04, GA 9.767)

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 · Rostral ventromedial medulla

Surface	Anterior median fissure · Anterolateral sulcus · Olive · Pyramid

Grey: Raphe/
reticular

Reticular formation (Gigantocellular, Parvocellular, Ventral, Lateral, Paramedian) · Raphe nuclei (Obscurus, Magnus, Pallidus)

M: CNS

anat(n/s/m/p/4/e/b/d/c/a/f/l/g)/phys/devp

noco(m/d/e/h/v/s)/cong/tumr, sysi/epon, injr

proc, drug(N1A/2AB/C/3/4/7A/B/C/D)

Brain and spinal cord: neural tracts and fasciculi

Sensory/
ascending

PCML

1°: Pacinian corpuscle/Meissner's corpuscle → Gracile fasciculus/Cuneate fasciculus → Gracile nucleus/Cuneate nucleus

2°: → sensory decussation/arcuate fibers (Posterior external arcuate fibers, Internal arcuate fibers) → Medial lemniscus/Trigeminal lemniscus → Thalamus (VPL, VPM)

3°: → Posterior limb of internal capsule → Postcentral gyrus

Anterolateral/
pain

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

Cerebellar

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

Unc. prop.	lower limb → 1° (muscle spindles → DRG) → 2° (Posterior thoracic nucleus → Dorsal/posterior spinocerebellar tract → ICP → Cerebellar vermis) upper limb → 1° (muscle spindles → DRG) → 2° (Accessory cuneate nucleus → Cuneocerebellar tract → ICP → Anterior lobe of cerebellum)

Reflex arc	lower limb → 1° (Golgi tendon organ) → 2° (Ventral/anterior spinocerebellar tract→ SCP → Cerebellar vermis) upper limb → 1° (Golgi tendon organ) → 2° (Rostral spinocerebellar tract → ICP → Cerebellum)

M: CNS

anat(n/s/m/p/4/e/b/d/c/a/f/l/g)/phys/devp

noco(m/d/e/h/v/s)/cong/tumr, sysi/epon, injr

proc, drug(N1A/2AB/C/3/4/7A/B/C/D)

M: PNS

anat(h/r/t/c/b/l/s/a)/phys(r)/devp/prot/nttr/nttm/ntrp

noco/auto/cong/tumr, sysi/epon, injr

proc, drug(N1B)

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