Internal arcuate fibers

Axons of neurons that compose the brain's gracile and cuneate nuclei

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. Arcuate nucleus (medulla). 14. Vagus. 15. Hypoglossal.

Section of the medulla oblongata at about the middle of the olive. (Arcuate fibers labeled at center right.)

Details
Identifiers
Latin| fibrae arcuatae internae
NeuroNames| 795
NeuroLex ID| birnlex_1091
TA98| A14.1.04.109
TA2| 6042
FMA| 72629
Anatomical terms of neuroanatomy

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In neuroanatomy, the internal arcuate fibers or internal arcuate tract are the axons of second-order sensory neurons that compose the gracile and cuneate nuclei of the medulla oblongata. These second-order neurons begin in the gracile and cuneate nuclei in the medulla. They receive input from first-order sensory neurons, which provide sensation to many areas of the body and have cell bodies in the dorsal root ganglia of the dorsal root of the spinal nerves. Upon decussation (crossing over) from one side of the medulla to the other, also known as the sensory decussation, they are then called the medial lemniscus.

The internal arcuate fibers are part of the second-order neurons of the posterior column-medial lemniscus system, and are important for relaying the sensation of fine touch and proprioception to the thalamus and ultimately to the cerebral cortex.

## External links

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* Hier-792 at NeuroNames
* Photo at Indiana.edu

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Anatomy of the medulla

Grey matter|

| Cranial nuclei|

| afferent:|

* Solitary nucleus
* tract
* Dorsal respiratory group
* Gustatory nucleus
* Vestibular nuclei
* Lateral
* Medial
* Inferior

|

efferent:|

* Hypoglossal nucleus
* Nucleus ambiguus
* Dorsal nucleus of vagus nerve
* Inferior salivatory nucleus

Dorsal|

* Gracile nucleus
* Cuneate nucleus
* Accessory cuneate nucleus

Ventral|

*     * Ventral respiratory group
* Arcuate nucleus of medulla
* Rostral ventromedial medulla
* Botzinger complex
* Pre-Bötzinger complex

White matter|

| Dorsal|

* Sensory
* Sensory decussation
* Medial lemniscus
* Juxtarestiform body
* Ascending dorsal longitudinal fasciculus
* Medial longitudinal fasciculus
* Motor
* Descending dorsal longitudinal fasciculus
* Medial longitudinal fasciculus

|

Ventral|

* Descending tracts
* Olivocerebellar tract
* Rubro-olivary tract

Surface|

| Front|

* Pyramid
* Anterior median fissure
* Anterolateral sulcus
* Olive
* Inferior olivary nucleus

|

Back|

* Posterior median sulcus
* Posterolateral sulcus
* Area postrema
* Vagal trigone
* Hypoglossal trigone
* Medial eminence
* Inferior cerebellar peduncle

Grey|

* Reticular formation
* Gigantocellular
* Parvocellular
* Ventral
* Lateral
* Paramedian
* Raphe nuclei
* Obscurus
* Magnus
* Pallidus
* Perihypoglossal nuclei

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Brain and spinal cord: neural tracts and fasciculi

Sensory|

| DCML|

| 1°:|

* Pacinian corpuscle/Meissner's corpuscle → Posterior column (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° (Spinomesencephalic 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|

| 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 nuclei → 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 nuclei

Bidirectional:
Spinocerebellar|

| Unconscious
proprioception|

* 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)

Authority control databases |

* Terminologia Anatomica

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