Gracile nucleus

Gracile nucleus
Section of the medulla oblongata at the level of the decussation of the pyramids. Gracile nucleus is #8.
Dissection of brain-stem. Dorsal view. ("nucleus gracilis" is labeled on left, second from the bottom.)
Details
Identifiers
Latin	nucleus gracilis
NeuroNames	hier-763
NeuroLex ID	Gracile nucleus
TA	A14.1.04.201
FMA	72602
*Anatomical terms of neuroanatomy* [edit on Wikidata]

Located in the medulla oblongata, the gracile nucleus is one of the dorsal column nuclei that participate in the sensation of fine touch and proprioception of the lower body (legs and trunk). It contains second-order neurons of the posterior column-medial lemniscus pathway, which receive inputs from sensory neurons of the dorsal root ganglia and send axons that synapse in the thalamus.

The neurons contained within the nucleus form a visible bump called the gracile tubercle on the posterior side of the closed medulla at the floor of the fourth ventricle.

The gracile nucleus and fasciculus carry epicritic, kinesthetic, and conscious proprioceptive information from the lower part of the body (below the level of T6 in the spinal cord). The counterpart to the gracile nucleus and fasciculus is the cuneate nucleus and fasciculus, which carries the same type of information, but from the upper body (above T6, excepting the face and ear - the information from the face and ear is carried by the principal sensory nucleus of trigeminal nerve).

Additional images

Decussation of pyramids.
Dissection of brain-stem. Lateral view.
Deep dissection of brain-stem. Lateral view.
Superior terminations of the posterior fasciculi of the medulla spinalis.
Section of the medulla oblongata at about the middle of the olive.
Diagram showing the course of the arcuate fibers.
The formatio reticularis of the medulla oblongata, shown by a transverse section passing through the middle of the olive.
Scheme showing the course of the fibers of the lemniscus; medial lemniscus in blue, lateral in red.
Transverse section passing through the sensory decussation.
Deep dissection of cortex and brain-stem.
The sensory tract.
Fourth ventricle. Posterioe view.Deep dissection.

External links

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

Ventral

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 decussation 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

Brain and spinal cord: neural tracts and fasciculi

Sensory/
ascending

PCML

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/
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 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)

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