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Located in the medulla oblongata, the gracile nucleus is one of the dorsal column nuclei that participates in the sensation of fine touch and proprioception. It contains second-order neurons of the dorsal column-medial lemniscus system 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 primary sensory trigeminal nucleus).
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.
|Brain: rhombencephalon (hindbrain)|
surface: Locus ceruleus
Trigeminal lemniscus (Dorsal trigeminal tract, Ventral trigeminal tract)
cranial nuclei: GSA: Principal V/Spinal V - VIII-c (Dorsal, Anterior)/VIII-v (Lateral, Superior, Medial, Inferior) - SVE: Motor V - VII - GSE: VI - GVE: VII: Superior salivary nucleus
MLF, III, IV and VI (vestibulo-oculomotor fibers, medial vestibulospinal tract)
sensory/ascending: Trapezoid body/VIII - Superior olivary nucleus
Inferior cerebellar peduncle (Vestibulocerebellar tract)
motor/descending: Apneustic center • Pneumotaxic center (Medial parabrachial nucleus) - Lateral parabrachial nucleus
Middle cerebellar peduncles (Pontocerebellar fibers) - Pontine nuclei
motor/descending: Corticospinal tract - Corticobulbar tract - Corticopontine fibers
Reticular formation (Caudal, Oral, Tegmental, Paramedian) • Raphe nuclei (Median)
surface: Posterior median sulcus - Postero-lateral sulcus - Area postrema
cranial nuclei: GVA: VII,IX,X: Solitary/tract • SVA: Gustatory nucleus • GSE: XII • GVE: IX,X,XI: Ambiguus • SVE: X: Dorsal • IX: Inferior salivatory nucleus - MLF, III, IV and VI
sensory/ascending: Gracile nucleus • Cuneate nucleus (Accessory cuneate nucleus) • Sensory decussation • Medial lemniscus
motor/descending: Dorsal respiratory group
motor/descending: Ventral respiratory group - Pyramid (Motor decussation) - Inferior olivary nucleus (Olivocerebellar tract, Rubro-olivary tract)
surface: Anterior median fissure - Antero-lateral sulcus - Arcuate nucleus of medulla - Olivary body
Reticular formation (Gigantocellular, Parvocellular, Ventral, Lateral, Paramedian) • Raphe nuclei (Obscurus, Magnus, Pallidus)