Interposed nucleus

The interposed nucleus is the combined globose and emboliform nuclei on either side. The interposed nucleus is one of the paired cerebellar nuclei. It is located in the roof (dorsal aspect) of the fourth ventricle, lateral to the fastigial nucleus. The emboliform nucleus is the anterior interposed nucleus, and the globose nucleus is the posterior interposed nucleus.

The interposed nucleus is responsible for coordinating agonist/antagonist muscle pairs, and therefore a lesion in this area causes tremor.

Anatomy
The interposed nucleus is located in the paravermis of the cerebellum.

The interposed nucleus is smaller than the dentate but larger than the fastigial nucleus.

Afferents
The interposed nuclei receives Purkine cell terminal afferents from the paravermal cortex of the spinocerebellum, as well as collaterals of cerebellar afferents from the restiform body and anterior spinocerebellar tract.

It receives input from the ipsilateral posterior external arcuate fibers (cuneocerebellar tract) and the dorsal spinocerebellar tract, which originate in the accessory cuneate nucleus and the posterior thoracic nucleus, respectively.

Efferents
Afferents from the interposed nuclei leave the cerebellum through the brachium conjunctivum of the superior cerebellar peduncle. They project to:


 * contralateral (magnocellular division of) the red nucleus (→ rubrospinal tract). The red nucleus is the main target of tne interposed nuclei.
 * ipsilateral ventral lateral nucleus of thalamus (→ premotor cortex and primary motor cortex → lateral corticospinal tract).

The rubrospinal and lateral corticospinal tracts are subsequently involved in control of the distal musculature of the extremities.

Function
Functionally, it modulates muscle stretch reflexes of proximal limb muscles. The cerebellar interpositus nucleus is also required in delayed Pavlovian conditioning.