Cerebellum: Pathways & Midline Structures
Pathways & Midline Structures of Cerebellum
The middle cerebellar peduncle (MCP)
- Is an afferent pathway into the cerebellum.
- It encompasses fibers that originate from pontine nuclei.
The inferior cerebellar peduncle (ICP)
- Is an afferent pathway into the cerebellum.
- it receives fibers from throughout the brainstem and spinal cord.
The superior cerebellar peduncle (SCP)
- Sends efferent fibers out of the cerebellum.
Note the following major exceptions to the aforementioned rules:
I. The anterior spinocerebellar tract enters the cerebellum through the superior cerebellar peduncle, which defies this peduncle's role as an outflow pathway.
II. Select midline cerebellar tracts exit the cerebellum through the inferior cerebellar peduncle, which defies this peduncle's role as an inflow pathway.
Specifically, these midline pathways are the:
- Fastigiobulbar fibers, the fibers from the flocculonodular lobe to the brainstem vestibular nucleus, and certain monosynaptic cerebello-spinal connections.
pathways that pass through the cerebellar peduncles
- The MCP comprises corticopontocerebellar fibers, which are critical for the modulation of movement.
- Key fiber tracts of the ICP include the spinocerebellar tracts and the olivocerebellar fibers (known as climbing fibers).
- Three of the four spinocerebellar pathways enter the cerebellum through the inferior cerebellar peduncle: the posterior spinocerebellar tract, cuneocerebellar tract, and rostral spinocerebellar tract.
- The fourth spinocerebellar tract, the anterior spinocerebellar tract, defies the general organization of cerebellar inflow and enters the cerebellum through the superior cerebellar peduncle.
- Brainstem pathways that enter the cerebellum (other than the climbing fibers) through the inferior cerebellar peduncle are: the reticulo- and trigeminocerebellar fibers, and fibers from the vestibular nucleus and nerve, itself.
- Pathways that exit the cerebellum through superior cerebellar peduncle are the dentatorubal and dentatothalamic tracts, which project rostrally; the dentatoreticular tract, which projects caudally; and fibers from the globose and emboliform nuclei, which reach the region of the red nucleus responsible for the rubrospinal tract.
- In short, in regards to the inflow/outflow traffic of the cerebellum: the main inflow pathways into the cerebellum are the middle and inferior cerebellar peduncles and the main outflow peduncle from the cerebellum is the superior cerebellar peduncle.
The corticopontocerebellar pathway
- The clinical application of this pathway comes in the analysis of cerebellar deficits.
- Cerebellar injuries cause ipsilateral deficits.
- If a person has a cerebellar deficit (for instance, incoordination) due to brainstem injury, then either the ipsilateral cerebellum or a portion of this pathway (somewhere along its course) is affected.
- If the area of injury localizes contralateral to the side of the body that is affected, think of a corticopontocerebellar pathway lesion.
- The bulk of the pathway originates in the primary motor and sensory cortices; we exclude the lesser contributions from more wide-reaching brain regions.
- Nearly 20 million fibers are dedicated to the corticopontocerebellar pathway, whereas only 1 million fibers are dedicated to the corticospinal tract.
- The corticopontocerebellar fibers first descend to the pontine nuclei, where they make their primary synapse.
- The pontine nuclei project across midline through the MCP into the contralateral cerebellar cortex.
- The cerebellar cortex projects to the dentate nucleus, which lies deep within the cerebellum.
- The dentate projects fibers out of the cerebellum through the superior cerebellar peduncle, which cross midline within the midbrain, inferior to the red nucleus, to synapse in the ventrolateral nucleus of the thalamus and also in the red nucleus.
- The red nucleus projections typically originate from the globose and emboliform nuclei, which lie medial to the dentate nucleus, whereas the thalamic projections typically originate from the dentate nucleus.
- The thalamus projects back to the primary motor strip to complete the corticopontocerebellar pathway.
Clinical Case
Consider a stroke in which there is a left third nerve palsy and right-side hemiataxia.
- Where could the injury lie?
- How can we connect these disparate regions?
- Show fibers exit the right cerebellum through the superior cerebellar peduncle and pass adjacent to the third nerve fibers on the left.
- Indicate that injury here produces the aforementioned deficits.
- See Claude's Syndrome.
anatomy of the anterior cerebellum
We draw one of the saddle-shaped cerebellar hemispheres b/c the unfolded schematic of the cerebellum, which is so commonly used to represent the cerebellum, places the flocculonodular lobe at the bottom of the diagram, and we need to appreciate that the flocculonodular lobe actually lies in anterior, mid-cerebellar position.
- Above the fourth ventricle, we find the lingula: the slender vermian tip of the anterior cerebellar lobe.
- The lingula combines with the flocculonodular lobe to form the vestibulocerebellum.
- The cerebellar tonsils are a paired, midline structure that is an important aspect of a common neurologic condition, Chiari malformation.
arterial supply to the anterior cerebellum
Brain Atlas: Cerebellum
Clinical Correlation: Cerebellar Stroke
- Paired vertebral arteries derive the basilar artery, which branches into the paired posterior cerebral arteries.
- The posterior inferior cerebellar arteries (PICAs) emerge from the vertebral arteries.
- At the base of the basilar artery, paired anterior inferior cerebellar arteries (AICAs) emerge.
- At the upper portion of the basilar artery, the paired superior cerebellar arteries (SCAs) emerge.
On the anterior surface of the cerebellum:
- PICAs perfuse the inferior cerebellum
- AICAs perfuse the midlateral cerebellum
- SCAs perfuse the superior cerebellum.