Cerebellum Anatomy Quiz

White Matter and Fibres of the Cerebellum

• The white matter of the two sides of the cerebellum is connected by a thin lamina of fibres related to the fourth ventricle.
• The upper part of this lamina forms the superior medullary velum, and its lower part forms two crescentic sheets called inferior medullary vela.
• Both the superior medullary velum and inferior medullary vela take part in the formation of the roof of the fourth ventricle.

Types of Fibres

• The white matter consists of two types of fibres: intrinsic and extrinsic fibres.

Intrinsic Fibres

• Intrinsic fibres remain confined within the cerebellum.
• They connect different regions of the cerebellum either in the same hemisphere or between the two cerebellar hemispheres.
• There are three types of intrinsic fibres:
• Projection fibres: connect the cerebellar cortex to the cerebellar nuclei.
• Association fibres: interconnect different parts of the cerebellar cortex.
• Commissural fibres: connect the two cerebellar hemispheres.

Extrinsic Fibres

• Extrinsic fibres connect the cerebellum with other parts of the central nervous system, including the brain and spinal cord.
• These fibres pass through three thick bundles called the cerebellar peduncles: superior, middle, and inferior.

Afferent Fibres

• Afferent fibres are of two types: mossy fibres and climbing fibres.
• Mossy fibres:
• Originate from the vestibular nuclei, pontine nuclei, and spinal cord.
• Terminate in the granular layer of the cortex within the glomeruli.
• Pass through granule cells to reach Purkinje cells.
• Climbing fibres:
• Represent terminations of axons from the inferior olivary complex.
• Pass through the granular layer and Purkinje cell layer to reach the molecular layer.
• Each climbing fibre becomes intimately associated with the proximal part of the dendritic tree of one Purkinje cell.

Efferent Fibres

• Efferent fibres are axons of Purkinje cells, which terminate in the cerebellar (central) nuclei.
• Some efferents from the flocculonodular lobe bypass the cerebellar nuclei and terminate in the brainstem nuclei.
• Axons of Purkinje cells are inhibitory to cerebellar nuclei.

Connections of the Cerebellum

• Afferent fibres terminate in the cortex.
• Efferent fibres arising in the cortex end in cerebellar nuclei.
• Fibres arising in the nuclei project to centres outside the cerebellum.
• The main afferent inputs to the cerebellum are proprioception, exteroception, vision, and from the vestibular apparatus.
• The main efferents from the cerebellum go via the thalamus to the cerebral cortex.