Pyramis of vermis

At a glance

English

Pyramis of vermis

Latin (TA2)

Pyramis vermis

System

Brain and spinal cord

Region

Head

Side

Single, on the midline

About the pyramis of vermis

The pyramis is one of the segments of the vermis, the narrow midline strip that joins the two cerebellar hemispheres. It lies on the inferior surface of the cerebellum, in the posterior lobe, and is lobule VIII in the numbered scheme. Seen in a midline section, it forms a pyramid-shaped block of folia pointing into the white matter, which gives it its name.

Its boundaries are two fissures. In front and above, the prepyramidal fissure separates it from the tuber of the vermis. Behind and below, the secondary fissure separates it from the uvula. On each side it is continuous with the biventral lobule of the hemisphere, and the pyramis and the two biventral lobules together form one transverse band across the underside of the cerebellum. It lies in the vallecula, the midline hollow between the hemispheres, above the cisterna magna.

Like other parts of the vermis, it belongs to the spinocerebellum. It receives fibres from the spinal cord carrying information about the position and movement of the body and limbs, and it holds part of a second map of the body. Its output passes mainly through the fastigial nucleus to brainstem centres that control posture and the muscles of the trunk and limbs.

Disease of the vermis gives unsteadiness of stance and gait rather than clumsiness of individual limbs. The pyramis and nearby lobules are supplied mainly by the posterior inferior cerebellar artery, whose vermian branches run on this surface; an infarct in that territory can therefore cause sudden truncal unsteadiness and vertigo.

Function and supply

Function

Part of the spinocerebellum; helps control posture, balance and the trunk and limb muscles.

Blood supply

Vermian branches of the posterior inferior cerebellar artery.