Anatomy clinical correlates: Cerebellum and brainstem

The cerebellum, which is  latin for ‘little brain’, is a part of the brain that plays a major role in posture, balance, maintenance of muscle tone and coordination of skilled voluntary motor activities. The brainstem, on the other hand, is a trunk-like structure that connects the higher parts of the central nervous system with the spinal cord and serves as a center for life sustaining reflexes, such as breathing and our heartbeat. Injury and disease to these parts of our brain can result in a variety of complex neurological problems, which can even have life threatening consequences. 

First off, let’s look at lesions of the cerebellum, which can be caused by a variety of things such as stroke, space occupying lesions, infections, or drug toxicities. Remember that the cerebellar cortex can be divided into three functional regions that are positioned longitudinally: the lateral zone; the intermediate or paravermal zone; and the median or vermal zone. 

One type of lesion is a lateral lesion of the cerebellum, which affects the lateral and intermediate zone of the cerebellum and their associated cerebellar nuclei, which impairs voluntary movements of the extremities. Think Lateral lesions affect Lateral structures! The lateral zone assists in motor planning, and the intermediate zone has been shown to control muscles of the distal parts of the limbs, particularly the hands and feet. 

Clinically, lateral cerebellar lesions can cause ipsilateral limb ataxia, meaning loss of coordination of the limb on the same side as the lesion. This can manifest as: intention tremor, which are involuntary, trembling movements that occur with voluntary targeted movements; dysmetria, which is when individuals overshoot or undershoot an intended position of the extremities for example during the finger to nose test; dysdiadochokinesia which is the inability to perform fast alternating movements; a loss of balance with a tendency to fall to the same side as the lesion, and finally reduced muscle tone on the ipsilateral side.