The cerebellum is a part of the brain located just above the brainstem towards the back of the head. It is divided into two parts: the cerebellar cortex and the deep cerebellar nuclei. The cerebellar cortex is comprised of three layers. The outermost layer, called the molecular layer, is composed of the stellate and basket cells which are two types of inhibitory interneurons. The middle layer is called the Purkinje Cell Layer, which gets its name from the Purkinje cells which are found there. The Purkinje cells send inhibitory messages to the deep cerebellar nuclei. Each of these cells receives synapses (impulses) from roughly 100 000 axons of the granule cells from the cerebellar cortex. The innermost layer is called a granular layer, which is made up of granular cells that sense impulses from outside the cerebellum and sent outputs to other cells inside the cerebellum. The directions for the cerebellar functions are sent from the primary motor cortex to the spinal cord, which are then received by the cerebellum from the cerebral cortex, visual cortex and somatosensory cortex. The cerebellum is partitioned into the anterior lobe, the posterior lobe and the flocculonodular lobe, between which the primary and posterior lateral fissures run. Although the cerebellum appears small, it contains half of the neurons in the brain and is responsible for guiding movement based on sensory feedback (mostly visual), directing attention, measuring time and other cognitive operations