Saturday, May 16, 2009

Basal Ganglia

The basal ganglia are a group of grey nuclei in the brain made up of neurons bodies which send their axons to interconnect with the cerebral cortex, thalamus and brainstem. The basal ganglia are associated with a variety of functions: motor control and emotions.

There are five individual nuclei that make up the human basal ganglia. The rostral basal ganglia is divided into the striatum, which contains the putamen and caudate nucleus, the external segment of the globus pallidus, and the internal segment of the globus pallidus. The caudal basal ganglia comprise the subthalamic nucleus and the substantia nigra. There are 2 sets of basal ganglia in the mammalian brain, mirrored in the left and right hemispheres.

The striatum is the main input zone for other brain areas to connect to the basal ganglia. Via the striatum, the basal ganglia receives input from the cortex, mainly from the motor and prefrontal cortices. The basal ganglia and cerebellum are large collections of nuclei that modify movement on a minute-to-minute basis. Motor cortex sends information to both, and both structures send information right back to cortex via the thalamus. The output of the cerebellum is excitatory, while the basal ganglia are inhibitory. The balance between these two systems allows for smooth, coordinated movement, and a disturbance in either system will show up as movement disorders.