Basal ganglia: Direct and indirect pathway of movement

The basal ganglia or basal nuclei is a structure located deep within the brain, and it’s made up of a group of nuclei - so millions of nerve cell bodies.

Put simply, the cerebral cortex decides how it wants to move the body and sends that input to the basal ganglia, and then the basal ganglia’s job is to help execute a smooth movement.

The basal ganglia are actually two pairs of deep structures - one on the left side and one on the right side of the brain.

Each pair consists of the globus pallidus, which has the internal globus pallidus and the external globus pallidus, and the striatum - which includes the caudate nucleus and the putamen.

The basal ganglia is linked to other brain structures, like the ventral anterior nuclei and ventral lateral nuclei of the thalamus, as well as the substantia nigra of the midbrain.

The basal ganglia can help start, stop, and control desired movements, while also inhibiting undesired movements.

As an example, when you walk, you have to move one leg at a time - so the basal ganglia help one leg to step forward, while inhibiting the other leg, so that it’s stationary - and that prevents you from falling!

Additionally, the basal ganglia is involved in perception.

Let’s take a look at this picture as an example. You can either see a rabbit - with its two long ears - or a duck, with its beak. And you can choose which animal to see, but you can’t see both simultaneously, because the basal ganglia stimulates the vision of one, while it inhibits the vision of the other one. For this reason, the brain can only perceive one image at a time.

For the basal ganglia to work, nearly the entire cerebral cortex projects onto the striatum.