The increased activity of the indirect pathway results in the hypokinetic disorder of Parkinson’s disease. The direct pathway is responsible for increasing cortical movement commands. Without that modulatory influence, the basal nuclei are stuck in the indirect pathway, without the direct pathway being activated. These neurons release dopamine into the striatum. Parkinson’s disease is the result of neurons in the substantia nigra pars compacta dying. Parkinson’s disease is a disorder of the basal nuclei, specifically of the substantia nigra, that demonstrates the effects of the direct and indirect pathways. (Image credit: "Cerebellar Peduncles" by OpenStax is licensed under CC BY 3.0) The inferior cerebellar peduncle arises from the medulla-specifically from the inferior olive, which is visible as a bulge on the ventral surface of the brainstem. The middle cerebellar peduncle is the ventral surface of the pons. The superior cerebellar peduncle projects into the midbrain. The connections to the cerebellum are the three cerebellar peduncles, which are close to each other. The major regions of the diencephalon are the thalamus itself, the hypothalamus, the epithalamus, which contains the pineal gland, and the subthalamus, which includes part of the basal nuclei (Figure \(\PageIndex\): Cerebellar Peduncles. The diencephalon can be described as any region of the brain with “thalamus” in its name. The diencephalon is deep beneath the cerebrum and constitutes the walls of the third ventricle. In the earliest vertebrate species, the cerebrum was not much more than olfactory bulbs that received peripheral information about the chemical environment (to call it smell in these organisms is imprecise because they lived in the ocean). The single exception is the system associated with olfaction, or the sense of smell, which connects directly with the cerebrum. Output from the cerebrum passes through the diencephalon. The rest of the brain, the spinal cord, and the PNS all send information to the cerebrum through the diencephalon. The etymology of the word diencephalon translates to “through brain.” It is the connection between the cerebrum and the rest of the nervous system, with one exception. The diencephalon is the one region of the adult brain that retains its name from embryologic development.