The subcortical structures of the nervous system have complex motor and non-motor functions. They are situated beneath the cerebral cortex, and receive extensive inputs from it and the peripheral sense organs and stretch receptors. Through recurrent feedback loops, the information received is processed and integrated to provide an output that contributes to scaling, sequencing, and timing of movements, in addition to learning and automatization of motor and non-motor behavior. The subcortical structures include: the limbic system, the diencephalon, and the ventricles.
The limbic system is comprised of telencephalic, diencephalic, and mesencephalic components that are located on both sides of the thalamus. It includes the large subcallosal cingulate and parahippocampal gyri of the medial surface of the cerebral hemisphere, as well as the hippocampal formation formed by the hippocampus proper, the dentate gyrus, the subicular complex and area 28 of the cortex. These structures are related to the terminations of the olfactory tracts in the frontal and medial temporal lobes. The limbic system is also associated with the subcortical nuclei, which includes the amygdala, the septum, the hypothalamus, the habenula, the anterior thalamic nuclei and parts of the basal ganglia. It is involved in emotional and behavioral processes, motivation, long-term memory, and olfaction.
The diencephalon is part of the forebrain, and it consists of the thalamus, the hypothalamus, the epithalamus, the subthalamus, and the metathalamus.
The thalamus is an ovoid mass of gray matter, situated on each side of the third ventricle. It is responsible for relaying sensory and motor signals to the cerebral cortex, as well as regulating consciousness, sleep, and alertness.
The hypothalamus lies beneath the thalamus, and is bordered laterally by the subthalamus, the internal capsule, and the optic tract. It is comprised of the optic chiasma region, the tuber cinereum, the tuberal eminences, and the stalk of the pituitary gland, in addition to the mammillary bodies and the posterior perforated substance. The hypothalamus’ main function is to control fluid and electrolyte balance, food ingestion, energy balance, reproduction, thermoregulation, as well as immune and emotional responses.
The epithalamus is comprised of the anterior and posterior paraventricular nuclei, the medial and lateral habenular nuclei, the stria medullaris thalami, the posterior commissure, and the pineal body. It connects the limbic system to other parts of the brain, and secretes melatonin and other hormones from the pineal gland that are involved in the circadian rhythm. Moreover, the epithalamus contributes in the regulation of motor pathways and emotions.
The subthalamus consists of complex nuclear groups and fiber tracts. This mainly includes the subthalamic nucleus, a large nucleus situated above the substantia nigra, medial to the internal capsule. The subthalamus plays a role in motor control.
The metathalamus is comprised of the medial and lateral geniculate bodies, and is associated with vision and hearing.
The ventricular system of the brain is formed by a series of interconnecting spaces and channels that are derived from the central lumen of the neural tube and the cerebral vesicles which gave rise to it. It includes two lateral ventricles, a third and fourth ventricle, and a cerebral aqueduct. These cavities produce cerebrospinal fluid (CSF), which flows and circulates to bathe and cushion the brain and spinal cord within their bony confines.