Brain Anatomy

So far, we have discussed the cerebral cortex almost exclusively--the frontal, temporal, parietal, and occipital lobes are all part of the cortex. While the cerebral cortex does house most complex functions, other subcortical structures of the brain also serve important purposes. The diencephalon lies in the center of the brain, surrounded by the cortex. It is made up of the thalamus and the hypothalamus, two vital operating centers for the nervous system. The thalamus relays signals to various areas of the brain, while the hypothalamus regulates vital body functions like and temperature and water balance.

The thalamus, which lies directly rostral to the brainstem (see figure), is commonly referred to as the relay center of the brain. It can receive body-to-brain input, send brain- to-body output, or make connections between different parts of the brain. Sensory neurons carry information from the body to nuclei in the thalamus, and the thalamus sends those signals to areas in the cerebral cortex, like the somatic sensory area. Other nuclei in the thalamus receive signals from higher parts of the brain, like the primary motor cortex, and relay commands to the movement-control centers of the brainstem. Other centers in the thalamus interconnect various areas in the cortex with one another, allowing the brain's many parts to work together smoothly.

The hypothalamus is located near the pituitary gland, in the center of the brain. The hypothalamus is divided into three sets of nuclei, which perform separate functions but are highly interconnected. The medial zone nuclei work together with the mammillary body, a tiny nearby structure, to control essential, instinctual behaviors such as feeding, reproducing, and parenting. The medial zone also regulates internal temperature and water balance. It receives input from the limbic system, which is highly involved in the circulation of hormones, and from the sensory nuclei in the brainstem. The periventricular zone nuclei control secretion of hormones by acting on the nearby pituitary gland to stimulate or inhibit hormone release. Neurons from the periventricular zone can secrete other hormones, such as oxytocin and vasopressin, directly into the bloodstream. The periventricular zone is also responsible for modulating circadian rhythms. The lateral zone of the hypothalamus is actually not organized into nuclei; rather, its neurons are scattered, and are often considered to be part of another nearby structure, the midbrain reticular formation. Overall, the hypothalamus is most commonly associated with its role in hormone regulation.