Diencephalon of the brain
Surrounded by the cerebral hemispheres, the diencephalon forms the core of the forebrain and consists largely of the thalamus, hypothalamus, and epithalamus.
Thalamus: The thalamus consists of bilateral egg-shaped nuclei which are usually connected by an interthalamic adhesion (intermediate mass). It is the most important relay station for information coming into the cerebral cortex. It is composed of a large number of nuclei, each with its own functional specialty and projecting fibers connecting to and from specific regions of the cerebral cortex. The thalamus sorts and edits information by sending impulses relating to similar functions as a group to the appropriate sensory cortex. Almost all inputs going to the cerebral cortex have to pass through the thalamus, including sensation, motor activities, cortical arousal, learning, and memory.
Hypothalamus: The hypothalamus forms the cap of the brain stem and the inferolateral walls of the third ventricle. Its mammillary bodies bulge anteriorly and are relay stations in the olfactory pathways. The infundibulum runs between the optic chiasma and the mammillary bodies and connects to the pituitary gland. The hypothalamus is the primary visceral control center for the body and is critical in the maintenance of the body's homeostasis. Its primary homeostatic roles are:
1. Autonomic control center: The hypothalamus controls the activity of centers in the brain and spinal cord which directly influence blood pressure, rate and force of heartbeat, digestive tract motility, eye pupil size, and other visceral activities.
2. Center for emotional response: Lying at the heart of the limbic system, the hypothalamus is heavily involved in the perception of pleasure, fear, rage, and biological rhythms and drives. As a result of this, it is also responsible for most physical expressions of emotion.
3. Body temperature regulation: Initiates cooling and heating activities based on blood temperature and thermoreceptors throughout the body.
4. Regulation of food intake: The hypothalamus detects levels of certain nutrients and hormones in the blood to regulate feelings of hunger.
5. Regulation of water balance and thirst: When detected levels of body fluids become too concentrated, the hypothalamus triggers the release of antidiuretic hormone by the pituitary to force the kidneys to retain water and trigger feelings of thirst.
6. Regulation of sleep-wake cycles: Sets the timing of the sleep cycle in response to daylight-darkness cues received from visual pathways.
7. Control of endocrine system functioning: Controls the secretion of hormones by the pituitary and produces hormones of its own.
1. Autonomic control center: The hypothalamus controls the activity of centers in the brain and spinal cord which directly influence blood pressure, rate and force of heartbeat, digestive tract motility, eye pupil size, and other visceral activities.
2. Center for emotional response: Lying at the heart of the limbic system, the hypothalamus is heavily involved in the perception of pleasure, fear, rage, and biological rhythms and drives. As a result of this, it is also responsible for most physical expressions of emotion.
3. Body temperature regulation: Initiates cooling and heating activities based on blood temperature and thermoreceptors throughout the body.
4. Regulation of food intake: The hypothalamus detects levels of certain nutrients and hormones in the blood to regulate feelings of hunger.
5. Regulation of water balance and thirst: When detected levels of body fluids become too concentrated, the hypothalamus triggers the release of antidiuretic hormone by the pituitary to force the kidneys to retain water and trigger feelings of thirst.
6. Regulation of sleep-wake cycles: Sets the timing of the sleep cycle in response to daylight-darkness cues received from visual pathways.
7. Control of endocrine system functioning: Controls the secretion of hormones by the pituitary and produces hormones of its own.
Epithalamus: The epithalamus forms the roof of the third ventricle and is the most dorsal portion of the diencephalon. The pineal gland extends from its posterior border. The primary function of the pineal gland is to produce melatonin, which is a sleep-inducing signal that helps regulate the sleep-wake cycle.