Answer
The diencephalon is one of the two secondary brain vesicles that derive from the forebrain. The thre major parts of the diencephalon are the thalamus, the hypothalamus ,and the epithalamus
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The thalamus ( one on each side) are large forebrain global structures that relay sensory impulses to the cerebrum. It also transmits motor impulses from the cerebellum to the cerebrum. Memory formation, and emotional processes of the limbic system also involve the thalamus
The hypothalamus is also situated in the forebrain-- it is located inferior to the thalamus. Functionally, and structurally, it is part of both the endocrine system and the nervous system. Several anterior pituitary regulating hormones are secreted by the hypothalamus; it also secretes the hormones oxytocin, and vasopressin (ADH) which are stored in the posterior (PP) pituitary gland. The hypothalamus is the primary control of the autonomic nervous system. As such, it exercises vital control over body temperature, and metabolism .
The epithalamus comprises the pineal gland and the habenula. The pineal gland is part of the endocrine system and secretes the hormone melatonin; melatonin is important in sleep cycle regulation.
The functions of the habenula are not clearly understood, but it is believed to have functions in limbic system processes,
A fourth part of the diencephalon, the subthalamus, is not of great physiological importance.
