Thalamus and hypothalamus are both names of structures in the brain. While the hypothalamus is cone-shaped, the thalamus consists of two connected lobes, one located in each hemisphere. The hypothalamus regulates the body's vital metabolic processes, affecting temperature, blood pressure, hunger, thirst and sleep. It controls the endocrine system by affecting the pituitary gland's production of hormones. The thalamus takes information from a number of different areas of the brain and relays it to the cerebral cortex, the outer layer of gray matter where higher level brain functions take place.
In both structure and function, the thalamus and hypothalamus are quite different, but the names seem confusingly similar. The names are similar because hypo means under, and the hypothalamus was named for its position, which is below the thalamus. Both thalamus and hypothalamus are part of an area of the brain known as the diencephalon.
The function of the hypothalamus in maintaining the body's normal state is known as homeostasis. A person's weight, temperature, blood pressure and fluid balance are all regulated as part of this process. The hypothalamus receives information about different parts of the body via the nervous system, enabling it to stimulate changes that bring systems back into balance.
Information about factors such as blood pressure, the skin's temperature, gut fullness, and the concentrations of various substances in the blood is received by the hypothalamus, which may then activate the autonomic nervous system or the endocrine system. Through the autonomic nervous system, responses involving sweating, heart rate, digestion and narrowing of blood vessels can be used to alter the body's state. The hypothalamus controls the endocrine system through the pituitary gland, stimulating it to produce hormones that affect glands such as the thyroid and the adrenals. This allows it to alter metabolism, blood pressure and the release of adrenaline.
Both sensory, which means from the senses, and motor, or movement, information are relayed by the thalamus to the cortex. Sensations such as pain, information from the gut and emotions are all transmitted through the thalamus. Information regarding the sense of smell is different from that of the other senses, as it only reaches the thalamus after it has been received by the cortex. Circadian cycles, such as sleep wake cycles, are partly regulated by the thalamus. As the hypothalamus is also concerned with sleep wake cycles this is one area where input from both thalamus and hypothalamus is involved.