Word: hypothalamus
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...notion that 90% of sex is in the mind is literally true: the parts of the brain involved in sexual response include, at the very least, the sensory vagus nerves, the midbrain reticular formation, the basal ganglia, the anterior insula cortex, the amygdala, the cerebellum and the hypothalamus...
When the brain detects a threat, a number of structures, including the hypothalamus, amygdala and pituitary gland, go on alert: they exchange information with each other and then send signaling hormones and nerve impulses to the rest of the body to prepare for fight or flight...
Each of these compounds is slightly different, and scientists are just beginning to figure out how they all work together (see diagram). What is clear is that all of them are important nodes along an elaborate network of interconnecting pathways that feed into, and out of, the hypothalamus, a brain structure that is the control center for weight regulation. The body produces hormones that activate the hypothalamus. The neurons in the hypothalamus send new messages back to the body. And just like subliminal messages spliced into a filmstrip, these signals powerfully affect our behavior even when we are not aware...
Thus, while we read the paper or carry on a conversation, the hypothalamus--activated by leptin or some other compound--orders cells and tissues to ratchet up energy expenditure. The body responds by idly fidgeting to raise metabolic rates, or by increasing blood flow to the outer layers of the skin in an effort dissipate heat. In this way, we carry out a process known as thermogenesis, which is the body's way of burning excess calories...
Leptin, which exercises an influence on appetite and thermogenesis, is thought to be key to maintaining this balance. For as we layer on fat, we pump out more leptin, which signals the hypothalamus that it's time to accelerate energy output and brake caloric intake. The problem is, people who gain weight have now been shown to develop a remarkable resistance to leptin's power. The fatter they get, and the more leptin they make, the more impervious the hypothalamus becomes. Eventually the hypothalamus interprets the elevated level of leptin as normal--and forever after misreads the drops in leptin...