Sapolsky Chapter 2: Glands, Gooseflesh, and Hormones
I. The brain controls the endocrine system
A. The limbic system: a group of structures that form a border (limbus, in Latin) around the brain stem and are important for motivated behaviors and emotions.
B. Major components
1. Amygdala has several nuclei. It’s located in the depths of the temporal lobes on each side of the brain. The central nucleus has direct output to the sympathetic nervous system and is activated during aggression, fear, and anxiety. It is critical for learning associations between environmental stimuli with those “negative” emotions. Other nuclei in the amygdala are more important for sexual behavior, eating, and learning associations with more “positive” emotions.
2. Septal area also has several nuclei. It’s located more or less in the middle of the brain and forms the wall (septum, in Latin) between the 2 lateral ventricles. It primarily promotes “warm, fuzzy” emotions, including relaxation and sexual feelings.
3. Hippocampus (“sea horse” in Latin, because of its shape) stretches from the middle of the brain (above the septal area) down into the temporal lobes, ending adjacent to the amygdala. It is important for forming verbally-mediated memories in humans and spatial memories in rodents. It also processes some emotions. It has the lowest seizure threshold of the brain; some people with temporal lobe seizures have episodes of uncontrollable violence, if the seizure activity spreads to the amygdala.
4. The cingulate (girdle, in Latin) gyrus lies just above the corpus callosum—the bundle of fibers joining the two hemispheres. In cases of severe, long-lasting anxiety, surgical lesions are sometimes made in the anterior cingulate gyrus. It’s also involved in “working” memory.
5. Hypothalamus: “final common path” for emotions. 4Fs: feeding, fighting, fleeing, and reproductive behavior. Located on the floor of the brain, just behind the optic chiasm and above the pituitary, which it controls in two ways. (See below.)
II. Stress and the autonomic nervous system (ANS)
A. Sympathetic nervous system (Sapolski refers to the 4Fs of the symp. nerv. sys. as flight, fight, fright, and sex.) He says that the name comes from the “sympathizing of the brain with the viscera.” However, I read that it referred to the fact that the chain of sympathetic ganglia along the sides of the spine are all interconnected, and that therefore all organs controlled by the SNS act in sympathy (together). The SNS ganglia lie along the thoracic and lumbar parts of the spine.
1. Epinephrine (Greek for “on top of kidneys”) = adrenaline (Latin for “on top of kidneys”) It is released from the adrenal medulla after being stimulated by neurons of the SNS.
2. Norepinephrine (epinephrine lacking its methyl group) = noradrenaline. It is released by sympathetic nerves throughout the body. (See the diagram in Sapolsky, p. 21)
3. In general, the SNS speeds heart rate and breathing, increases blood pressure, directs blood away from the intestines and other digestive organs and towards the heart, brain, and working muscles.
B. Parasympathetic nervous system: located above and below the SNS, in the brain stem and sacral part of the spine. The PNS promotes digestion, growth, relaxation. Its neurotransmitter is acetylcholine.
C. While the 2 divisions of the ANS tend to be dominant at different times, there is definitely overlap. For example, during sexual excitement, the parasymp. NS is responsible for increasing genital blood flow and lubrication. However, at the same time, the SNS is increasing heart rate, breathing, blood pressure, and finally triggers orgasm/ejaculaiton.
III. Your brain: the real master gland
A. “Rejuvenation therapy” for aging men, using extracts of “glands” (i.e., testes), didn’t work very well, because testosterone is not soluble in water. (Sapolsky did not note that in the blood testosterone is bound to proteins that keep it dissolved in the blood. However, it’s not clear whether the testicular extracts had enough of those carrier proteins to do much good.)
B. So, what controls the glands? The pituitary! (from Latin term meaning mucus! Since the pituitary is located just over the nasal cavities, it used to be thought that it produced the mucus that flowed from the nose!) It’s sometimes referred to at the Master Gland.
C. But it’s the brain that is the REAL Master Gland. (How would you test this? See p. 27.)
D. How does brain communicate with pituitary?
1. Axons from neurons in hypothalamus (HTh) reach the POSTERIOR pituitary. When
the neurons in the HTh fire, oxytocin or vasopressin is released into blood from posterior pit. Oxytocin promotes smooth muscle contractions that lead to orgasm, childbirth, and milk let down during nursing. Vasopressin increases blood pressure and decreases the formation of urine—thereby conserving water.
2. Hormonal factors carried by blood from hypothalamus to ANTERIOR pituitary. P. 28: “Lots of scientists thought Harris’s idea was bonkers. …. Your brain oozing hormones? Preposterous!”
3. Contest between Roger Guillemin and Andrew Schally to isolate and identify releasing and inhibiting hormones. (stupendously difficult, because of the size of the tissue to be studied) They first collaborated, but then separated and came to loathe each other. (Like Coke vs. Pepsi!) Great Slaughterhouse war was on. Truckloads of brains were reduced to thimblefulls of liquid, which then had to be purified and repurified. 14 years later: 1st releasing hormone was discovered—thyroid releasing hormone. Shared Nobel prize in 1976. Independent confirmation: It might go faster if everyone worked together, but then they might share the same mistaken assumption.
E. Hormones of the stress response
1. Epinephrine and norepinephrine—from adrenal medulla and sympathetic neurons.
2. Glucocorticoids—steroids from the adrenal cortex. Help regulate blood levels of glucose.
3. These are controlled by CRF (corticotropin releasing factor) from hypothalamus to Ant. Pit.
4. Ant. Pit. then secretes ACTH (adrenocorticotropic hormone), which in turn triggers glucocorticoid release. (In humans, the primary glucocorticoid is cortisol.)
5. In addition, the pancreas is stimulated to release glucagon, which also raises blood sugar. (Opposite of insulin)
6. Secretion of some hormones is inhibited: testosterone, estrogen, progesterone, growth hormone, and insulin.
F. A few complications
1. Variability among species (transient increase in growth hormone in humans)
2. Time course: Maybe glucocorticoids mediate RECOVERY from the stress response.
3. Orchestration of hormones varies from stressor to stressor. (Symp. NS when subordinate animal is vigilant; glucocorticoid system when animal gives up. Similar to dichotomy between anxiety and depression)
4. Psychological context