9. (41-42) Independent CNS Controls of Breathing, Cardiovascular, Food & Drink and Final Words on the Brain's Workings

9.41 Autonomic Brain Control of the Vital Functi
Update 07 Oct. 2021. The below descending column shows contents of the chapter in order of the reading. Use search & find to got directly to your particular interest.

The autonomic nervous system (ANS) has been dealt with under the Peripheral Nerves

Respiratory Control 

Cardiovascular Control

Food and Drink Control

Time Control - The Clock of Our Body 

sleepiness and alertness 

Sexuality 

The Glands 
Rewards. Motivation, Aversion, Addiction

The autonomic nervous system (ANS) has been dealt with under the Peripheral Nerves because it was initially seen as the nerves that exit from the intermediate gray matter of the spinal cord and from the cranial nerve ganglia at the outer edge of the brainstem. So it was felt to be independent of the central nervous system (CNS). But now we know that its peripheral part is a combination of the sensory and effector transmission of a loop of functions that need central automatic control, independent of conscious decision-making. The loop is closed by a series of neuronal nuclei in the brainstem, medulla and pons, the midbrain and the diencephalon taking orders from neuronal nuclei in and around the hypothalamus (a diencephalon structure) and engaged in a coordinated action to pass electrical and chemical signals back and forth between the periphery to the center. More specifically, the afferent (toward the center, and CNS-directed signaling) part of the ANS runs from the vital organs to combine mostly in cranial nerves V, VII, IX  and X and provide the sensory data of the vital organ functions such as respiratory, cardiovascular, GI tract and eating, renal and water & electrolytes, memory, and time telling. These major sensory nerves pass the information from their distal receptors in the organ systems back up the sensory branches into the nucleus of the tractus solitarius (NTS) located in dorsal medulla of the brainstem.

Figure below: Cranial Nerves VII, IX and X shown encircled by small and larger black and white closed loops just as they form the nucleus of the tractus solitarius (purple thin rodlike structure) in the dorsolateral medulla. (Note the pons as the forward rounded structure and connected with the upper border of medulla, and note the midbrain just above, connected to the upper pons)

The solitary tract (tractus solitarius) is formed from fibers of the inferior ganglion of the vagus X nerve, geniculate ganglion of the facial VII nerve, and glossopharyngeal IX nerve. The tract travels along the lateral aspect of the dorsal nucleus of the vagus nerve before ending the solitary nucleus.

 The NTS is constantly receiving information like the blood oxygen, CO2 and pH level, the heart rate, the blood pressure fluctuations, the state of nutrition based on blood glucose, the electrolyte and water balance, the body timing rhythm and other vital information that helps its autonomous decision-making. Note "autonomous" here means free of conscious control and it operates day and night, sleep and wake, coma and alert.

Respiratory Control is located in several parts of the medulla. The "several" is important because it provides protection against complete loss of respiratory function by damage to a single nucleus. One respiratory center located in the ventral medulla controls inspiratory respiration. (breathing in) And it is very sensitive to stoppage by opioid drugs, being the cause of death from opioid overdose. Another respiratory center is in the higher part of the dorsal medulla and it controls muscles of expiratory respiration (breathing out) that become useful for Olympic style runners and it is not sensitive to opioids. Damage involving a complete cut of the lower medulla anywhere from just below the respiratory center to the upper cervical spinal cord results in deadly loss of breathing and needs a mechanical ventilator. It is a common cause of injury from diving in shallow water or being thrown on one's head from a horse. (The former TV Superman)

Cardiovascular Control is located in a nucleus of the hypothalamus. In contrast to the respiratory system which totally depends on CNS control, the cardiovascular system can run in the absence of nervous system control and we see that in fact in heart transplants. But autonomic nerves modulate the heart rate and the blood pressure in response to changes in the environment allowing long distance runners to automatically keep the body tissues supplied with maximum oxygen and glucose, and this autonomic modulation can also be a cause of diseases like hypertension and deadly cardiac arrhythmia. 

Food and Drink Control is also in the hypothalamus in its own nuclei. Feedback from CN X informs the hypothalamus the state of the stomach - full, empty, high- or low-calorie.  The frequency of eating is determined by these sensory cues, mainly summing up to hunger rising as time from last eating lengthens.

Time Control - The Clock of Our Body is located in the base of the hypothalamus atop the famous crossing (chiasm) of left and right optic nerves, hence the suprachiasmatic (optic crossing) nuclei (SCN; plural because there are 2 of them). Each single neuron in the SCN is literally a ticking clock. 
   Although it is not really necessary for you, the reader, to understand the actual basis of a neuron cell being a "ticking clock", reference to the below figure with following explanation might be interesting. Note in the figure, first of all, the cell nucleus which is so labeled at its bottom part, and notice the 2 ovals, the white CLK (Clock gene) and dark gray CYC (Cycle gene), which are genes for time telling function. As shown, these 2 genes are next to and attach to each other. And the combination makes a chemical reaction that produces their protein products tim (time) and per (period), which you see to the right of the genes inside the rectangles, and those proteins defuse out of the nucleus into the cell body, as you may see, forming a duo (dimer). This combination acted upon by phosphorylation and phosphating enzymes defuses back into the nucleus and acts as inhibitory agent (slows down) the reaction of the CLK and CYC. This whole loop results in a cyclic set of chemical reactions implied by the pointer to the zigzag line showing the nuclear gene product of TIM and PER. This timing works out over a full day to a circum-24-hour (circadian) rhythm and the chemical reactions are affected by the degree of night and day that the animal or person composed of these cells experiences. Thus, the ticking clock. Finally, it is astounding to note that every living organism in the animal world from single cell bacteria to the most complicated human has these ticking clock cells which set the rhythms of an organism's life. How it all started, all I can say is, Go figure? 
 
And the thousands of similar cells ticking are coordinated by chemical mediators into a single rhythm that is slightly longer than 24 hours, hence circadian (circa approx. a day). This time schedule is transmitted by effector nerves to every cell in the body and makes for the rhythm of our lives, i.e., makes us feel sleepy, sexual, hungry, thirsty etc. more than usual during particular times of day, and in humans it times reproduction for once a month in a woman. 
Note that the clock of our cells affects sleepiness and alertness and determines our sleep and wake times. Thus the problems of jet lag and late night shift work are, essentially problems of the autonomic system controlled by nuclei in and around the hypothalamus. Damage to the anterior hypothalamus causes sleeplessness while damage to its opposite end, the posterior causes a sleeping sickness. 

Sexuality: Here we want to differentiate between gender - male and female - which is based on a person's outer appearance but often correlates with the 23rd pair xx chromosome for female and xy chromosome for male.  Note the determiner of chromosome gender is the male, who produces 50% x or y single chromo sperm that fertilizes the female ovum which only produces x single chromo ova. A person's outer appearance can, of course, be produced by makeup and dressing but his or her basic behavior sexuality comes from brain patterning whereby sexuality neurons in the hypothalamus are affected by exposure to varying amounts of male hormone (testosterone) or female hormone (estradiole) in the mother's womb. Experimental data in lower animals (rats and mice) have shown that homosexual behavior in offspring can be caused by exposing the pregnant mother of the offspring to higher than usual levels of either testosterone (or other masculinizing chemical) to make male-behaving female homosexuals) or estradiole (or other feminizing chemical) to make male homosexuals.  I am aware that this is a highly controversial area which the "gay" vehemently denies. Note this is not necessarily the only cause of an individual's homosexuality but it is an important one because it suggests prevention (or enhancement) and also why homosexuality seems so common today. It should make potentially pregnant women very sensitive to environmental chemicals or medications that have sex hormone affects, eg, muscle-building sports meds that are male sex hormone.

The Glands in the body from the master pituitary gland at the base of the brain on down to the thyroid, reproductive, stress (adrenal cortex), metabolic (insulin and growth hormones) and time telling (pineal gland and melatonin) are under central control from hypothalamic nuclei cells, several types of which secrete releasing hormones (thyroid, cortico, etc.). Again this is an autonomous function meaning no conscious control, automatic but based on feedback from the Cranial Nerve sensory branches and NTS.

Rewards. Motivation, Aversion, Addiction are connected behaviors that are under the autonomic nervous control involving many nuclei in and around the hypothalamus, in a widening circle connected on the median (inside) surface of the brain hemispheres that has been called the Limbic Lobe (Limbus from the Latin "bordering" implies a circular outline, a looping signal-way)
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