Chapter 9 - Neurophysiology

Why do birds sometimes stand on one foot?

One reason is that holding one leg next to the body keeps it warm.

What is Homeostasis?

Refers to temperature regulation and other biological processes that keep body variables within a fixed range.

* A balanced internal state.
* Temperature and other biological processes that keep body variables within a fixed range.
* Think “thermostat”

_______, _______, and ________ are almost homeostatic but they anticipate future needs as well as reacting to current needs.

1. Temperature.
2. Hunger.
3. Thirst.

What is a Set Point?

A single value that the body works to maintain.

* EX: O2, H2O, Glucose, Protein, Fat, Sodium Chloride (NaCl, Salt).

\*\*\*\* Body Temperature is not quite ________.

Fixed

* It changes with the time of day, year, & other conditions.

What is an example of set point?

If a person has a calcium deficiency in their diet, the level of calcium concentration in the blood begins to fall below the set point - then storage deposits in bones release additional calcium into the blood.

On the other hand, if the calcium level in the blood rises above normal, they store excess calcium in the bones + excretes the rest.

What is Negative Feedback?

Processes that reduce discrepancies from the set point.

What is Allostasis?

The adaptive way in which the body anticipates needs depending on the situation, avoiding errors rather than just correcting them.

* EX: as the air warms up, a hiker increases in thirst & decreases urine production by the kidneys - anticipating probable sweating & possible dehydration.

Allostasis is the process by which the body responds to stressors in order to regain ______________.

Homeostasis.

How does the idea of allostasis differ from homeostasis?

Homeostasis is a set of processes that keep certain body variables within a fixed range. Allostasis is an adjustment of that range, increasing it or decreasing it as circumstances change.

Temperature regulation is a high ___________.

Biological priority.

What is Basal Metabolism?

The energy used to maintain a constant body temperature while at rest.

* We use about twice of our energy to do this.

What doe Poikilothermic mean?

(Amphibians, reptiles, and most fish) Their body temperature matches the temperature of of their environment.

* Sharks & tuna are the exception to the rule
* \*\*\*\*\*\*\*\*\*their body temperature matches the environmental temperature.

Poikilothermic animals lack ______________________ of temperature regulation like sweating or shivering.

Rather, they regulate their temperature ______________.

Physiological mechanisms.

Behaviorally.

What is an example of Poikilothermic animals?

A lizard moves between sunny and shady areas, or burrows to maintain a fairly steady body temperature.

What does Homeothermic mean?

(AKA endothermic)

Animals capable of generating body heat internally.

* \*\*\*\*\*\*\*\*\*\*\*\*use physiological mechanisms to maintain an almost constant body temperature despite large variations in the environmental temperature.
* EX: shivering, sweating → changes blood flow to the skin.

Although homeothermic, some species become poikilothermic during _____________.

Hibernation.

What is the normal body temperature for humans?

98\.6° Fahrenheit or 37° Celsius.

What temperature is the reason for concern in humans?

103° Fahrenheit for adults.

\*\*\*\*\*\*\* All physiological changes that defend body temperature depends on areas in the _________, specifically the _______________.

Hypothalamus.

Anterior Hypothalamus.

What area is most critical for temperature control?

The Preoptic Area.

Where is the preoptic area?

near the optic chiasm, where the optic nerves cross.

What does the Preoptic Area (POA)?

* Monitors body temperature by monitoring its own temperature.
* Cells in POA receive input from receptors in skin & spinal cord.
* Damage to this area → impairs one’s ability to regulate temperature.

If an experimenter heats or cools the POA in the brain, the animal will ____________ or __________.

Sweat or shiver.

What does the Preoptic Area and Anterior Hypothalamus do?

They send output to the hindbrain’s Raphe Nucleus (found in the brain stem) which controls shivering, sweating, heart rate, metabolism, blood flow, etc.

What is the primary advantage of maintaining a constant high body temperature?

A constant high body temperature keeps an animal ready for rapid, prolonged muscle activity even in cold weather.

Why did mammals evolve a temperature of 37° celsius (98° fahrenheit) instead of some other temperature?

Animals gain an advantage in being as warm as possible and therefore as fast as possible. However, proteins lose stability at temperatures much above 37° celsius (98° fahrenheit).

What are some sources of input to the Preoptic Area/Anterior Hypothalamus?

The Preoptic Area/Anterior Hypothalamus receives input from temperatures in the skin, the organs, and the brain including cells in the Preoptic Area/Anterior Hypothalamus itself.

It also receives prostaglandins and histamines when the immune system detects an infection.

How can an animal regulate body temperature after damage to their Preoptic Area/Anterior Hypothalamus?

It can regulate temperature through behavior, such as by finding a warmer or cooler place.

What evidence indicates that fever is an adaptation to fight illness?

The body will shiver or sweat to maintain its elevated temperature at a nearly constant level.

Also, fish, reptiles, and immature mammals with infections use behavioral means to raise their temperature to a feverish level.

Furthermore, a moderate fever inhibits bacterial growth and increases the probability of surviving a bacterial infection.

Fever increases body temperature usually caused by _________________.

Bacterial and/or viral infections.

Fever is the body’s ____________ against ____________.

Defense against illness.

When the body is invaded by bacteria, viruses, fungi, etc., ___________ are mobilized to attack them!

Leukocytes (white blood cells).

What do Leukocytes (white blood cells) release?

cytokines (protein) which, in turn, produces:

* Prostaglandin E1.
* Prostaglandin E2.
* Both of which increase body temperature and sleepiness.
* Can cross the blood brain barrier.

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This then excites receptors receptors in the preoptic area to direct the AND (autonomic NS) to raise body temperature.

Fever works because certain types of bacteria grows _______ at high temperatures & it ________ the activity of the immune system.

less vigorously.

enhances.

What is Vasopressin?

Released by the posterior Pituitary Gland, which raises blood pressure by constricting blood vessels.

What is Vasopressin also known as and why?

Antidiuretic Hormone (ADH) because it enables the kidneys to reabsorb water from urine and therefore make the urine more concentrated.

If you lacked vasopressin, would you drink like a beaver or like a gerbil? Why?

If you lacked vasopressin, you would have to drink more like a beaver. You would excrete much fluid, so you would need to drink an equal amount to replace it.

Would adding salt to the body’s extracellular fluids increase or decrease osmotic thirst?

Adding salt to the extracellular fluids would increase osmotic thirst because it would draw water from the cells into the extracellular spaces.

What is Osmotic Pressure?

The tendency of water to flow across a semipermeable membrane from the area of low solute concentration to the area of higher concentration.

What is Osmotic Thirst?

A drive for water that helps restore the normal state.

* Osmotic pressure draws water from the cells into extracellular fluid.
* caused by increased solute concentrations in body fluids and blood.

What is OVLT (Organum Vasculosum Laminae Terminalis)?

The area responsible for detecting osmotic thirst/pressure.

Osmotic thirst is best relieved by ________________.

Drinking H2O.

What is the Subfornical Organ (SFO)?

Brain structure adjoining the third ventricle of the brain, where its cells monitor blood volume and relay information to the Preoptic Area of the Hypothalamus.

Water constitutes ___% of a human’s body.

70%

The body needs enough fluid in the circulatory system to maintain normal __________.

blood pressure.

We maintain a constant amount of water in the body - by balancing the water ________ with the water we _______.

we lose.

take in.

How do we lose water?

* Sweating.
* Urinating.
* Defecations.

When the body needs water, the ________ releases vasopressin (hormone) which raises blood pressure by ______________.

posterior pituitary.

constricting blood vessels.

____________ enables kidneys to reabsorb water and secrete highly concentrated urine. (diuresis = urination)

Vasopressin (aka ADH - antidiuretic hormone)

What is Hypovolemic Thirst?

It is based on low volume of blood

* When blood pressure and blood volume are too low - the blood can’t cary enough water & nutrients to the cells.

What are the two ways the body can detect the loss of blood volume?

1. Baroreceptors → which are attached to large veins which detect the pressure of blood returning to the heart.
2. SFO (Subfornical Organ) → adjoining the 3rd ventricle; when blood volume drops, kidneys release RENIN, which converts to Angiotensin II, which constricts the blood vessels, which compensates for the drop in blood pressure.

How is Hypovolemic Thirst best relieved?

By drinking water with solutes.

What is the Supraoptic Nucleus?

Part of the Hypothalamus that controls the release of Vasopressin.

What is the Paraventricular Nucleus (PVN)?

Part of the Hypothalamus in which activity tends to limit meal size and damage leads to excessively large meals.

What is the Lateral Preoptic Area?

Part of the Hypothalamus that controls drinking.

What is the Angiotensin II?

Hormone that constricts the blood vessels, compensating for the drop in blood pressure; triggers thirst.

What is Sodium-Specific Hunger?

(aka Salty Cravings) When an animal becomes deficient in sodium, it shows an immediate, strong preference for salty tastes.

With Sodium-Specific Hunger, adrenal glands produce _______________________ (hormone) which causes….


1. ______________
2. ______________
3. ______________

to conserve sodium excreting more water fluids than usual.

Aldosterone.


1. Kidneys.
2. Salivary Glands.
3. Sweat Glands.

___________________________ triggers an increased preference for salty tastes.

Aldosterone.

Decreased ___________ increases blood levels of _________________, which increases salt cravings.

sodium.

Angiotensin II.

What are the two hormones that stimulate the craving for salt?

1. Aldosterone.
2. Angiotensin II.

What is Aldosterone?

Adrenal hormone that causes the body to retain salt.

Who would drink more pure water - someone with osmotic thirst or someone with hypovolemic thirst?

Someone with Osmotic Thirst would drink more water. Someone with Hypovolemic Thirst would drink more of a solution containing salts.

What is Lactase?

an enzyme that is necessary for metabolizing lactose, the sugar in milk.

What genetic difference is most important for variants in likelihood of drinking milk in adulthood?

Likelihood of drinking milk in adulthood depends largely on a gene that controls the ability to digest lactose, the main sugar in milk.

What evidence indicates that taste is not sufficient for satiety?

It is not sufficient because animals that sham-feed chew and taste their food but do not become satiated.

What evidence shows that stomach distension is sufficient in satiety?

If a cuff is attached to the junction between the stomach and the duodenum so that food cannot leave the stomach, an animal becomes satiated when the stomach is full.

What are 2 mechanisms by which CCK increases satiety?

When the duodenum is distended, it releases CCK, which closes the sphincter muscle between the stomach and duodenum.

CCK, therefore, increases the rate at which the stomach distends.

Also, neural signals from the intestines cause cause certain cells in the hypothalamus to release CCK as a neurotransmitter, and as its receptors, it triggers decreased feeding.

List the journey through the digestive system.

1. **Mouth** → food + saliva - which contains enzymes to help break down carbohydrates.
2. **Esophagus** → swallowed food travels down.
3. **Stomach** → it is mixed with hydrochloric acid + enzymes that digest proteins; It stores and digests food.
4. **Sphincter Muscle** → between stomach and intestines - periodically opens briefly to allow food to enter intestines.
5. Intestines


1. **Small Intestine** → \*\*\*\*\*\*\*\*\*\*main site for absorption of digested food into blood stream


1. Carried by the blood to body cells that use some nutrients + store the excess fat, glycogen, + protein.
2. Later…. these reserves are converted into glucose (body’s fuel)
2. **Large Intestine** → absorbs water + minerals. Lubricates the remaining materials to pass them as feces.

What is a Carnivore?

A meat-eater.

What is a Herbivore?

A plant-eater.

What is an Omnivore?

A meat/plant-eater.

What is the Splanchnic Nerves?

(Celiac Plexus (bundle of nerves) in the abdominal cavity)

Nerves that convey information about the nutrient contents of the stomach to the brain.

What is the Duodenum?

Part of the small intestine adjoining the stomach; \*\*\*\*\*\*\*\*first digestive site that absorbs nutrients.

What is the hormone Cholecystokinin (CCK)?

Hormone released from the Duodenum that constricts the sphincter muscle between the stomach and the Duodenum, limiting the meal size.

What is Glucagon?

Pancreatic hormone that stimulates the liver to convert stored glycogen to glucose.

What is Ghrelin?

Chemical released by the stomach during a period of food deprivation; also released as a neurotransmitter in the brain, where it stimulates eating.

What is Neuropeptide Y (NPY)?

Peptide that blocks the satiety actions of the Paraventricular Nucleus.

What is Agouti-Related Peptide (AgRP)?

Inhibitory transmitter that blocks the satiety actions of the paraventricular nucleus.

What is Melanocortin?

Type of chemical that promotes satiety.

Selection of foods:

1. Let your taste be your guide.
2. You prefer food that resemble familiar tastes or foods.
3. You learn the consequences of eating each food you try.

What is Conditioned Taste Aversion?

A phenomenon in which you eat something and, as a result, get sick.

* Your brain blames it on the food.
* \*\*\*\*\*\*\*pairing food with illness.

What is lactose?

The sugar in milk.

What is Lactose Intolerance?

Milk consumption causes gas / stomach cramping

* milk, cheese, ice cream, and other dairy products.

___________ adults (worldwide) cannot tolerate large amounts of milk-products - especially ________________, have low levels of lactose because of a recessive gene.

2/3 of adults.

Southeast Asians.

The urge to __________ is strong.

Chew.

The need to _________ is important to bring satisfaction from eating.

Taste.

A full stomach tells the brain that it is satisfied by way of the ________________________ and ___________________________________.

Vagus Nerve.

the Splanchnic Nerve.

What is Glucose?

Energy for the body, fuel for the brain.

The amount of glucose that cells receive vary depending on:

1. Insulin → enables glucose to enter cells using glucose for energy or storing it as fat or glycogen.
2. Glucagon → stimulates the liver to convert stored glycogen to glucose, thus raising blood glucose levels.

What occurs after we eat?

* Insulin Levels rise.
* Increase of glucose entering cells.
* Appetite decrease.
* Insulin reaches the brain + acts as a satiety hormone.

What occurs after we eat and time goes on?

* Blood glucose levels fall.
* Pancreas releases more glucogen + less insulin.
* Less glucose enters cells.
* Hunger increases,

What is Diabetes?

Blood glucose levels are too high.

Let’s talk about obese people and their insulin.

* They produce more insulin than people of normal weight.
* Increasing insulin causes more food than usual to be stored as fat.
* Therefore, their appetite returns soon after a meal.

What is the Lateral Hypothalamus?

Important area for control of feeding.

* lesion in this area leads to undereating.

What occurs when there is a lesion in the Ventromedial Hypothalamus (VMH)?

leads to overeating/weight gain.

What is Anorexia?

Characteristics:

* Low weight.
* Fear of gaining weight.
* Desire to be thin.
* Food restriction.

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Elevated levels of cortisol (OCD would be common in family members)

* Many depressed people also have increased cortisol.

What is Bulimia?

Characteristics:

* Binge/Purge.
* Normal Weight.

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Elevated levels of YY & PYY (neuromodulator/peptide)

* Lower levels of CCK (decreased receptor for serotonin)

Bulimia and Anorexia frequently run comorbidly with what three disorders?

* Depression
* Anxiety
* OCD