Brain and Motivational States:Homeostasis, Temperature Regulation, Ectotherms

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Neurological Basis of Behavior (PSY - 610)

Lesson37

Brain and Motivational States

Objectives:

To familiarize the students with the

Process of homeostasis, the biological systems,

The brain modulation of these systems

And how the body's systems can compete with each other for the survival of the organism.

Brain and motivational states

Homeostasis, include temperature regulation, Hunger, thirst, bio-rhythms, Sleep and awakening.

Pathology related to sleep cycles

Sleep disorders and treatment

Homeostasis:

A balance and an optimal functioning system of the body have to be maintained for survival of the

organism. Therefore, there are well defined and in most cases autonomous neurological feedback

systems which work to maintain an internally stable environment of living organism. There are feed

forward systems, feedback systems that are constantly monitoring and informing each other of the status

(think of very efficient information systems of the computer or an organization) the brain areas and

organs are kept informed of each other's status. For example, the somatosensory systems- the skin

sensors send temperature information to the receptors in the brain and the temperature receptors would

send out messages for making appropriate adjustments. However, the receptors do not exist only on the

outside but also within the brain. "It is only against a homeostatic background that other more active

systems can function, and many of an animals activities are motivated by the homeostatic

needs,"(Bridgeman 1988, p 237). Homeostasis has evolved to support survival by maintaining optimal

functioning, if any problems the whole system needs readjustments. If these are minor the systems

would sustain it and make the changes, however, if major changes are required and cannot be made

these may lead to death.

Actions and behaviors are motivated by the homeostatic requirements (which are signals of the body's

needs). Behaviors are programmed to respond to the needs of homeostasis and motivated drives.

There are internal receptors, external receptors/stimuli, brain mechanisms, neurochemical regulatory

systems and these are all well synchronized. During the process of evolution receptors evolved for

specialized functioning such as for temperature regulation, hunger (and nutrient, glucose, fat

monitoring), thirst,(fluid and salt levels), sleep (awakening and sleep need). We will discuss these four

in detail

Temperature Regulation:

Temperature regulation is a motivated behavior in that it has all the important characteristics of

motivated behaviors- According to Mogensen (1980) temperature regulatory behavior is purposive (the

goal to warm or cool the body) persistent (behavior would continue till the goal has been reached) has

periodicity (winters nest building, fur or hibernating,) and prioritized .

Temperature regulation is a fairly well defined system and the evolution of human temperature system

is quite well laid out (and so it is in other animals). This is an important evolution for maintaining

optimum body functioning. As the evolution of varied species took place on land and sea, tropics or

Iceland, Equator or the Poles emerged the development of a strong and sensitive thermoregulatory

system for their needs became necessary for survival

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Ectotherms:

Amphibians, Reptilians depend on their external environment for temperature regulation. These animals

are not cold blooded but adjust by relocating to an environment. These may be called solar powered

animals, who gain heat from the sun and solar heated places. However, they cannot remain in places

which are too hot or too cold (if too hot outside, they burrow holes and stay in those holes, if too cold

they come out in the sun). These animals have also evolved vasoconstrictors and vasodilators on the

skin (vasoconstrictors contract blood vessels so less energy needed to be expended). The animals remain

in a state of stupor in the cold--not very efficient workers with this state. In a laboratory in the US

where I worked, lizards used in an experiment were anesthetized by keeping them in ice, and surgery

could be carried out- and when warm they would come out of this state. This kind of a response in the

amphibians and the reptilians is directly controlled by the thermoregulatory receptors in the

hypothalamus and the brain and is dependent on the environment.

Endotherms:

Mammalians and birds have evolved an effective temperature control system- a set point around which

the body functions like the thermostat of air conditioner or oven. The endotherms have their own

internal controls.

Set point:

An internal point: temperature or standard that the body functions to maintain by cooling or heating

through homeostasis (increase or decrease metabolism).

There is a neutral zone range around the set point within which the internal temperature can vary a few

degrees higher or lower but not more than that. If the temperature rise or drop beyond the range (more

or less) than the thermo regulatory mechanisms for cooling or heating are activated and the metabolism

works to meet the required (heat up or cool the body).

Because of their regulatory capacities, the mammalian species and birds can manage continued activity

for longer periods as compared to reptile (when faced with the temperature challenges. Higher activity

and metabolism challenges can be sustained--have a higher threshold.

Like the ectotherms, endotherms can also use changes in the environment.

Environmental adjustments are made

a) To cool the body. Humans and other animals use shades of trees. The body's response is perspiration:

dogs perspire through tongue, horses through skin, and humans through specifically active glands.

Humans also wear clothes which allow ventilation of heat. In addition humans have invented fans and

air conditioners to cool themselves, and

b) To heat the body through external sources such as shelter, fire, covering for heat conservation,

huddling together in animals ( especially young) and in humans warm clothing, hot beverages high

energy providing foods and warm and heated homes (from fire)

Heat production:

What does the body do when heat is needed to be generated? There is Increase in the basal metabolism,

increase in muscular activity, shivering, and increase in the sympathetic systems (increased heart pulse

rate, adrenaline, and thyroid release)

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Heat loss:

Heat needs to be radiated away from the body (form the inside) one mechanism is evaporation through

sweating, and conducting the heat out through other sources Conduction through taking a bath--dogs ,

buffaloes and other animals stay in water during hot days.

(References; Bridgeman 238-260, Mogensen 58-75)

Response to cold is constriction of blood vessels in the periphery for maintaining the internal core

temperature at a constant, and reducing loss of heat through radiation (to the outside). This is why we

have cold hands and feet in winter, and which is why the mountain climbers often loose their fingers

and toes because of freezing. Fur bearing animals also respond by pilo erection (raising the fur on their

body), and birds do it by fluffing their feathers. The skin sensors important as they also provide

information of heat and cold

Though behavioral responses like seeking heat when cold or taking a bath when hot are mechanisms for

temperature control, the physiological and brain mechanisms take a priority

Brain /neural substrates of thermoregulatory behavior

Preoptic area in the anterior hypothalamus is the master control in both heating and cooling

mechanisms. Heating this area leads to sweating, and cooling it leads to shivering, both these are body's

reaction to thermoregulatory challenges.

The lower phylogenetic areas involved in thermoregulation are in the brain stem(which are under the

hypothalamic control and the spinal cord, but the range of the spinal neutral zone (about 2-3 degrees) is

too wide and therefore primitive (not refined) as the organism can die of hypothermia (cold: freeze) or

hyperthermia (heat: heat stroke), before the body starts responding.

The main control of the thermoregulatory remains with anterior /posterior hypothalamus

The biochemical control of thermoregulation is with the endorphins (brain opioids). Injecting

endorphins directly into the hypothalamus leads to an immediate action of lowering the body

temperature. Naloxone (antagonist of opiates) block this endorphin induced lowering of temperature.

WHY? - Because that pain and temperaturesensory systems are related.

What happens in fever?

What is Fever? Bacteria or virus produce pyrogens which affect the hypothalamic set point of 98.40 F.

Temperature rises above the set point of 98.40 (370 C) high temperature damage body cells need to

lower temperature inside. Rise in the hypothalamic set point sends out signals to heat up the body:

Under the Normal conditions, the hypothalamic set point is at 98.40 and the body is also at 98.40 and

these both work to maintain the same. In fever the temperature regulating systems (anterior

hypothalamus and the preoptic area) bring about changes in the hypothalamic set point. These changes

are in response to the attack from pyrogens (form bacteria). Thus, the set point moves up to 1010 F,

whereas the body is still functioning at 98.40 F. Urgently signals are sent to the body that there is need

to heat up to meet hypothalamic set point, to preserve heat. Thus, there is a response of heat

conservation and generation i.e. shivering, cold hands and feet (circulation to the center) and faster

metabolism.

What happens when we take aspirin (antipyretic), it reduces the set point back to normal 98.40 F,

whereas now the body has been working at 1010 F. The signals this time are the body needs cooling! So,

this is why we see sweating and taking off blankets etc when the fever "breaks". The signals are to slow

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metabolism, and to radiate heat by evaporation (sweating)

In human, clothes are the thermoregulatory devices and the kinds of houses built for the climate we live

in is a thermoregulatory behavioral process as well. In animals studies have shown that they seek active

regulation of their environment i.e. rats hoard paper to warm their cages.

Thermoregulatory process is however very limited. Because freezing to death or dying from heat stroke

i.e. hypothermia or hyperthermia occur when the behavioral and physiological regulatory mechanisms

cannot cope further \

References:

1. Carlson N.R. (2005) Foundations of Physiological Psychology Allyn and Bacon, Boston

2. Pinel, John P.J. (2003) Biopsychology (5th edition) Allyn and Bacon Singapore

3. Bridgeman,B (1988)The Biology of Behavior and Mind. John Wiley and Sons New York

4. Mogensen, G.J. (1977) The Neurobiology of Behaviour: Lawrence Elbaum Associates

Note: For this chapter ref #3 and 4 have been closely followed

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