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Brain and Motivational States:Homeostasis, Temperature Regulation, Ectotherms

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Neurological Basis of Behavior (PSY - 610)
VU
Lesson37
Brain and Motivational States
Objectives:
To familiarize the students with the
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Process of homeostasis, the biological systems,
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The brain modulation of these systems
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And how the body's systems can compete with each other for the survival of the organism.
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Brain and motivational states
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Homeostasis, include temperature regulation, Hunger, thirst, bio-rhythms, Sleep and awakening.
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Pathology related to sleep cycles
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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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Neurological Basis of Behavior (PSY - 610)
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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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Neurological Basis of Behavior (PSY - 610)
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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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Neurological Basis of Behavior (PSY - 610)
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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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Table of Contents:
  1. INTRODUCTION:Descriptive, Experimental and/ or Natural Studies
  2. BRIEF HISTORICAL REVIEW:Roots of Behavioural Neurosciences
  3. SUB-SPECIALIZATIONS WITHIN THE BEHAVIORAL NEUROSCIENCES
  4. RESEARCH IN BEHAVIOURAL NEUROSCIENCES:Animal Subjects, Experimental Method
  5. EVOLUTIONARY AND GENETIC BASIS OF BEHAVIOUR:Species specific
  6. EVOLUTIONARY AND GENETIC BASIS OF BEHAVIOUR:Decent With Modification
  7. EVOLUTIONARY AND GENETIC BASIS OF BEHAVIOUR:Stereoscopic vision
  8. GENES AND EXPERIENCE:Fixed Pattern, Proteins, Genotype, Phenotypic
  9. GENES AND EXPERIENCE:Mendelian Genetics, DNA, Sex Influenced Traits
  10. GENES AND EXPERIENCE:Genetic Basis of behavior, In breeding
  11. GENES AND EXPERIENCE:Hybrid vigor, Chromosomal Abnormalities
  12. GENES AND EXPERIENCE:Behavioral Characteristics, Alcoholism
  13. RESEARCH METHODS AND TECHNIQUES OF ASSESSMENT OF BRAIN FUNCTION
  14. RESEARCH METHODS AND TECHNIQUES OF ASSESSMENT OF BRAIN FUNCTION:Activating brain
  15. RESEARCH METHODS AND TECHNIQUES OF ASSESSMENT OF BRAIN FUNCTION:Macro electrodes
  16. RESEARCH METHODS AND TECHNIQUES OF ASSESSMENT OF BRAIN FUNCTION:Water Mazes.
  17. DEVELOPMENT OF THE NERVOUS SYSTEM:Operation Head Start
  18. DEVELOPMENT OF THE NERVOUS SYSTEM:Teratology studies, Aristotle
  19. DEVELOPMENT OF THE NERVOUS SYSTEM:Stages of development, Neurulation
  20. DEVELOPMENT OF THE NERVOUS SYSTEM:Cell competition, Synaptic Rearrangement
  21. DEVELOPMENT OF THE NERVOUS SYSTEM:The issues still remain
  22. DEVELOPMENT OF THE NERVOUS SYSTEM:Post natal
  23. DEVELOPMENT OF THE NERVOUS SYSTEM:Oxygen level
  24. Basic Neuroanatomy:Brain and spinal cord, Glial cells, Oligodendrocytes
  25. Basic Neuroanatomy:Neuron Structure, Cell Soma, Cytoplasm, Nucleolus
  26. Basic Neuroanatomy:Control of molecules, Electrical charges, Proximal-distal
  27. Basic Neuroanatomy:Telencephalon, Mesencephalon. Myelencephalon
  28. Basic Neuroanatomy:Tegmentum, Substantia Nigra, MID BRAIN areas
  29. Basic Neuroanatomy:Diencephalon, Hypothalmus, Telencephalon, Frontal Lobe
  30. Basic Neurochemistry:Neurochemicals, Neuromodulator, Synaptic cleft
  31. Basic Neurochemistry:Changes in ionic gates, The direct method, Methods of Locating NT
  32. Basic Neurochemistry:Major Neurotransmitters, Mesolimbic, Metabolic degradation
  33. Basic Neurochemistry:Norepinephrine/ Noradrenaline, NA synthesis, Noadrenergic Pathways
  34. Basic Neurochemistry:NA and Feeding, NE and self stimulation: ICS
  35. Basic Neurochemistry:5HT and Behaviors, Serotonin and sleep, Other behaviours
  36. Basic Neurochemistry:ACH and Behaviors, Arousal, Drinking, Sham rage and attack
  37. Brain and Motivational States:Homeostasis, Temperature Regulation, Ectotherms
  38. Brain and Motivational States:Biological Rhythms, Circadian rhythms, Hunger/Feeding
  39. Brain and Motivational States:Gastric factors, Lipostatic theory, Neural Control of feeding
  40. Brain and Motivational States:Resting metabolic state, Individual differences
  41. Brain and Motivational States:Sleep and Dreams, Characteristics of sleep
  42. Higher Order Brain functions:Brain correlates, Language, Speech Comprehension
  43. Higher Order Brain functions:Aphasia and Dyslexia, Aphasias related to speech
  44. Higher Order Brain Functions:Principle of Mass Action, Long-term memory
  45. Higher Order Brain Functions:Brain correlates, Handedness, Frontal lobe