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Physiology

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Central Nervous System

Question
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Which is not occurring in child exposed to cold climate (AIIMS NOV.2011)



A Shivering

B Cutaneous vasoconstriction

C Flexion of body like fetus position

D Production of noradrenaline to release energy from brown adipose tissue

Ans. A Shivering

Temperature-Regulating Mechanisms

I. The reflex and semireflex thermoregulatory responses in humans are listed in Table 18–4.

II. They include autonomic, somatic, endocrine, and behavioral changes.

III. One group of responses increases heat loss and decreases heat production; the other decreases heat loss and increases heat production.

IV. In general, exposure to heat stimulates the former group of responses and inhibits the latter, whereas exposure to cold does the opposite.

Table 18–4 Temperature-Regulating Mechanisms.

Mechanisms activated by cold

Shivering

Hunger

Increased voluntary activity

Increased secretion of norepinephrine and epinephrine

Decreased heat loss

Cutaneous vasoconstriction

Curling up

Horripilation

Mechanisms activated by heat

Increased heat loss

Cutaneous vasodilation

Sweating

Increased respiration

Decreased heat production

Anorexia

Apathy and inertia

a. Curling up "in a ball" is a common reaction to cold in animals and has a counterpart in the position some people assume on climbing into a cold bed. Curling up decreases the body surface exposed to the environment.

b. Shivering is an involuntary response of the skeletal muscles, but cold also causes a semiconscious general increase in motor activity.

c. Increased catecholamine secretion is an important endocrine response to cold. Mice unable to make norepinephrine and epinephrine because their dopamine β-hydroxylase gene is knocked out do not tolerate cold; they have deficient vasoconstriction and are unable to increase thermogenesis in brown adipose tissue through UCP 1.

d. TSH secretion is increased by cold and decreased by heat in laboratory animals, but the change in TSH secretion produced by cold in adult humans is small and of questionable significance

e. Thermoregulatory adjustments involve local responses as well as more general reflex responses.

f. When cutaneous blood vessels are cooled they become more sensitive to catecholamines and the arterioles and venules constrict. This local effect of cold directs blood away from the skin.

g. In new born and children immature temperature regulating mechanism and Shivering is absent among newborns

h. The main mechanism of heat production is through increased noradrenaline to release energy from brown adipose tissue

Central Nervous System Flashcard List

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