1

THALAMUS & HYPOTHALAMUSLecture – 10Dr. Zahoor Ali Shaikh

2

THALAMUS & HYPOTHALAMUS•Thalamus and Hypothalamus are called

DIENCEPHALON.Why ?•Because it means mid-line structure. •Thalamus lies between cerebral cortex

and midbrain.•Thalamus is mass of nerve cells.

3

4

5

THALAMUSWhat is the function of Thalamus ?•It is relay station for processing of

sensory input Somatic, auditory, visual , visceral

( except olfactory ).•All sensory input synapses in the

thalamus on its way to the cortex.•Plays role in sleep- awake cycle

6

THALAMUS

•Thalamus is capable of awareness of sensation e.g. pain but lacks the sense of localization or intensity.

•(Localization and intensity analysis is the function of sensory cortex).

•Thalamus also plays role in motor control by re-enforcing voluntary motor behavior initiated by the cortex.

7

HYPOTHALAMUS

•Hypothalamus is collection of nuclei and associated fibers that lie beneath the thalamus.

•It is integrating center for many functions and control center for autonomic nervous system (ANS).

8

FUNCTIONS OF HYPOTHALAMUS (cont)• Functions are 1. Controls body temperature 2. Controls thirst and urine output 3. Controls food intake(Hunger and Satiety center

) 4. Controls anterior pituitary hormone secretion 5. Produces posterior pituitary hormones 6. Controls uterine contraction and milk ejection 7. Serves as major ANS coordinating center 8. Plays role in emotional and behavioral pattern 9. Participates in the sleep – wake cycle

9

HYPOTHALAMUS

•We will discuss Body Temperature Regulation

•Normal Body Temperature oral – 98.4oF (37oC)

•Normal range 97 to 99oF (36 to 37.5oC)•Axillary temperature (under the armpit) is

same as oral temperature (98.4oF)•Rectal temperature is 1oF higher

10

HYPOTHALAMUS

•Recent device – temporal scanner – it measures the temperature of blood in the temporal artery (heat radiating from the body).

•Method – computerized instruments is put across the forehead over the temporal artery which lies less than 2mm below the skin surface in this region.

11

12

HYPOTHALAMUS• Core temperature - It is temperature of deep tissues of the body (the

core of the body). - It remains constant within ±1oF .

• Skin temperature- It rises and falls with the surrounding temperature.

Important - Fat of subcutaneous tissue in the body works as insulator (less

heat loss)- In female, fat insulation is better.

13

TEMPERATURE REGULATIONWhy there is body temperature, how it is

produced ?•Heat production depends on oxidation of

metabolic fuel derived from food.• Temperature varies from organ to organ.•Body temperature within the inner core

i.e. abdominal, thoracic organs, CNS and skeletal muscle generally remains constant.

14

TEMPERATURE REGULATION

Important • If internal body temperature rises to

106oF (41oC), people get convulsions.•Temperature of 110oF (43.3oC) is upper

limit which is compatible with life.

15

TEMPERATURE REGULATION

Normal variation in core temperature•Normal temperature is 98.4oF but can

vary by 1.8oF during the day, lowest level in the morning 6-7am and highest point in the afternoon 5-7pm.

•Women have temperature change with menstrual cycle, temperature is 0.9oF (0.5oC) higher during the last half of the menstrual cycle due to ovulation.

16

TEMPERATURE REGULATION

Normal variation in core temperature•Core temperature increases during the

exercise.•Old people have lower temperature (older is

colder).•Effect of extreme hot and cold on core

temperature is little due to regulatory mechanism of hypothalamus.

•Hypothalamus balances heat input and heat output to keep core temperature stable.

17

TEMPERATURE REGULATION•Heat gain and heat loss can be adjusted by

the body to maintain the body temperature.•Heat exchange takes place by - Radiation - Conduction - Convection - Evaporation•Heat loss or gain occurs between body and

surrounding, down the thermal gradient i.e. from warmer to a cooler region.

18

TEMPERATURE REGULATIONWe will study 1. Radiation•It is loss of heat by heat waves or

electromagnetic waves which travel through space.

•Human body loses heat to surrounding and absorbs heat from the sun.

•Body loses half of the heat through radiation.

19

TEMPERATURE REGULATION

2. Conduction•Heat loss occurs by direct contact, heat

moving down the thermal gradient (from warmer to cooler).

•Small percentage of heat exchange occurs between skin and environment by conduction.

20

TEMPERATURE REGULATION

3. Convection•It is loss of heat by air currents.•Warm air rises from surface of body while

cooler air moves into the skin in place of warm air e.g. fan or wind.

21

TEMPERATURE REGULATION

4. Evaporation•Heat loss from the skin surface, it is to

transform water to gaseous state e.g. heat loss from wet bathing suit.

•Heat loss by evaporation occurs from the respiratory airways.

22

Mechanism of

Heat Transfer

23

TEMPERATURE REGULATIONSweating• It is active form of heat loss.•Sweating is under control of sympathetic ANS.•When surrounding temperature exceeds the

skin temperature, we lose heat by sweating.•At normal temperature, 100ml of sweat is

produced per day but sweating increases to 1.5 liters during hot weather.

•During heavy exercise, sweating can be up to 4 liters.

24

TEMPERATURE REGULATIONWhat is Sweat ?•It is dilute salt solution given out by sweat

glands.

Why odor in the sweat ?•Sweat glands in the armpit, produce thick

sweat rich in protein and lipids, when bacteria in the vicinity act on these rich organic constituents, odor is produced.

25

TEMPERATURE REGULATION

Sweat (cont)•If there is humidity in the air i.e. water

vapor, sweat can not evaporate, therefore remains on the body surface and drips off instead of evaporating.

•Therefore, combined increased temperature and humidity causes discomfort.

26

TEMPERATURE REGULATION

Role of Hypothalamus•Hypothalamus is body’s thermostat i.e.

regulates the body temperature.•Hypothalamus receives afferent

information about core and skin temperature from different regions of body through receptors called thermoreceptors.

27

TEMPERATURE REGULATION

•In hypothalamus, there are two centers for temperature regulation:

1. Posterior region of hypothalamus (activated by cold) – it causes heat production and heat conservation.

2. Anterior region of hypothalamus (activated by warmth) – it causes heat loss.

28

TEMPERATURE REGULATIONHeat Production (Posterior Hypothalamus)• In response to cold, heat is produced by i) Shivering – it consists of rhythmic,

oscillating skeletal muscle contraction at the rate of 10-20/sec. It is very effective in heat production. Internal heat production increases 2-5 fold in seconds to minutes.

ii) Decrease heat loss by skin vasoconstriction

29

TEMPERATURE REGULATION

iii) Behavioral adaptation e.g. postural changes, hand rubbing (hypothalamus influences the behavioral responses)

iv) Putting warm clothes – it insulates the body from too much heat loss

30

TEMPERATURE REGULATION

Heat Loss (Anterior Hypothalamus)•In response to warm surrounding, heat

loss occurs i) By vasodilatation – it permits increase

flow of blood through the skin and increase heat loss

Skin vaso-motor responses are co-ordinated by hypothalamus through sympathetic ANS

ii) Sweating

31

TEMPERATURE REGULATION

iii) Reduced heat production by decreasing skeletal muscle activity

iv) Using fan, wearing cool clothing, drinking cold beverages

32

Thermoregulatory pathways

33

34

ABNORMALITIES OF BODY TEMPERATURE REGULATIONFever • It means body temperature above the

usual normal range.•It can be caused by toxic substances that

affect temperature regulating centers, brain lesions, heat stroke.

•Increase body temperature occurs in infection or inflammation.

35

ABNORMALITIES OF BODY TEMPERATURE REGULATION•In bacterial infection, macrophage release

endogenous pyrogen which act on hypothalamic thermo-regulatory center to raise the thermostat at higher temperature e.g. 102oF.

•Hyperthermia can be induced by exercise.•Hyperthermia can be due to increased

level of thyroid hormone or epinephrine.

36

HEAT EXHAUSTION

•Heat Exhaustion occurs when people are exposed to high temperature combined with increased physical activity and humidity.

•Body fluids are lost through sweating causing dehydration and over-heating of the body.

•Person’s temperature increases mild to moderate, up to 104oF (40oC).

•It can cause collapse, fainting, decreased blood pressure.

37

HEAT STROKE

•It is very dangerous, occurs due to breakdown of thermo-regulatory mechanism in hypothalamus.

•It occurs due to prolonged exposure to hot, humid environment.

•Heat loss, thermo-regulatory mechanism are not working, therefore, no sweating occurs and there is rapid rise in body temperature.

38

HEAT STROKE

•Internal body temperature rises and brain damage or damage to other internal organ may result.

•Temperature may reach 105oF (40.5oC) or more.

•In heat stroke, convulsion, confusion may occur.

39

Steps to reduce the risk of Heat Exhaustion and Heat Stroke

•Stay out of sun during hottest part of the day.

•Avoid extreme physical exertion.•Give plenty of cold drink.•Take cool shower, bath or body wash.•Keep the environment cool.

40

COLD RELATED DIS-ORDER

Frost bite•There is excessive cooling of particular

part of the body to the point where tissue in that area is damaged.

Hypothermia•Fall in body temperature occurs when

generalized cooling of the body occurs.•It can cause loss of judgment,

disorientation.

41

COLD RELATED DIS-ORDER

•Exposure to ice-water for 20-30mins can cause death due to ventricular fibrillation or heart stops as body temperature falls to 77oF (25c).

•Loss of temperature regulation occurs when temperature goes below 85oF ( 30 c)

42

Thank you