THALAMUS & HYPOTHALAMUS Lecture – 2 Dr. Zahoor Ali Shaikh

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.

THALAMUS What 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

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.

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).

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

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 (0.6oC) higher

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.

TEMPORAL SCANNER INFRARED THERMOMETER

HYPOTHALAMUS Core temperature - It is temperature of deep tissues of the body (the core of the body). - It remains constant within ±1oF (0.6oC) 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.

TEMPERATURE REGULATION Why 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.

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.

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.

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.

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.

TEMPERATURE REGULATION We 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.

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.

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.

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.

Mechanism of Heat Transfer

TEMPERATURE REGULATION Sweating 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.

TEMPERATURE REGULATION What 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.

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.

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.

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.

TEMPERATURE REGULATION Heat 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

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

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

TEMPERATURE REGULATION iii) Reduced heat production by decreasing skeletal muscle activity iv) Using fan, wearing cool clothing, drinking cold beverages

Thermoregulatory pathways

ABNORMALITIES OF BODY TEMPERATURE REGULATION Fever 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.

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.

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.

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.

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.

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.

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.

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. Loss of temperature regulation occurs when temperature goes below 85oF. Artificial hypothermia – temperature is maintained below 90oF, this temperature doesn’t cause tissue damage, but decreases heart rate and metabolism.

Thank you