Neuronal control

Neuronal control

The graphic of the neuronal control of temperature regulation is divided into two parts: the reaction of the body to cold situations at the left and the adjustment to warm situations at the right.

Reaction to cold:

When cold sensors (cold receptors) measure a decrease in temperature, they will increase the frequency of action potentials transmitting to the hypothalamus (the heat sensors become silent). The coordinating centre in the anterior hypothalamus notifies that the body temperature has dropped in comparison to the thermostat set point. The anterior hypothalamus will then send information to the posterior centres in order to activate the heat-gain processes. The posterior hypothalamus regulates heat gain by 3 main pathways. The hypothalamus activates γ-motor neurons in order to stimulate muscle tissues. This results in an increase in the muscle tone. When this tone goes above a certain threshold, muscles will contract in an irregular way (shivering). This process is controlled by the primary motor centre for shivering and produces relatively much heat. The adrenergic part of the sympathetic nervous system is activated. The metabolism of the brown fat is increased (young children) and the blood vessels in the periphery (skin) are constricted. The latter event reduces the heat loss via the skin. And piloerection occurs for better isolation (this is more important in mammals then in humans). The cerebral cortex is informed about the dropping temperature. This means that the cold

is translated to "feeling chilly" and thus experienced as cold. The individual will consciously adjust his behaviour to reduce heat loss and to increase heat production: e.g. he will put the heating on, get warmer clothes, and increase muscle activities. This behavioural adjustment is of great importance at low temperatures. Reaction to heat:

When heat sensors (warm receptors) measure an increase in temperature, they will increase the frequency of action potentials transmitting to the hypothalamus (the cold sensors become silent). The coordinating centre in the posterior hypothalamus notifies that the body temperature has increased in comparison to the thermostat set point and will then send action potentials in order to activate the heat-loss processes. The posterior hypothalamus regulates heat loss by 3 main pathways. The hypothalamus inhibits γ-motor neurons in order to decrease the muscle tone and to inhibit muscle activities. The cholinergic part of the sympathetic nervous system is activated. The blood vessels in the periphery (skin) are dilated in order to enhance heat loss via the skin. Furthermore, the sweat glands are stimulated. This enhances heat loss by evaporation. The cerebral cortex is informed about the increasing temperature. This means that the heat is translated to "feeling warm" and thus experienced as warm. The individual will consciously adjust his behaviour to reduce heat production and to increase cooling: e.g. he will take of clothes, and decrease activities.

1

Perspiration is more effective when the environment is humid. 

2

When the temperature in the anterior hypothalamus exceeds the thermostat setpoint, the heat-gain centre is stimulated. 

3

Vasodilatation of blood vessels in the skin results in a reddish color.