Homeostasis
Homeostasis is the process by which living organisms maintain a stable internal environment despite changes in external conditions. This regulation is necessary for the proper functioning of cells and organs, ensuring that factors such as temperature, pH and fluid balance remain within narrow limits.
Negative Feedback and the Stimulus-Response Model
The nervous system plays a key role in maintaining homeostasis by using negative feedback mechanisms to detect and respond to internal and external stimuli.
When a change in the internal or external environment is detected—referred to as the stimulus—sensory receptors send signals to the brain or spinal cord, which act as control centres. The control centre processes the information and triggers an appropriate response, usually by activating effectors such as muscles or glands. This response aims to counteract the initial change, returning the system to its optimal state. Negative feedback is an important component of this process, where the response generated reduces or negates the original stimulus.
For example, if the body temperature rises above the normal range, thermoreceptors in the skin and brain detect the increase. This information is sent to the hypothalamus, which initiates responses such as sweating and vasodilation to cool the body down. Conversely, if the body temperature drops, shivering and vasoconstriction are triggered to conserve heat.