Tissue damage activates nociceptors or pain receptors in the skin. A signal is sent to the peripheral nerve to the spinal cord where neurotransmitters or chemical messengers are released. It activates other nerves to pass signal to the brain. The signals are relayed to the somatosensory cortex for sensation, frontal cortex for thinking and limbic system for emotional response.
Explanation: The energy pyramid describes how energy gets distributed through an ecosystem. The more there is of an organism on the energy pyramid, the more it gives overall to the ecosystem. The less there is of an organism, the less it gives to the ecosystem. Take the Floridian Everglades as an example. There is an abundance of sawgrass, and that makes up the foundation of the system, along with mangroves and such. But there are less of predators in the ecosystem because they only feed of of their prey like small mammals or fish. They never start the food chain, they end it.
Populations tend to grow because of repopulation.