The Nervous System

Core concept

For example, touching a hot object triggers a reflex arc: a receptor in the skin detects heat, sending a signal through a sensory neuron to the spinal cord, which immediately sends a signal through a motor neuron to the arm muscles, causing withdrawal — all before the brain has even fully processed the sensation of pain, protecting the body from prolonged injury. The brain itself has specialised regions: the cerebrum controls voluntary actions and thought, the cerebellum coordinates balance and muscle coordination, and the medulla oblongata controls involuntary functions like breathing and heart rate.