Brain and Nerves

The brain and nerves form the body’s fast communication network. They help you think, feel, move, sense the world, react to danger and control many body functions automatically.

The nervous system is the body’s rapid messaging and control system. It includes the brain, spinal cord and nerves. The brain is the main control centre. It helps with thinking, memory, emotion, movement, speech, decision making, balance, sensation and automatic body functions. It is not just one simple control box. Different areas of the brain are involved in different tasks, but they work together as networks. The spinal cord is a major pathway running from the brain down through the spine. It carries messages between the brain and the rest of the body. It also helps coordinate some fast responses called reflexes, e.g., pulling your hand from a hot stove, without you having to think about them first. Nerves are like communication cables. Each one is made up of many individual neurons, cells that carry electrical signals rapidly along their length. Together, nerves carry these signals between the brain, spinal cord, muscles, skin and organs. Some nerves carry information from the body to the brain. Others carry instructions from the brain or spinal cord to the body. The nervous system can be divided in different ways. The central nervous system includes the brain and spinal cord. The peripheral nervous system includes nerves outside the brain and spinal cord. Some nerve activity is voluntary. For example, choosing to lift your hand involves signals travelling from the brain through nerves to muscles. Other nerve activity is automatic. Your nervous system helps adjust heart rate, breathing, digestion, sweating, pupil size and many other functions without you consciously controlling each one. The nervous system also helps with sensation. Receptors in the skin, muscles, joints, eyes, ears and other parts of the body collect information. Nerves carry this information toward the brain, where it can be interpreted. The brain and nerves work closely with other systems. The muscles need nerve signals to move. The heart and lungs receive automatic signals. Hormones can influence mood, energy and stress responses. The immune system can affect how the body and brain respond during illness. What a doctor checks when examining the nervous system A doctor cannot see nerve signals directly, but a structured examination reveals a great deal about how the nervous system is working. Consciousness and general observation. A doctor first notes whether someone is fully alert, drowsy, or confused, since this reflects how the brain as a whole is functioning. Pupils and facial symmetry. Shining a light into each eye and watching the pupils narrow shows whether specific nerve pathways between the eye and brain are intact. Checking facial symmetry, by asking someone to smile or raise their eyebrows, reveals whether the nerves controlling facial muscles are working evenly on both sides. Power. A doctor asks someone to push or pull against resistance in the arms and legs, comparing one side with the other, to check whether muscles are receiving normal nerve signals. Sensation. Light touch and pinprick are tested at different points on the skin to check whether sensory nerves are carrying information normally toward the brain. Reflexes. Tapping a tendon, such as just below the kneecap, triggers a fast, automatic muscle response coordinated by the spinal cord. A reflex that is too strong, too weak, or absent can point to where in the nervous system a problem sits. Coordination and speech. Asking someone to touch their nose then the doctor's finger, or to walk in a straight line, tests how well different parts of the nervous system work together. Listening to speech for clarity and fluency adds another layer of information. Symptoms and what they represent A headache, dizziness, weakness, numbness, or sudden confusion each point toward a different part of the nervous system, or a different way it can be disrupted. A headache often reflects irritation or pressure affecting pain sensitive structures in or around the brain, rather than the brain tissue itself, which has no pain receptors of its own. Dizziness can mean the balance sensing pathways between the inner ear and brain are affected, or that blood flow to the brain has briefly changed. Weakness on one side of the body suggests a problem somewhere along the pathway carrying movement signals from the brain to the muscles. Numbness suggests the same for the pathway carrying sensation in the opposite direction. Sudden confusion suggests the brain's own processing has been disrupted, which doctors treat as needing urgent assessment. Recognising which part of the nervous system a symptom points toward is the first step in understanding a doctor's approach. It explains why they ask specific questions and run specific checks.

The nervous system is the body’s fast communication network: the brain processes information, the spinal cord carries messages, and nerves connect the body.