Nervous system

What are you doing right now? Your eyeballs are moving as you read and make sense of these words. You are breathing and your heart is pumping blood and oxygen throughout your blood vessels. You are sitting upright in your chair, contracting some muscles and relaxing others so that you don’t tumble to the floor. Can you hear anything? What kind of mood are you in?

Your nervous system is working twenty-four hours a day, seven days a week to allow you to do these marvelous tasks, from digesting your breakfast to texting a friend.

The nervous system is made up of the brain, spinal cord, and the nerves of the body (there’s a lot of them!). It is the body’s control center: it controls and responds to body functions and directs behavior. The nervous system is responsible for everything from automatic responses (such as heart rate and breathing) to sensing and perceiving (seeing, hearing, smelling, tasting, touching), to emoting, moving, thinking, and talking. The nervous system influences and is influenced by all other body systems, such as the cardiovascular, endocrine, and immune systems. Because specific parts of the brain are specialized to perform certain functions, damage to a particular area of the brain can disrupt specific activities.

The human nervous system is divided in two parts: the central nervous system (CNS) (brain and the spinal cord) and the peripheral nervous system (PNS) (the nerves extending out of and into the brain and spinal cord). The major nerves of the PNS are shown on the diagram above. The autonomic nervous system controls the internal organs.

By far the largest part is the brain with 100 billion nerve cells and weighing 1.4 kg.  The complexity of the nervous system depends on the organism.

Allen Jones A Map of the Brain

Ed Boyden: A lightswitch for neurons