9781422280386

The Brain and Nervous System

can’t do its job without help. That’s where the peripheral nervous system (PNS) comes in. The PNS gathers data from the senses and from all over the body via your nerves and ganglia . It sends that data to the CNS. The CNS decides how to respond, and sends messages back to the PNS directing the body to take one or more actions. If you’re walking in the woods and see a bear, your nervous system sends data from your eyes to your brain. Your brain processes that information and sends back immediate responses. It may direct your leg muscles to run away as fast as you can. The PNS makes those leg muscles move. But the brain is the part that recognizes a bear and decides that you are in danger. The Great Brain The brain sits at the top and back of your head, protected by your hair, the skin of your scalp, and your bony skull. Inside the skull, the brain is further protected by three layers of membranes called the meninges . Squeezed into this protected space, the brain contains an estimated 100 billion special cells called neurons . Neurons communicate with one another via pathways throughout the brain. They communicate with other types of cells throughout the body via the spinal cord and the peripheral nervous system. Neurons are not the only type of cells in the brain, but the work they do is what puts the brain in charge. The brain is organized into three different sections: the forebrain, the midbrain, and the hindbrain. The hindbrain manages physical activities that you do without thinking; it makes your heart beat regularly, for example, and your lungs breathe in and out. The hindbrain also contains the cerebellum , which manages some types of movement. If you hit a baseball for a home run—or swing and miss for the out—your cerebellum was calling the shots. Located deep inside the brain, the midbrain is responsible for routing messages to and from the brain to the rest of the body via the spinal cord.

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