CHAPTER ONE Parts of the Nervous System Hop on a skateboard and push off Eyes arms legs and muscles must coordinate to stay balanced and keep moving How is this possible Humans have a complex command center to run the body called the nervous system The brain spinal cord and nerves form the nervous system This system receives interprets and relays information to manage and direct everything happening in the body Electrical signals called impulses carry information They move from the body to the brain and back again Did You Know Living organisms develop in an ordered way The smallest unit of life is a cell Like cells doing the same job form tissues Tissues working together make an organ Organs working together on the same process create a system All the different systems working together make an organism 4
The nervous system is divided into two parts The brain and spinal cord make up the central nervous system CNS The peripheral nervous system PNS is all the nerves outside the brain and spinal cord The nerves of the PNS connect the sense organs and other body activities to the CNS Messages move through neurons or nerve cells Bodies hold around 100 billion neurons Another 100 billion neurons make up the brain The impulses from these cells move in different directions to carry their messages Bundles of neurons form nerves Central Nervous System Brain Spinal Cord Peripheral Nervous System Motor Nerves Nerve Neuron Bundle Sensory Nerves Blood Vessel Axion Connective Tissue 5
Two kinds of neurons send messages Sensory neurons carry messages from the senses to the brain and back Motor neurons carry messages from the brain to muscle fibers and back A third kind of neuron is association neurons They communicate with other neurons in the brain and spinal cord They let people think remember and understand their surroundings The brain is constantly managing directing or storing the incoming and outgoing information A neuron ends with branched strands called dendrites The dendrites receive signals from other neurons and relay them to the cell body The nucleus in the cell body is like a miniature brain It directs cell actions Nerve Cell Cell Body 6 Dendrite Axon Terminal Nucleus Axon Myelin Sheath
Dendrites almost touching at the synapse The spinal cord extends from the brain down through the backbone It connects the brain to the body’s sensory neurons The spinal cord helps the brain process information and passes it on to the muscles The axon also holds branched endings It transmits signals away from the neuron Neurons don’t touch A tiny gap called a synapse keeps them from touching like the spaces along a sidewalk Chemicals send the impulse across the synapse to the dendrites of the next neuron much like a spark from static electricity shoots from a hand to a doorknob before touching it The leftover chemicals reabsorb after the message is sent 7
