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
CHAPTER TWO The Brain The brain manages all the information necessary for running the body It acts like a personal supercomputer to store and bring up thoughts feelings emotions behavior perception and memories The brain also receives information about what the body is doing and what is happening to it It processes this information and stores it until needed However the brain is better than a computer at managing peoples daily life activities The nervous system runs the body All the parts work together to send connect and receive signals over the network of neurons Living takes constant information and that takes a brain 8
Meninges A hard bony skull is the outer layer of the brain’s protective layers Skull Cerebral spinal fluid CFS Spinal cord The soft brain needs protection Three strong membranes called meninges cover the brain Fluid called cerebral spinal fluid or CFS fills the spaces between the layers It cushions and protects the brain CFS also carries hormones or special body chemicals around the brain and moves wastes to the blood Neurons carry messages and connections made in the brain Myelin an insulating cover wraps around axons of many neurons Myelin moves the messages faster The impulses jump across the axon instead of traveling along its entire length Nerve Impulse Myelin Myelin Sheath 9
