Millions of nerve and glial cells. Brain and spinal cord.
types of neurons nerve cells the human body is made up of trillions of cells cells of the nervous system called nerve cells or neurons are specialized to carry messages through an electrochemical process the human brain has approximately 100 billion neurons to learn how neurons carry messages read about the action potential some differences between the peripheral nervous system pns and the central nervous system cns in the cns collections of neurons are called nuclei in the pns collections of neurons are called ganglia in the cns collections of axons are called tracts in the pns collections of axons are called nerves  2 the structures that form the nervous system can be divided into the central nervous system cns and the peripheral nervous system pns the organs of the cns are the brain cerebrum brainstem and cerebellum and spinal cord the pns is made of nerves and neural ganglia in addition to these organs the meninges dura mater arachnoid and pia mater are also a part of the nervous system since they cover and protect the encephalon and the spinal cord glial cells and neurons are the cells that form the nervous system neurons are cells that have the function of receiving and transmitting neural impulses whereas glial cells astrocytes microgliacytes ependymal cells and oligodendrocytes are the cells that support feed and insulate electrically the neurons neurons nerve cells the nervous system is composed of two parts central nervous system consists of all neurons nerve cells located in the brain and spinal cord peripheral nervous system consists of all neurons nerve cells located outside the brain and spinal cord  the central nervous system cns is composed of the brain and spinal cord the peripheral nervous system pns is composed of spinal nerves that branch from the spinal cord and cranial nerves that branch from the brain  the central nervous system is composed of millions of nerve and glial cells together with blood vessels and a little connective tissue the nerve cells or neurons are characterized by many processes and are specialized for reception and transmission of signals  the central nervous system cns is composed of the brain and spinal cord the cns is surrounded by bone skull and vertebrae fluid and tissue also insulate the brain and spinal cord areas of the brain the above image is from http www prs k12 nj us schools phs science dept apbio pic brain gif the peripheral nervous system pns connects the cns to other parts of the body and is composed of nerves bundles of neurons not all animals have highly specialized nervous systems those with simple systems tend to be either small and very mobile or large and immobile all the sensory axons pass into the dorsal root ganglion where their cell bodies are located and then on into the spinal cord itself all the motor axons pass into the ventral roots before uniting with the sensory axons to form the mixed nerves it connects a large part of the peripheral nervous system to the brain information nerve impulses reaching the spinal cord through sensory neurons are transmitted up into the brain signals arising in the motor areas of the brain travel back down the cord and leave in the motor neurons  the central nervous system cns in its most simple divisions consists of all nervous tissue in the spinal cord and the brain it is the largest division of the nervous system and has primary control over all organism behavior 
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the cns is composed of