<P> The nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body . The nervous system detects environmental changes that impact the body , then works in tandem with the endocrine system to respond to such events . Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago . In vertebrates it consists of two main parts , the central nervous system ( CNS ) and the peripheral nervous system ( PNS ) . The CNS consists of the brain and spinal cord . The PNS consists mainly of nerves , which are enclosed bundles of the long fibers or axons , that connect the CNS to every other part of the body . Nerves that transmit signals from the brain are called motor or efferent nerves , while those nerves that transmit information from the body to the CNS are called sensory or afferent . Spinal nerves serve both functions and are called mixed nerves . The PNS is divided into three separate subsystems , the somatic , autonomic , and enteric nervous systems . Somatic nerves mediate voluntary movement . The autonomic nervous system is further subdivided into the sympathetic and the parasympathetic nervous systems . The sympathetic nervous system is activated in cases of emergencies to mobilize energy , while the parasympathetic nervous system is activated when organisms are in a relaxed state . The enteric nervous system functions to control the gastrointestinal system . Both autonomic and enteric nervous systems function involuntarily . Nerves that exit from the cranium are called cranial nerves while those exiting from the spinal cord are called spinal nerves . </P>
<P> The nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body . The nervous system detects environmental changes that impact the body , then works in tandem with the endocrine system to respond to such events . Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago . In vertebrates it consists of two main parts , the central nervous system ( CNS ) and the peripheral nervous system ( PNS ) . The CNS consists of the brain and spinal cord . The PNS consists mainly of nerves , which are enclosed bundles of the long fibers or axons , that connect the CNS to every other part of the body . Nerves that transmit signals from the brain are called motor or efferent nerves , while those nerves that transmit information from the body to the CNS are called sensory or afferent . Spinal nerves serve both functions and are called mixed nerves . The PNS is divided into three separate subsystems , the somatic , autonomic , and enteric nervous systems . Somatic nerves mediate voluntary movement . The autonomic nervous system is further subdivided into the sympathetic and the parasympathetic nervous systems . The sympathetic nervous system is activated in cases of emergencies to mobilize energy , while the parasympathetic nervous system is activated when organisms are in a relaxed state . The enteric nervous system functions to control the gastrointestinal system . Both autonomic and enteric nervous systems function involuntarily . Nerves that exit from the cranium are called cranial nerves while those exiting from the spinal cord are called spinal nerves . </P>
how many types of nervous systems are there
how many types of nervous systems are there
two
two