![]() ![]() The enteric nervous system functions to control the gastrointestinal system. 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 autonomic nervous system is further subdivided into the sympathetic and the parasympathetic nervous systems. ![]() Somatic nerves mediate voluntary movement. The PNS is divided into three separate subsystems, the somatic, autonomic, and enteric nervous systems. Spinal nerves are mixed nerves that serve both functions. Nerves that transmit signals from the brain are called motor nerves or efferent nerves, while those nerves that transmit information from the body to the CNS are called sensory nerves or afferent. 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. The CNS consists of the brain and spinal cord. In vertebrates it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). ![]() Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago. The nervous system detects environmental changes that impact the body, then works in tandem with the endocrine system to respond to such events. In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. ![]()
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