Source: # Understanding the nervous system *From the book – Chapter 3: Human Brain and Nervous System* ## The nervous system **Figure 3.3** *How the nervous system is organised.* ### Central nervous system (CNS) - Brain. - Spinal cord. - Processes and coordinates information. ### Peripheral nervous system (PNS) - Nerves throughout the body. - Carries information to and from the CNS. - Two divisions: - Somatic nervous system: voluntary movements. - Autonomic nervous system: automatic functions. In short, the central nervous system is the brain and spinal cord. Everything else is peripheral. Somatic nerves move the limbs you can point to. Autonomic nerves run the interior. ### Autonomic nervous system: two branches #### Sympathetic nervous system (fight-or-flight) - Activates during stress or danger. - Increases heart rate. - Dilates pupils. - Redirects blood to muscles. - Prepares body for action. #### Parasympathetic nervous system (rest-and-digest) - Activates during rest. - Slows heart rate. - Promotes digestion. - Supports healing and recovery. - Conserves energy. The two branches work as a balance, not a light switch. The hypothalamus sits on the border of neural and hormonal control and aims the pituitary at the rest of the endocrine system — including the HPA stress axis and cortisol. Clinic note. Anxiety often feels like a sympathetic system that will not stand down. Depression and exhaustion often feel like a system that will not stand up. 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