Overview
This section explains the main divisions of the nervous system, focusing on the distinctions and functions of the central and peripheral systems, especially the somatic and autonomic nervous systems.
Major Divisions of the Nervous System
- The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
- The CNS consists of the brain and spinal cord.
- The PNS connects the CNS to the rest of the body, including muscles, organs, and senses.
Peripheral Nervous System (PNS)
- The PNS is composed of nerves, which are bundles of axons carrying information to and from the CNS.
- The PNS is subdivided into the somatic nervous system and the autonomic nervous system.
Somatic Nervous System
- Controls conscious or voluntary activities by transmitting sensory and motor information.
- Consists of motor neurons (efferent, carrying signals away from the CNS) and sensory neurons (afferent, carrying signals toward the CNS).
- Nerves contain both efferent and afferent fibers, enabling two-way communication.
Autonomic Nervous System
- Regulates involuntary functions of internal organs and glands.
- Divided into the sympathetic and parasympathetic nervous systems.
- The sympathetic division prepares the body for stress or high-arousal situations (fight or flight response).
- The parasympathetic division calms the body, returning it to routine operations and maintaining homeostasis (balance).
Sympathetic vs. Parasympathetic Divisions
- Sympathetic activation dilates pupils, increases heart rate, relaxes the bladder, and releases adrenaline.
- Parasympathetic activation constricts pupils, slows the heart rate, stimulates digestion, and restores bladder control.
- Both systems work together to maintain homeostasis.
Stress Response and Health
- The fight or flight response is adaptive for physical threats but can harm health when triggered by psychological stress.
- Chronic stress related to repeated sympathetic activation can increase risks for heart disease and weaken the immune system.
- The parasympathetic system restores the body to a restful state after the threat passes.
Key Terms & Definitions
- Central Nervous System (CNS) — brain and spinal cord.
- Peripheral Nervous System (PNS) — nerves outside the CNS connecting it to the body.
- Somatic Nervous System — voluntary movement and sensory information relay system.
- Autonomic Nervous System — controls involuntary internal organ functions.
- Sympathetic Nervous System — manages the fight or flight response.
- Parasympathetic Nervous System — returns the body to a calm state after stress.
- Efferent Fibers — nerve fibers that carry signals away from the CNS.
- Afferent Fibers — nerve fibers that carry signals toward the CNS.
- Homeostasis — state of internal balance in biological conditions.
Action Items / Next Steps
- Watch the linked video on the Fight-Flight-Freeze response for further understanding.
- Review the next section on the brain and spinal cord for deeper insight.