Autonomic nervous system: Parts, organization and functions
Major Organs and Divisions of the Nervous System
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The nervous system is anatomically and functionally partitioned into the central nervous system and peripheral nervous system.
- Making up the central nervous system (CNS) are the
brain and
spinal cord, which serve as the body’s assessment and control center.
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- These vital organs are surrounded and protected by the bones of the skull and vertebral column.
- The peripheral nervous system (PNS) is formed by a network of
nerves that extend throughout the body.
- The nerves connect to the central nervous system via 12 pairs of
cranial nerves and 31 pairs of
spinal nerves.
- Inside the nerves are the
axon processes of numerous nerves cells (or neurons).
- The wire-like axons run the length of the nerves and are grouped by connective tissue into cylindrical bundles called
fascicles (L. fasciculi).
-
Sensory neuron axons conduct impulses from the peripheral organs to the CNS.
-
Motor neuron axons conduct impulses from the CNS to the peripheral organs.
- Most nerves are
mixed, meaning they contain both motor and sensory neurons.
- Based on their functions, the neurons in nerves divide the peripheral nervous system into somatic and autonomic nervous systems.
- Somatic neurons carry signals that allow the CNS to consciously monitor the external environment and control body movements. In contrast, autonomic neurons carry signals that allow the CNS to subconsciously regulate the body’s internal environment and control the activity of the soft organs (viscera).
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General Organization of the Nervous System