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1.2 Overview of the Nervous System

Syllabus
2025
Topic
1.2
Level
—

Learning objectives

1.2A—Differentiate among the subsystems of the human nervous system and their functionsDifferentiate among the subsystems of the human nervous system and their functions.• The central nervous system includes the brain and the spinal cord and interacts with all processes in the body.• The peripheral nervous system relays messages from the central nervous system to the rest of the body and includes the autonomic and somatic nervous systems.- i. The autonomic nervous system governs processes that are involuntary and includes the parasympathetic and sympathetic nervous systems.- ii. The somatic nervous system governs processes that are voluntary.

How the Nervous System Is Organized

The human nervous system has two main divisions. The central nervous system (CNS)—the brain and spinal cord—processes and coordinates information. The peripheral nervous system (PNS) carries messages between the CNS and the rest of the body. The somatic and autonomic systems are branches inside the PNS, not separate systems alongside it.

System Contains or controls Main distinction
Central nervous system (CNS) Brain and spinal cord Central processing and coordination
Peripheral nervous system (PNS) Neural pathways outside the CNS Relays messages between the CNS and the body
Somatic nervous system A branch of the PNS Governs voluntary processes
Autonomic nervous system A branch of the PNS; includes sympathetic and parasympathetic divisions Governs involuntary processes

Reaching for a cup is voluntary, so the outgoing control is classified as somatic PNS activity. Regulation of an involuntary process such as heart activity is classified as autonomic PNS activity. In both cases, peripheral pathways communicate with the CNS; ‘peripheral’ describes the connection network, not unimportant processing.

Common error: placing the sympathetic and parasympathetic systems directly under the whole nervous system. Both are subdivisions of the autonomic nervous system, which is itself part of the PNS.