Subsystems of the Nervous System

ØD. Subsystems of the Nervous System: The nervous system is divisible into 2 overlapping pairs of subsystems:

Ø1. The central and peripheral nervous systems are defined mainly by location. The central nervous system (CNS) includes the brain and spinal cord. The peripheral nervous system (PNS) includes all other nerve tissue. 2. The autonomic and somatic nervous systems are defined according to function, but have distinctive anatomic features as well.

Each has CNS and PNS components. The autonomic nervous system controls involuntary visceral functions leg, glandular secretions, smooth muscle contraction) and has both motor and sensory pathways, although some authors exclude visceral sensory pathways from the ANS. Each motor pathway consists of 2 neurons that synapse in a peripheral autonomic ganglion. The cell body of the first (preganglionic) neuron is in the CNS; the cell body of the second (postganglionic) neuron is in the autonomic ganglion. The cell bodies of the sensory neurons are located in craniospinal ganglia and have processes that extend peripherally.

The ANS is subdivided into the sympathetic and parasympathetic nervous systems. When they innervate the same end organ, sympathetic and parasympathetic nerves usually have opposing effects. The somatic nervous system includes all nerve tissue except the ANS. It controls somatosensory perception leg, touch, heat, cold) and somatomotor (voluntary) functions (eg, skeletal muscle contraction). Acetylcholine is the most common somatic neurotransmitter.