Nervous System I
GENERAL FUNCTIONS OF
THE NERVOUS SYSTEM
The three general functions of the nervous system—receiv-
ing, deciding, and reacting to stimuli—are termed sensory,
integrative, and motor. Structures called
at the ends of peripheral neurons provide the sensory func-
tion of the nervous system (see chapter 11, p. 389). These
receptors gather information by detecting changes inside and
outside the body. They monitor external environmental fac-
tors such as light and sound intensities as well as the tem-
perature, oxygen concentration, and other conditions of the
body’s internal environment.
Sensory receptors convert (or transduce) their infor-
mation into nerve impulses, which are then transmitted
over peripheral nerves to the CNS. There the signals are
integrated—that is, they are brought together, creating sen-
sations, adding to memory, or helping produce thoughts.
Following integration, conscious or subconscious decisions
are made and then acted upon by means of motor functions.
The motor functions of the nervous system are car-
ried out by neurons that carry impulses from the CNS to
responsive structures called
These effectors are
outside the nervous system and include muscles that con-
tract in response to nerve impulse stimulation and glands
that secrete when stimulated. The motor portion of the PNS
Central Nervous System
(brain and spinal cord)
Peripheral Nervous System
(cranial and spinal nerves)
A diagrammatic representation of the nervous system. (
) The nervous system includes the central nervous system (brain and spinal
cord) and the peripheral nervous system (cranial nerves and spinal nerves). (
) The nervous system receives information from sensory receptors and
initiates responses through eF
ector organs (muscles and glands).
Neurons are the structural and functional units of the
nervous system (600×). Neuroglia are cells that surround and support
a neuron, appearing as dark dots. Note the locations of the neuron
processes (dendrites and a single axon).