FoundationalConceptsNeuroscience

one of the principal divisions of the body’s neural network.
What are these divisions? There is the central nervous system
(CNS), consisting of the brain and spinal cord. And there is the pe-
ripheral nervous system (PNS), which encompasses all other parts
of the body’s neural networks. The PNS includes the various sensory
systems of the head (eyes, ears, nose, tongue) and their connections
to the brain; the several types of sensory input from the body’s skin
—systems responding to touch, temperature, and pain; and all the
receptors located within the muscles, tendons, and joints that provide
information about muscle tension and body position. Also part of the
PNS are the connections from the brain and spinal cord to the muscles
throughout the body, allowing for the control of body movements
(neuromuscular system).
Another component of the PNS is the autonomic nervous system.
This system regulates various body organs and internal functions,
such as heart rate, blood pressure, respiration, and digestion. Much
of this is normally outside our awareness—things that are largely
automatic. The autonomic nervous system is divisible into two com-
plementary components—the sympathetic nervous system and the
parasympathetic nervous system. Most of the organs (for example,
eyes, heart, lungs, stomach, intestines, bladder, genitals) innervated
by the autonomic system receive both sympathetic and parasympa-
thetic input. The regulation of the autonomic nervous system ulti-
mately comes in large part from the brain.
A last component of the PNS is called the enteric nervous system.
This is an elaborate network of neurons and connections within the
gastrointestinal system. It is involved in regulating digestion, moving
food through the system, absorbing fluid, secreting hormones, and
presumably other things yet unknown. It is sometimes referred to as
part of the autonomic nervous system. Although the enteric system