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neurons without relaying the information to the brain (see Figure 3.18 "The Reflex"). When you
touch a hot stove and immediately pull your hand back, or when you fumble your cell phone and
instinctively reach to catch it before it falls, reflexes in your spinal cord order the appropriate
responses before your brain even knows what is happening.
Figure 3.18 The Reflex
The central nervous system can interpret signals from sensory neurons and respond to them extremely quickly via
the motor neurons without any need for the brain to be involved. These quick responses, known as reflexes, can
reduce the damage that we might experience as a result of, for instance, touching a hot stove.
If the central nervous system is the command center of the body, theperipheral nervous system
(PNS) represents the front line. The PNS links the CNS to the body’s sense receptors, muscles,
and glands. As you can see inFigure 3.19 "The Autonomic Nervous System", the peripheral
nervous system is itself divided into two subsystems, one controlling internal responses and one
controlling external responses.