Reflex arc • Figure 7.2 0
NNER
When you tap the patellar tendon with a rubber hammer, your knee jerks
involuntarily in a reflex arc called the patellar reflex.
(Stretching stimulates
SENSORY RECEPTOR
(muscle spindle)
To brain
Reflex arcs allow for fast, involuntary
processing and responses to stimuli.
• Spinal reflexes occur in the spinal
cord (patellar reflex shown here).
Cranial
reflexes occur in the brain
(such as pupil dilation and contraction
in response to changes in light intensity).
Suppose that the individual in this figure has suffered an
injury to the spinal cord segment that is shown, and the in-
tegrating center is damaged. Explain why the leg would not
move when the tendon is struck with the hammer.
neuronal circuits called reflex arcs (Figure 7.20). A re-
flex arc consists of a sensor receptor, a sensory neuron,
an integrating center (the brain or spinal cord), a mo-
tor neuron, and an effector. Some reflexes also involve
inhibitory interneurons. As the introductory examples
imply, some reflex arcs are important mechanisms that
protect us from harm. Others, such as the patellar re-
flex, help us maintain our balance when we stand up
(Figure 7.20).
CONCEPT CHECK
1.
What
is a bundle of axons in the peripheral ner-
vous system called?
2.
Which
cranial nerve is a sensory nerve for sight?
3.
Which
spinal nerves do not have plexuses?
4.
Where
is the integrating center for a cranial
nerve reflex?
The Peripheral Nervous System Communicates with the Outside World
219
PROCESS DIAGRAM
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