4
The Peripheral Nervous System Communi-
cates with the Outside World 214
• The peripheral nervous system relays information to the
central nervous system through cranial and spinal nerves.
Cranial and spinal nerves can contain only sensory neurons,
only motor neurons, or both.
• Cranial nerves consist of 12 pairs of nerves that govern
sensory and motor information in the head, transmit infor-
mation to and from special sensory organs (eyes, nose, ears,
mouth, and so on), and provide output of some parasympa-
thetic functions. Spinal nerves like the one shown contain
sensory and motor neurons that transmit information from
specific spinal cord segments to different areas of the body.
• Reflexes produce involuntary responses to various stimuli.
The response is the result of passing impulses through
reflex arcs, which consist of sensory receptors, sensory
neurons, integrating centers, motor neurons, and effectors.
Key Terms
acetylcholine (ACh) 198
• cerebellum 203
action potential 197
• cerebrum 202
afferent neuron 195
• corpus callosum 202
afferent (sensory) nervous
• cranial nerves 192
system 193
• dendrite 195
Alzheimer disease (AD) 204
• dermatome 217
arachnoid villus 200
• diencephalon 202
astrocyte 196
• efferent (motor) nervous
autonomic nervous system
system 193
(ANS) 208
• efferent neuron 195
axon collateral 194
• enteric nervous system
axon hillock 194
(ENS) 193
axon 195
• enteric plexuses 192
axon terminal 198
• ependymal cell 196
basal ganglia 203
• frontal lobe 202
bipolar neuron 195
• ganglion 195
blood-brain barrier 196
• graded potential 197
brain 192
• gray matter 207
brainstem 202
• gyrus 203
cell body 195
• homunculus 204
central nervous system
• intercostal nerve 217
(CNS) 192
• interneuron 195
cerebellar peduncles 202
• lobe 203
Parts of a nerve • Figure 7.17
medulla oblongata 206
• reflex 218
meninges 200
• reflex arc 219
microglia 196
• resting membrane poten-
midbrain 202
tial 197
motor neuron 195
• satellite cell 196
multipolar neuron 195
• Schwann cell 196
myelin 195
• sensory neuron 195
nerve 193
• sensory receptor 195
nerve fiber 195
• somatic nervous system
neuroglia 192
(SNS) 193
neuron 192
• spinal cord 206
neurotransmitter 198
• spinal nerve 216
node of Ranvier 194
• stimulus 197
nucleus 195
• sulcus 203
occipital lobe 202
• sympathetic division 210
oligodendrocyte 196
• synapse 198
parasympathetic division 213
• temporal lobe 202
parietal lobe 202
• terminal ganglion 213
peripheral nervous system
• thalamus 202
(PNS) 192
• threshold 197
pineal gland 202
• unipolar neuron 195
plexus 216
• ventricle 200
pons 202
• white matter 207
222 CHAPTER 7
The Nervous System
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