HUMAN BIOLOGY

the nerVOus system 249

What are the major parts of the nervous

system?

• The two divisions of the nervous system are the central nervous
  system (CNS) and the peripheral nervous system (PNS).


• The central nervous system consists of the brain and
  spinal cord.


• The peripheral nervous system consists of branching spinal
  and cranial nerves that carry signals to and from the CNS.

taKe-hoMe Message

An effort called the Human Connectome Project

aims to map the brain’s internal communication

networks. This will be a huge task, given that

each of the brain’s 100 billion neurons makes an

estimated 10,000 connections with other neurons.

Researchers hope the project will provide better

understanding of the causes of disorders including

autism, schizophrenia, and other conditions

involving skewed neural “wiring.” On your own

or with a classmate, use the Web to learn more

about this project. A good starting point is www

.humanconnectomeproject.org.

ThiNk OuTSiDE ThE BOOk

cranial

nerves

ulnar

nerve

lumbar

nerves

(five pairs)

sacral nerves

(five pairs)

sciatic

nerve

(one in

each leg)

thoracic nerves

(twelve pairs)

cervical nerves

(eight pairs)

coccygeal nerves

(one pair)

brain

spinal

cord

Figure 13.12 Twelve pairs of cranial

nerves extend from different regions

of the brain stem. Roman numerals

are used to designate cranial nerves.

(© Cengage Learning)

F i g u r e 13.11 The brain, spinal cord, and nerves are the major components of the nervous system. (© Cengage Learning)

I Olfactory nerve

V To jaw

muscles;

from mouth

XII To neck and back muscles

II Optic nerve (from

the retina)

IV To eye muscles

III To eye muscles

VI To eye muscles

VII To facial

muscles, glands;

from taste buds

VIII From inner ear

IX To/from pharynx

X To tongue muscles

XI To/from internal organs

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