Essentials of Anatomy and Physiology

188 The Nervous System

Optic

chiasma

Figure 8–11. Cranial

nerves and their distributions.

The brain is shown in an infe-

rior view. See Table 8–4 for

descriptions.

QUESTION: Which cranial

nerves bring about secretion

of saliva? Which nerve brings

about gastric and intestinal

secretion?

bodies are in the thoracic segments and some of the
lumbar segments of the spinal cord. Their axons
extend to the sympathetic ganglia, most of which are
located in two chains just outside the spinal column
(see Fig. 8–12). Within the ganglia are the synapses
between preganglionic and postganglionic neurons;
the postganglionic axons then go to the visceral effec-
tors. One preganglionic neuron often synapses with
many postganglionic neurons to many effectors. This
anatomic arrangement has physiological importance:
The sympathetic division brings about widespread
responses in many organs.

The sympathetic division is dominant in stressful

situations, which include anger, fear, or anxiety, as

well as exercise. For our prehistoric ancestors, stress-

ful situations often involved the need for intense phys-

ical activity—the “fight or flight response.” Our

nervous systems haven’t changed very much in 50,000

years, and if you look at Table 8–5, you will see the

kinds of responses the sympathetic division stimulates.

The heart rate increases, vasodilation in skeletal mus-

cles supplies them with more oxygen, the bronchioles

dilate to take in more air, and the liver changes glyco-

gen to glucose to supply energy. At the same time,