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Would autonomic postganglionic fibers have faster or slower conduction speeds than somatic motor fibers?

Why? (See hints in chapter 12.)

3 para = next to + vertebr = vertebral column

4 ramus = branch

Thoracic Cavity Lateral View Anatomy
Figure 15.3 The Sympathetic Chain Ganglia. Right lateral view of the thoracic cavity. (a. = artery; n. = nerve; v. = vein.)

Saladin: Anatomy & I 15. The Autonomic Nervous I Text

Physiology: The Unity of and Visceral Reflexes Form and Function, Third Edition

Regions of spinal cord

Cervical I Thoracic Lumbar ]] Sacral

Regions of spinal cord

Postganglionic fibers to skin, blood vessels, adipose tissue

Sympathetic Preganglionic Neurons

Salivary glands

Heart

Spinal cord

Sympathetic chain ganglia

Preganglionic neurons = red Postganglionic neurons = black

Figure 15.4 Sympathetic Pathways.

Does the sympathetic innervation of the lung cause inhaling and exhaling?

Salivary glands

Heart

Postganglionic fibers to skin, blood vessels, adipose tissue

Spinal cord

Sympathetic chain ganglia

Collateral ganglia: (T) Celiac ganglion @ Superior mesenteric ganglion (3l Inferior mesenteric ganglion

Preganglionic neurons = red Postganglionic neurons = black

Lung

Liver and gallbladder

Stomach Spleen

Pancreas

Small intestine Large intestine Rectum

Adrenal medulla Kidney

Figure 15.4 Sympathetic Pathways.

Does the sympathetic innervation of the lung cause inhaling and exhaling?

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Physiology: The Unity of and Visceral Reflexes Companies, 2003 Form and Function, Third Edition

Chapter 15 The Autonomic Nervous System and Visceral Reflexes 569

Somatic — motor fiber

To somatic effector (skeletal muscle)

I Preganglionic neuron Postganglionic neuron Somatic neuron

Somatic — motor fiber

To somatic effector (skeletal muscle)

Paravertebral Ganglion

Soma of-1 somatic motor neuron

Splanchnic nerve

Collateral ganglion

Postganglionic-

sympathetic fibers

Soma of preganglionic j

Soma of-1 somatic motor neuron

Splanchnic nerve

Collateral ganglion

Postganglionic-

sympathetic fibers

To visceral effectors (smooth muscle, cardiac muscle, glands)

Soma of preganglionic j

Communicating Rami

Preganglionic sympathetic fiber

Postganglionic sympathetic fiber

White ramus Gray ramus

Soma of postganglionic neuron

Sympathetic trunk

Preganglionic sympathetic fiber

Postganglionic sympathetic fiber

White ramus Gray ramus

Communicating rami

Soma of postganglionic neuron

Sympathetic trunk

Sympathetic ganglion

Figure 15.5 Sympathetic Pathways (right) Compared to Somatic Efferent Pathways (left). Sympathetic fibers can follow any of the three numbered routes: (1) the spinal nerve route, (2) the sympathetic nerve route, or (3) the splanchnic nerve route. Name the parts of the spinal cord where the somas of the sympathetic and somatic efferent neurons are located.

After entering the sympathetic chain, preganglionic fibers may follow any of three courses:

• Some end in the ganglion that they enter and synapse immediately with a postganglionic neuron.

• Some travel up or down the chain and synapse in ganglia at other levels. It is these fibers that link the paravertebral ganglia into a chain. They are the only route by which ganglia at the cervical, sacral, and coccygeal levels receive input.

• Some pass through the chain without synapsing and continue as splanchnic (SPLANK-nic) nerves, to be considered shortly.

There is no simple one-to-one relationship between preganglionic and postganglionic neurons in the sympathetic division. For one thing, each postganglionic cell may receive synapses from multiple preganglionic cells, thus exhibiting the principle of neuronal convergence discussed in chapter 12. Furthermore, each preganglionic fiber branches and synapses with multiple postganglionic fibers, thus showing neuronal divergence. There are about

17 postganglionic neurons for every preganglionic neuron in the sympathetic division. This means that when one preganglionic neuron fires, it can excite multiple postgan-glionic fibers leading to different target organs. The sympathetic division thus tends to have relatively widespread effects—as suggested by the name sympathetic.5

Nerve fibers leave the paravertebral ganglia by three routes: spinal, sympathetic, and splanchnic nerves. These are numbered in figure 15.5 to correspond to the following descriptions:

1. The spinal nerve route. Some postganglionic fibers exit by way of the gray ramus, return to the spinal nerve or its subdivisions, and travel the rest of the way to the target organ. This is the route to most sweat glands, piloerector muscles, and blood vessels of the skin and skeletal muscles.

2. The sympathetic nerve route. Other postganglionic fibers leave by way of sympathetic nerves that

5sym = together + path = feeling

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

570 Part Three Integration and Control extend to the heart, lungs, esophagus, and thoracic blood vessels. These nerves form a plexus around each carotid artery and issue fibers from there to effectors in the head—including sweat, salivary, and nasal glands; piloerector muscles; blood vessels; and dilators of the iris. Some fibers from the superior cervical ganglion form the cardiac nerves to the heart.

The splanchnic6 nerve route. This route is formed by fibers that originate predominantly from spinal nerves T5 to T12 and pass through the ganglia without synapsing. Beyond the ganglia, they form greater, lesser, and lumbar splanchnic nerves. These splanchn = viscera lead to the collateral (prevertebral) ganglia, which contribute to a network called the abdominal aortic plexus wrapped around the aorta (fig. 15.6). There are three major collateral ganglia in this plexus—the celiac (SEE-lee-ac) ganglion, superior mesenteric ganglion, and inferior mesenteric ganglion— located at points where arteries of the same names branch off the aorta. The postganglionic fibers accompany these arteries and their branches to the target organs. (The term solar plexus is regarded by some authorities as a collective designation for the celiac and superior mesenteric ganglia, and by others as a synonym for the celiac ganglion only. The term comes from the nerves radiating from the ganglion like rays of the sun.) Innervation to and from the three major collateral ganglia is summarized in table 15.2.

Celiac Ganglion
Figure 15.6 Sympathetic Collateral Ganglia and the Abdominal Aortic Plexus.

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Physiology: The Unity of and Visceral Reflexes Companies, 2003 Form and Function, Third Edition

Chapter 15 The Autonomic Nervous System and Visceral Reflexes 571

Table 15.2 Innervation To and From the Collateral Ganglia

Sympathetic Ganglia and Splanchnic Nerve

^ Collateral Ganglion ^

Postganglionic Target Organs

From thoracic ganglia 5 to 9 or 10 via greater splanchnic nerve From thoracic ganglia 9 and 10 via lesser splanchnic nerve From lumbar ganglia via lumbar splanchnic nerve

Celiac ganglion

Celiac and superior mesenteric ganglia Celiac and inferior mesenteric ganglia

Stomach, spleen, liver, small intestine, and kidneys

Small intestine and colon

Distal colon, rectum, urinary bladder, and reproductive organs

In summary, effectors in the body wall are innervated mainly by sympathetic fibers in the spinal nerves; effectors in the head and thoracic cavity by sympathetic nerves; and effectors in the abdominal cavity by splanchnic nerves.

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Responses

  • Merry
    Is the sympathetic chain ganglia located in the thoracic cavity?
    8 years ago
  • fernando ricci
    Which of the following descriptions of a preganglionic neuron is NOT correct?
    6 years ago
  • iggi
    Is autonomic postganglionic fibers have faster or slower conduction speeds than somatic motor fibers?
    6 years ago
  • bisrat
    Where is the celiac ganglion and plexus located?
    5 years ago

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