Porth's Essentials of Pathophysiology, 4e

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Organization and Control of Neural Function

C h a p t e r 3 4

TABLE 34-3 Characteristics of the Sympathetic and Parasympathetic Nervous Systems Characteristic Sympathetic Outflow Parasympathetic Outflow

Location of preganglionic cell bodies T1–T12, L1 and L2

Cranial nerves: III, VII, IX, X; S2 to S4 Long—to ganglion cells near or in the innervated organ Anabolic—concerned with conservation, renewal, and storage of resources

Relative length of preganglionic fibers Short—to paravertebral chain of ganglia or to aortic prevertebral of ganglia

General function

Catabolic—mobilizes resources in anticipation of challenge for survival (preparation for “fight-or-flight” response)

Nature of peripheral response Neurotransmitter at ganglion

Generalized

Localized

ACh

ACh

Receptor at ganglion Transmitter of postganglionic neuron

Nicotinic (N N ) NE (most synapses)* NE and Epi (secreted by adrenal gland) Alpha ( α ) and Beta ( β ) Smooth muscle, cardiac muscle, and secretory cells throughout body

Nicotinic (N N ) ACh

Type of transmitter receptors at target synapse Target effectors

Muscarinic (M)

Most viscera of the head and the thoracic, abdominal, and pelvic cavities

Ach, acetylcholine; NE, norepinephrine; Epi, epinephrine *Postganglionic sympathetic nerve fibers to sweat glands, piloerector muscles, and a few blood vessels are cholinergic.

sympathetic nervous system often is referred to as the thoracolumbar division of the ANS. These pregangli- onic neurons have axons that are largely myelinated and relatively short. The postganglionic neurons of the sym- pathetic nervous system are located in the paravertebral ganglia of the sympathetic chain that lie on either side of the vertebral column, or in prevertebral sympathetic

ganglia such as the celiac ganglia, the branches of which innervate the liver, stomach, and other visceral organs (Fig. 34-23). Besides postganglionic efferent neurons, the sympathetic ganglia contain interconnecting neurons similar to those associated with complex circuitry in the brain and spinal cord, many of which inhibit modulate preganglionic-to-postganglionic transmission.

To head (e.g., pupillary muscles) and carotid arteries with periarterial plexus

Above T1

Sympathetic trunk (chain) with paravertebral ganglia

Intermedio- lateral horn

Spinal nerve

Ventral horn

Spinal nerves to effector organs in body wall and limbs

Ventral and dorsal rami

Ventral root

Spinal cord

FIGURE 34-23. Sympathetic pathways. Sympathetic preganglionic fibers (blue) leave the spinal cord by way of the ventral root of the spinal nerves, enter the ventral primary rami, and pass through the white rami to the prevertebral or paravertebral ganglia of the sympathetic chain, where they synapse with postganglionic neurons (black). Other preganglionic neurons (red dotted lines) travel directly to their destination in the various effector organs.

Gray ramus communicans

Splanchnic nerves

White ramus communicans

Synapse

To stomach and other abdominal viscera

Prevertebral ganglion

Below L2

To lower limbs