Chapter 15: The Autonomic Nervous System

**sympathetic division** and the **parasympathetic division**.

The two divisions of the autonomic nervous system

**fight-or-flight response**

 The sympathetic system is associated with the

**rest and digest**

parasympathetic activity is referred to by the epithet of

 **thoracolumbar system**

The sympathetic division of the autonomic nervous system influences the various organ systems of the body through connections emerging from the thoracic and upper lumbar spinal cord.

**central neuron**

in the lateral horn of any of these spinal regions projects to ganglia adjacent to the vertebral column through the ventral spinal roots.

**sympathetic chain ganglia**

 runs alongside the vertebral column.

**target effector**

The first type is most direct: the sympathetic nerve projects to the chain ganglion at the same level as the

**white rami communicantes**

 they are myelinated and therefore referred to as white.

**ganglionic neuron**

The axon from the central neuron (the preganglionic fiber shown as a solid line) synapses with the

 **gray rami communicantes**

unmyelinated axons

**superior cervical ganglion**

where it synapses with the postganglionic neuron

**paravertebral ganglia**

given their location adjacent to prevertebral ganglia in the sympathetic chain.

**greater splanchnic nerve** or **lesser splanchnic nerve**

Additional branches from the ventral nerve root continue through the chain and on to one of the collateral ganglia as the

**Collateral ganglia**

also called **prevertebral ganglia**, are situated anterior to the vertebral column and receive inputs from splanchnic nerves as well as central sympathetic neurons.

**celiac ganglion**, the **superior mesenteric ganglion,** and the **inferior mesenteric ganglion.**

The three collateral ganglia

**preganglionic fiber**

An axon from the central neuron that projects to a sympathetic ganglion

**postganglionic fiber**

—the axon from a ganglionic neuron that projects to the target effector—represents the output of a ganglion that directly influences the organ.

**chromaffin cells**

The cells in the adrenal medulla that are contacted by the preganglionic fibers

 **craniosacral system**

The parasympathetic system can also be referred to as the

**terminal ganglia**

 which are located near—or even within—the target effector.

**intramural ganglia**

when they are found within the walls of the target organ.

**Edinger–Westphal nucleus**

 is part of the oculomotor complex, and axons from those neurons travel with the fibers in the oculomotor nerve (cranial nerve III) that innervate the extraocular muscles.

**ciliary ganglion**

which is located in the posterior orbit.

 **dorsal nucleus of the vagus nerve** and the **nucleus ambiguus**

project through the vagus nerve (cranial nerve X) to the terminal ganglia of the thoracic and abdominal cavities.

 **mesenteric plexus**

The postganglionic fibers from the ganglia activated by the vagus nerve are often incorporated into the structure of the organ, such as the **__** of the digestive tract organs and the intramural ganglia.

the **nicotinic receptor** and the **muscarinic receptor**

The cholinergic system includes two classes of receptor

**ligand-gated cation channel**

The nicotinic receptor

 **G protein–coupled receptor**

muscarinic receptor is

**alpha (α)-adrenergic receptor** and **beta (β)-adrenergic receptor.**

The adrenergic system also has two types of receptors

**epinephrine**

An additional aspect of the adrenergic system is that there is a second signaling molecule

 **somatic reflex**

such as the withdrawal reflex

**visceral reflex**

which is an autonomic reflex, is in the **efferent branch.**

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**Afferent Branch**

of a reflex arc does differ between somatic and visceral reflexes in some instances.

**Efferent Branch**

 of the visceral reflex arc begins with the projection from the central neuron along the preganglionic fiber

 **long reflex**

has afferent branches that enter the spinal cord or brain and involve the efferent branches

**short reflex**

is completely peripheral and only involves the local integration of sensory input with motor output.

**Central Control**

 of autonomic reflexes is different than for somatic reflexes.

**Hypothalamus**

is the control center for many homeostatic mechanisms.

the **dorsal longitudinal fasciculus** and the **medial forebrain bundle**

Output from the hypothalamus follows two main tracts,

**Amygdala**

is a group of nuclei in the medial region of the temporal lobe that is part of the **limbic lobe.**

**Medulla**

contains nuclei referred to as the **cardiovascular center**, which controls the smooth and cardiac muscle of the cardiovascular system through autonomic connections.

 **cardiac accelerator nerves**

The preganglionic sympathetic fibers that are responsible for increasing heart rate

**vasomotor nerves**

whereas the preganglionic sympathetic fibers responsible for constricting blood vessels compose the

**endogenous chemical**

A chemical that the body produces to interact with those receptors

**exogenous chemical**

whereas a chemical introduced to the system from outside

 **sympathomimetic drug**

A drug that enhances adrenergic function

 **sympatholytic drug**

whereas a drug that interrupts adrenergic function

 **parasympathomimetic drugs**

Drugs that enhance cholinergic effects

**anticholinergic drugs**

whereas those that inhibit cholinergic effects