Autonomic Nervous System

Postganglionic parasympathetic fibers

1. Cranial - Travel from the above ganglia in other nerves until they reach their target. 2. Other - Since the postganglionic ganglia elsewhere are embedded in the walls of their target organs, the postganglionic fibers also are in the walls, so you will not see them.

Preganglionic parasympathetic fibers

1. Exit in cranial nn. III, VII, IX, or X and may hop on other nerves to get to ganglion 2. Exit sacral spinal nerves (S2-S4) to supply pelvic viscera & colon distal to the splenic flexure

Sympathetic nervous system: Preganglionic sympathetic fibers pathway

1. Exit the spinal cord through the ventral root 2. Enters the sympathetic chain via white rami and goes into the sympathetic ganglion

Sympathetic nervous system: Location of preganglionic sympathetic cell bodies

1. Located in the intermediolateral cell column (IMLCC) (intermediate to dorsal and ventral horns) 2. Extends from T1 - L3

Sympathetic nervous system: Postganglionic sympathetic cell bodies located in two places

1. Paravertebral ganglia (sympathetic chain ganglia) 2. Prevertebral ganglia (via splanchnic nn)

Nervous System Divisions: Functionally

1. Sensory (afferent) a. General Sensory b. Special Sensory 2. Motor (efferent) a. voluntary b. involuntary (autonomic) i. sympathetic ii. parasympathetic

Sympathetic nervous system: General points

1. Thoracolumbar origination (T1 - L3 spinal cord) 2. Sympathetic fibers destined for the head & neck tend originate about T1 - T4 3. Distribution to entire body 4. "Fight or flight" - mobilizes body for sudden action

General Characteristics of both divisions

A. Involuntary system innervating smooth mm, cardiac mm, glands. B. Classically described as a motor system, although sensory fibers may also travel within it. C. A two neuron system 1. Cell bodies of the first neuron lie in the CNS (ALWAYS) 2. Cell bodies of the second neuron are collected together in a group called a ganglion D. We speak, therefore, of the first neuron having a preganglionic cell body and a preganglionic axon and the second neuron having a postganglionic cell body & axon. F. Both systems usually go to the same organ but have antagonistic functions; i.e. sympathetic impulses to the heart speed it up and parasympathetic impulses slow it down.

Nervous System Divisions: Anatomically

CNS - Brain and Spinal Cord PNS - Cranial nerves and Spinal Nerves

Origin of the parasympathetic division

Craniosacral origin (Brain S2,3,4)

Some differences between parasympathetic and sympathetic divisions: Functions

Parasympathetic: maintain homeostatic functions & response to stress, restore the reserves "feed or fornicate" Sympathetics: ready the body for fight or flight responses (sudden activity)

Some differences between parasympathetic and sympathetic divisions: Location

Sympathetic nerves are distributed throughout the entire body. Parasympathetic nerves stay somewhat internal and do not go into the extremities or body walls. Thus, sympathetics go to sweat glands, but parasympathetics do not—the sweat glands are either on or off

Some differences between parasympathetic and sympathetic divisions: Neurotransmitters

Sympathetic: Preganglionic synapse: Acetylcholine ACh Postganglionic synapse: Usually norepinephrine (NE) Parasympathetic Preganglionic synapse: Acetylcholine ACh Postganglionic synapse: Acetylcholine ACh

Some differences between parasympathetic and sympathetic divisions: Origin

The divisions begin in different places. Sympathetics arise from the thoracolumbar spinal cord, parasympathetics arise from the nuclei of the brainstem or the sacral spinal cord.

Origin of the sympathetic division

Thoracolumbar origin (T1 - L3)

Prevertebral ganglia (via splanchnic nn) Location

a. Celiac ganglion b. Superior mesenteric ganglion c. Aorticorenal ganglion d. Inferior mesenteric ganglion

Postganglionic sympathetic fibers: Fibers destined for everything besides the abdominal viscera

a. Exit sympathetic chain ganglia via gray rami b. Enter spinal nerves distributed over the entire body

Postganglionic sympathetic fibers: Fibers destined for the abdominal viscera

a. Exited sympathetic chain w/o synapsing as preganglionic fibers in splanchnic nn and synapsed in one of the prevertebral ganglia listed on previous notecard. b. Postganglionic fibers then exit those prevertebral ganglia and usually wrap themselves around an artery going to the desired organ.

Sympathetic nervous system: Within the ganglion the preganglionic sympathetic fiber may do one of the following

a. Synapse in the chain ganglion at the same spinal level b. Ascend in the chain and synapse in a ganglion at a higher level c. Descend in the chain and synapse in a ganglion at lower level d. Pass through the ganglion, NOT synapsing, and exit in one of the splanchnic nn. to synapse in a prevertebral ganglion to supply abdominal viscera

Paravertebral ganglia (sympathetic chain ganglia) characteristics

a. These ganglia are at all vertebral levels, cervical through coccyx b. Ganglion impar - the terminal ganglion where chains join (@ the coccyx) c. All paravertebral ganglia are associated with a spinal nerve

The primary mission in life of a preganglionic axon is to:

find a ganglion to synapse in (location of postganglionic cell bodies)

Autonomic fibers tend to run in...

nerves that already exist and are going the direction they need to go. For example, sympathetic fibers destined for the eye jump on and off various nerves that are heading toward the eye until they get there. In some cases, the fiber may jump on a blood vessel going to the the target organ and ride it to its final destination.