CNS: The brain and the spinal chord.

Peripheral Nervous System: All other nerves, consisting of the Autonomic Nervous System (ANS) and Somatic Nervous System (SNS).

Autonomic Nervous System: Involuntary innervation of visceral structures.

Innervates smooth (involuntary) muscle, cardiac muscle, and glands.

GVE: General Visceral Efferent -- Responsible for motor function to visceral tissues.

"Efferent" refers to flow from CNS to tissues, so that they will stimulate or effect a response.

GVA: General Visceral Afferent -- responsible for sensory function from visceral tissues.

"Afferent" refers to flow from the tissues back to the CNS, so they carry the impulse away from the stimulus.

These are made up primarily of stretch receptors, so that inflammation or distension of organs can be sensed.

Somatic Nervous System: Voluntary innervation of somatic structures (skeletal muscles and skin).

GSE: General Somatic Efferent -- responsible for motor function to somatic tissues.

GSA: General Somatic Afferent -- responsible for sensory function from somatic tissues.

Types of Nerves fibers: There are many types of nerve fibers in a single nerve bundle.

Motor Fibers

Sensory Fibers

Pain receptors -- originating from somatic structures.

Temperature -- originate from somatic structures.

Stretch receptors -- originating from visceral structures. These are important to visceral structures, as they constitute the main sensory input from the

organs.

MIXED NERVE: Nerves such as vagus and phrenic carry both afferent and efferent fib3ers, and both somatic and autonomic. Therefore they are mixed nerves.

REFERRED PAIN: The interpretation of dermatomal layers in the brain is responsible for the concept of referred pain.

Sensory input from the visceral organs is interpreted by the brain as originating from one of the dermatomal segments. The brain oversimplifies the stimulus as

coming from a cutaneous layer.

Take Appendicitis as an example:

Inflamed appendix sends an impulse to T10, which is then sent to brain to be processed.

Umbilical cutaneous dermatomal region also goes to T10, and in the past the brain has received more info from this region, so it "assumes" that the

appendix signal is coming from such a region.

So, there is an initial referred dull (visceral) pain in the umbilical region.

Then if the appendix inflames enough to pierce or press against the anterior wall, it will stimulate pain-afferent nerves in the lower right quadrant, so that

will create a sharp (somatic) pain in the region of the appendix.

These two signs together could be taken as signs of appendicitis.

STRUCTURE OF PARAVERTEBRAL GANGLIA:

Dorsal Root Ganglion: They have afferent (incoming sensory) nerves.

Two afferent nerves come in -- one from the peripheral tissues and one from the central canal.

Ventral Root Ganglion: Carries efferent fibers out to the periphery.

Spinal Nerves form where these two roots come together, to form both sensory and motor fibers in the same nerve.

All spinal nerves are mixed nerves!

Soon after forming, the spinal nerve divides into two nerves -- the pre-ganglionic nerves.

dorsal primary ramus -- innervates muscles and skin of back.

ventral primary ramus -- innervates lateral and anterior.

Ventral Primary Ramus goes to the White Rami Communicans on the sympathetic chain.

So the White Rami carries the efferent pre-ganglionic nerves.

Once the nerve-fiber reaches the sympathetic trunk, it has several options:

It can synapse with a Grey Rami Communicans and continue as a sympathetic spinal nerve going out to target viscera.

It can ascend to a higher level in the sympathetic chain.

It can descend to a lower level in the sympathetic chain.

It can pass through and out of the paravertebral ganglion without synapsing, and then continue onto a target organ as a splanchnic nerve -- to go to

visceral target organ and form a visceral plexus -- or branch somewhere nearby, like celiac or superior mesenteric arteries.

SYMPATHETIC

PARASYMPATHETIC

Spinal Chord Origin

Thoracolumbar: T5-T12, L1-L2

Craniosacral: C10 (Vagus Nerve), S2-S4.

Effects

Widespread, low precision

Specific, discrete, local, acute.

Location of cell bodies

Along the spinal chord, at the sympathetic chain ganglia.

Plexuses are found along the midline of the body -- pre-aortic

ganglia, mesenteric plexuses.

Adjacent to or in the target organ.

Pre-Ganglionic Fiber

Short

Long

Post-Ganglionic Fiber

Long

Short

Pre-Ganglion : Post-Ganglion fiber

ratio

Low ratio -- one pre-ganglion spreads to lots of post-ganglion,

hence the effect is widespread and imprecise

High Ratio -- 1:1 or near 1:1, hence the effect is more

localized.

Neurotransmitter

Acetylcholine at pre-synapse terminals

Norepinephrine at post-synapse terminals

Acetylcholine

General energy use and metabolism

Fight or flight -- expenditure of energy.

Intake and conservation of energy

The Vagus Nerve: Foregut and Midgut innervation

In the thorax, the right vagus runs posterior to the esophagus, and the left vagus runs anterior to it.

Around the esophageal hiatus (T10), the two vagus nerves mix, and then they separate again, to form the right and left vagal trunks.

Left (Anterior) Vagal Trunk: Gives off Hepatic Branch and Principle Anterior Gastric Branch.

Right (Posterior) Trunk: Forms the Celiac Plexus ------> Superior Mesenteric Plexus.

These nerves are perivascular -- they follow the course of the arteries.

Pelvic Splanchnic Nerves: Hindgut innervation

The Pelvic Splanchnic Nerves are parasympathetic Sacral spinal nerves S2-S4.

They form Pelvic Plexuses ------> Inferior Hypogastric Plexus ------> Pelvic viscera, and separately, the hindgut.

These nerves are Non-Perivascular. They do not follow the arteries, but instead crisscross the arteries. The nerves are still located in mesentery.

The lower anus (below pectinate line) is innervated by somatic nerves -- the pudendal nerve -- not parasympathetic pelvic splanchnic.

Greater Thoracic Splanchnics: T6-T9. Sympathetic spinal nerves supplying the foregut and midgut.

Lesser Thoracic Splanchnic: T10-T11. Sympathetic spinal nerves supplying the hindgut, generally.

Least Thoracic Splanchnic: T12. It supplies the Renal Plexus.