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Home , Autonomic ganglion, Autonomic nervous system, Ramus communicans, White ramus communicans

Autonomic

Autonomic = self governing

Responsible for visceral motor funcon

Two parts: • sympathec and parasympathec • antagonists • one smulates/one inhibits CNS

PNS

Afferent Efferent Sensory division Motor division Afferent • carry nerve impulses from receptors or sense organs towards the CNS

visceral efferent

c efferent Efferent •carry nerve impulses away from the CNS to effectors such as muscles or glands CNS

PNS

Afferent Efferent Sensory division Motor division

Visceral= Somac Autonomic voluntary involuntary Somac skeletal 1 muscle voluntary Autonomic peripheral smooth 1 2 muscle, , PREganglionic POSTganglionic glands CNS outside CNS INvoluntary Structure Funcon

Somac 1 cell in pathway voluntary 1. (ventral horn) or

Visceral/ 2 cells in pathway involuntary Autonomic 1. spinal cord or brain 2. peripheral ganglion* cardiac muscle glands

*The autonomic system is a two system vs. the one neuron used in connecng the PNS to the CNS (motor and sensory) . ANS divisions must then use a "ganglion" where the preganglionic fiber with the postganglionic cell body. There are various types of ganglia (accumulaons of nerve cell bodies outside the CNS) associated with these sites: paravertebral ganglia (sympathec trunk ganglion), that lie on either side of the . They are used only for synapses of the sympathec division of the ANS prevertebral ganglia (“collateral ganglia”) that lie anterior to the vertebral column, close to major abdominal arteries from which they get their name (i.e. celiac, superior mesenteric, inferior mesenteric ganglion). For the synapse of fibers from the sympathec division intramural ganglia (terminal ganglia) located at the end ohe visceral efferent pathway, close to, or within the effector . These are sites of parasympathec synapse. CNS

PNS

Afferent Efferent Sensory division Motor division

Visceral= Somac Autonomic voluntary involuntary

Sympathec Parasympathec “fight or flight” “rest and digest” Sympathec “Fight or Flight” • rate speeds up • breathes faster • dilate • digeson slows • cold, sweaty • releases sugars into the blood

Parasympathec “Rest and Digest”

• slows • breathing slows • blood flow to digesve system increases • pupils constricted Sympathec sympathec chain ganglia near spinal cord

short preganglionic long postganglionic

Parasympathec ganglia near target

long preganglionic short postganglionic Sympathec

Parasympathec Sympathec Parasympathec thoracolumbar craniosacral Parasympathetic Division

Cell bodies for the parasympathetic division of the ANS are localized in the nuclei of the brain stem (cranial nn.) and in spinal cord segments S2-4 (i.e. craniosacral distribution)

The preganglionic parasympathetic fiber travels out via cranial (from the brain stem nuclei), and by pelvic splanchnic nn. from the sacral cord levels. may then contain motor, sensory and parasympathetic fibers, or any combination of these - but never contain sympathetic fibers.

4 cranial nerves with parasympathetic fibers: CN III (oculomotor n.) CN VII (facial n.) CN IX (glossopharyngeal n.) CN X (vagus n.)

There are 4 in the head (COPS) associated with the cranial nerves but only 3 of the parasympathetic nn. are associated (synapse) in them: ciliary (CN III) submandibular (CN VII) otic (CN IX) pterygopalatine (CN VII)

The parasympathetic fibers in the vagus n. (CN X) are not confined to the head but spread parasympathetic innervation to 2/3 of the body ( and ). The vagus uses intramural ganglia exclusively.

Sympathec chain ganglia – 22 – 24 cervical – 3 thoracic – 11 lumbar – 4 sacral – 4 coccygeal - 1

The sympathetic chain extends from the base of the skull to the base of the coccyx. Its function is to distribute sympathetic innervation throughout the body since it is only found in the spinal cord segments Tl-L2. An example of this is the sympathec innervaon for the head and . It arises from the spinal cord segments T1-T4. The preganglionic fibers enter the sympathec trunk via the white rami communicans at these levels and ascends to synapse in the superior cervical ganglion at the base of the skull before extending onto the face as a postganglionic sympathec fiber.

Gray rami are found at every vertebral level that exhibits a sympathetic ganglion. This extends from the base of the skull through to the tip of the coccyx. Gray rami communicans are output fibers for the sympathetic division of the ANS. There are more gray rami than white as white rami input sympathetic innervation and are restricted to TI-L2 where the sympathetic cell bodies are located. Sympathetic Division

Cell bodies for the sympathetic division of the ANS are localized in the intermediolateral grey horn of the spinal cord from segments TI-L2 only. It is referred to as being thoracolumbar in distribution.

The preganglionic sympathetic fiber travels out into the along the ventral root in company with the motor fiber. Once in the ventral ramus the preganglionic fiber enters a sympathetic ganglion (paravertebral ) via the white . In the thorax and abdomen there is one sympathetic ganglion per vertebral level (i.e. 12 thoracic and 5 lumbar ). The ramus is termed "white" because the preganglionic fiber that traverses it is myelinated having arrived there from the spinal cord. White rami input sympathetic impulse into the sympathetic chain from T1-L2.

Once in the , one of three things can happen…

1. The preganglionic fiber synapses in the sympathetic (paravertebral autonomic) ganglion and the postganglionic fiber re- enters the ventral (and dorsal) ramus via the grey (non-myelinated) ramus communicans to supply sympathetic innervation to the body wall.

2. The preganglionic fiber ascends or descends within the sympathetic trunk to synapse in a sympathetic (paravertebral autonomic) ganglion at a level other than that at which it entered the trunk. The post- ganglionic fiber re-enters the ventral (and dorsal) ramus via the grey (nomnyelinated) ramus communicans. These fibers may be directed to viscera or the body wall.

Once in the sympathetic trunk, one of three things can happen…

3. The preganglionic fiber passes through the sympathetic (paravertebral autonomic) ganglion via a splanchnic nerve to a prevertebral autonomic ganglion where it synapses. The postganglionic fiber then passes out along to the target organ - usually a visceral organ in this instance. Structure Funcon

• short preganglionic, long “fight or flight:” postganglionic increase heart rate Sympathec • 2nd cell body in increase respiraon sympathec chain dilate pupils

• thoracolumbar inhibit blood to gut • branch profusely

• long preganglionic, short “rest and digest:” postganglionic decrease heart rate Para- • 2nd cell body in ganglia slow respiraon sympathec near target increase blood flow to • craniosacral digesve tract • do not branch much ANA 611/811 Autonomic Nervous System 20

Schematic for Sympathetic Autonomic Distribution

Somatomotor

Visceromotor

Somatosensory

Visceral sensory ??? CNS

PNS

Afferent Efferent Sensory division Motor division

Visceral= Somac Autonomic voluntary involuntary

Sympathec Parasympathec “fight or flight” “rest and digest” Functional Aspects of the Afferent/Efferent Divisions

Each spinal nerve contains two types of afferent (sensory) and efferent (motor) fibers: i) somatic afferent/efferent fibers that relay information to and from the body wall • somatic efferents: motor to skeletal muscle • somatic afferents: peripheral sensory receptors feeding the CNS

Functional Aspects of the Afferent/Efferent Divisions

Each spinal nerve contains two types of afferent (sensory) and efferent (motor) fibers: ii) visceral afferent/efferent fibers that relay information to and from the viscera of the body

• visceral efferents (MOTOR): preganglionic visceral (sympathetic) fibers (TI-L2) that enter the sympathetic trunk via the white rami communicans. These fibers synapse in prevertebral ganglia and the postganglionic fibers go to the target organ. Parasympathetic viscerals (S2-4) leave the ventral rami and synapse in the target organ

• visceral afferents (SENSORY): come back from the viscera via the white rami communicans and can travel up or down the sympathetic trunk prior to synapsing in the spinal cord Splanchnic (visceral) nerves

Splanchnic nerves extend from the paravertebral (sympathetic) ganglia out to the prevertebral ganglia (celiac, superior and inferior mesenteric).

They carry sympathetic pre- and postganglionic fibers to this ganglion as well as visceral afferent (sensory) fibers back from the visceral to the CNS. The preganglionic sympathetic fibers synapse in the prevertebral ganglion, the postganglionic sympathetic fibers simply pass through. In addition, preganglionic parasympathetic fibers access the prevertebral ganglion and also pass through. Referred : A term used to describe the phenomenon of pain perceived at a site adjacent to or at a distance from the site of an injury's origin Concepts Involved in

1. Proximal - Distal

Where the injury is proximal and pain is felt distally.

One example is a herniated disc. Herniation of the intervertebral disc between L4 and L5 involves the protrusion of the nucleus pulposus (center of disc) posteriorly into the vertebral foramen. Lumbar spinal nerves pass down the vertebral foramen in the cauda equina to exit at lower levels of the vertebral column than the termination of the spinal cord at L2. Posterior protrusion of the disc between L4 and L5 will cause compression of the dorsal and ventral roots of L5. Pain is felt along the supplied by L5. Concepts Involved in Referred Pain

1. Somatic (embryological)

The diaphragm forms embryologically from the fusion of three different structures in the cervical (neck) region from the myotomes of C3, 4, and 5.

The heart forms above it in the neck region and descends into the thorax pushing the diaphragm down ahead of it. This effectively stretches its innervation to accompany it.

The (C3,4,5) supplies total motor innervation to the diaphragm and supplies sensory innervation to the pleural membrane covering its central region.

Inflammation/irritation of the central diaphragmatic (parietal) pleura, in diseases like pleurisy, may have the pain referred to the neck region due to the origin of the roots of the phrenic nerve.

Concepts Involved in Referred Pain

1. Visceral/Somatic (sensory afferents)

A good example of this type of referred pain is the pain felt from accidental impact of the testis.

Although the testis are injured the pain is first felt in the abdominal region. Later the pain is localized in the bruised/injured testis. Other examples are:

• pain from appendicitis is first referred to the umbilical region • pain from cardiac infarction occurs down the medial side of the left arm pain from cardiac infarction

Cardiac nerves Cell bodies for fibers pass to take visceral these nerves are pain in adventitia superficial and afferents to the in T1 – 4/5. Pain and myocardium deep cardiac upper gangila of is referred of Heart plexuses the sympathetic Through derma- trunk tomes T1 – 4/5. Sympathetic innervation of major viscera

A diagrammatic representation of the spinal cord levels responsible for supplying sympathetic fibers to the major viscera.

Sympathetic Chain • PARAvertebral ganglia

Unpaired ganglia • PREvertebral ganglia Parasympathetic • Vagus n. (CN X)

• S2,3,4 Sympathetic (T1-L2) • Thoracolumbar outflow

Sympathetic Chain • PARAvertebral ganglia

Unpaired ganglia • PREvertebral ganglia Parasympathetic • Vagus n. (CN X)

• S2,3,4 Peripheral nerves • Postganglionic/synaptic sympathetic • Somatic motor (efferent) • Somatic sensory (afferent)

TO: “Boring” regular stuff that is everywhere…muscles, blood vessles, glands, body wall...and (one exception) the head

Sympathetic Chain • PARAvertebral ganglia

Unpaired ganglia • PREvertebral ganglia Parasympathetic • Vagus n. (CN X)

• S2,3,4 • Preganglionic/synaptic sympathetic • visceral afferents (sensory)

TO: “Cool” unique stuff that live in body cavities (visceral organs) POSTganglionic/synapitc sympathetic PREganglionic/synapitc parasympathetic Visceral afferents (sensory)