DENTAL & OPTOMETRYDENTAL & OPTOMETRYSTUDENTSSTUDENTS

INTRODUCTION TO INTRODUCTION TO AUTONOMIC NERVOUS SYSTEMAUTONOMIC NERVOUS SYSTEM

——

IE, SOMATIC NERVOUS SYSTEM IE, SOMATIC NERVOUS SYSTEM VERSUS AUTONOMIC NERVOUS VERSUS AUTONOMIC NERVOUS

SYSTEMSYSTEM

GEORGE SALTER, PH.DGEORGE SALTER, PH.D

DENTAL STUDENTSDENTAL STUDENTS

The Motor Aspect Of The The Motor Aspect Of The

Nervous System May BeNervous System May Be

Divided Into A Somatic Divided Into A Somatic PartPart

And An Autonomic PartAnd An Autonomic Part

SOMATIC NERVOUS SOMATIC NERVOUS SYSTEMSYSTEM

• TARGET ORGAN IS SKELETAL MUSCLETARGET ORGAN IS SKELETAL MUSCLE

• A SINGLE NEURON IS INVOLVEDA SINGLE NEURON IS INVOLVED

• THE ORIGIN OF THE SINGLE NEURON THE ORIGIN OF THE SINGLE NEURON IS THE CNS, SPECIFICALLY THE IS THE CNS, SPECIFICALLY THE ANTERIOR HORN CELLSANTERIOR HORN CELLS

PHLHAH

Anterior Horn Cell

Thoracic Cord

AUTONOMIC NERVOUS AUTONOMIC NERVOUS SYSTEMSYSTEM

FunctionallyFunctionally, , The Autonomic Nervous The Autonomic Nervous

SystemSystemMay Be Divided Into A May Be Divided Into A

SympatheticSympatheticPart And A Part And A ParasympatheticParasympathetic

Part.Part.

These Two “Divisions” Have These Two “Divisions” Have Opposite Effects—Eg. Opposite Effects—Eg.

SympatheticSympatheticFibers Increase The Heart Fibers Increase The Heart

Rate (Tachycardia) And The Rate (Tachycardia) And The Parasympathetic Fibers Parasympathetic Fibers

Decrease The Pulse Decrease The Pulse (Bradycardia).(Bradycardia).

ANS—Both Parasympathetic ANS—Both Parasympathetic &&

Sympathetic FibersSympathetic Fibers

• Target Organs Are Glands, Smooth Target Organs Are Glands, Smooth Muscle and Cardiac MuscleMuscle and Cardiac Muscle

Two Neurons, And Thus a Synapse, Are Two Neurons, And Thus a Synapse, Are

Involved Before Target Organ is ReachedInvolved Before Target Organ is Reached Origin Of The First Neuron Is The CNSOrigin Of The First Neuron Is The CNS

Origin of Neuron(Cell Body) No. 1

Parasympathetic Nervous Parasympathetic Nervous System,System,

(Or, Subdivision Of The(Or, Subdivision Of TheAutonomic Nervous Autonomic Nervous

System)System)

Parasympathetic Fibers Parasympathetic Fibers ExtendExtend ONLYONLY To The To The

Internal Organs—Internal Organs—Viscera- and eyes and Viscera- and eyes and

salivatory glands in head.salivatory glands in head.

PostganlionicNeuron

Preganglionic(Presynaptic)

Neuron(No. 1)

Postganglionic(Postsynaptic)

Neuron (No. 2)

Craniosacral Outflow

In or near organ supplied

L Colic Flexure

SACRALCORD

LEVELS

L Colic Flexure

BRAIN-STEM

C

O

P

S

COPS

BOTTOM LINEBOTTOM LINE

• (1) HOW MANY CRANIAL NERVES CARRY (1) HOW MANY CRANIAL NERVES CARRY PARASYMPATHETIC FIBERS?PARASYMPATHETIC FIBERS?

ANSWER: ANSWER: FourFour

(2) HOW MANY SPINAL NERVES CARRY (2) HOW MANY SPINAL NERVES CARRY • PARASYMPATHETIC FIBERS?PARASYMPATHETIC FIBERS?

ANSWER: ANSWER: ThreeThree

Sympathetic Nervous Sympathetic Nervous System,System,

(Or, Subdivision Of (Or, Subdivision Of The Autonomic The Autonomic

Nervous System)Nervous System)

ANS—Both Parasympathetic ANS—Both Parasympathetic &&

Sympathetic FibersSympathetic Fibers

• Target Organs Are Glands, Smooth Target Organs Are Glands, Smooth Muscle and Cardiac MuscleMuscle and Cardiac Muscle

Two Neurons Are Involved Before Target Two Neurons Are Involved Before Target

Organ is ReachedOrgan is Reached Origin Of The First Neuron Is The CNSOrigin Of The First Neuron Is The CNS

To Repeat what we said To Repeat what we said earlier,earlier,

BUT,BUT,Sympathetic Fibers Extend Sympathetic Fibers Extend

BothBoth To The Periphery To The Periphery (The Body Wall & Limbs) (The Body Wall & Limbs) AND AND to the Viscera, and to the Viscera, and therefore the Viscera are therefore the Viscera are

DuallyDuallyInnervated.Innervated.

PreganglionicNeuron

PostganlionicNeuron

Thoracolumbar Outflow

Origin and Distribution of Origin and Distribution of Sympathetic AxonsSympathetic Axons

• leave CNS ONLY between T1 & L2 leave CNS ONLY between T1 & L2 (thoracolumbar outflow). From (thoracolumbar outflow). From lateral horn cell bodies, pre-lateral horn cell bodies, pre-ganglionic axons pass into the ganglionic axons pass into the ventral root, spinal nerve,and ventral root, spinal nerve,and connect to the sympathetic trunk connect to the sympathetic trunk ganglia via white rami ganglia via white rami communicantes.communicantes.

Lateral Horn

WRC

Ventral Root

SympatheticTrunk Ganglion

Sp. N.

T1-L2

THENTHEN THE FIBERS, ONCE THE FIBERS, ONCE IN THE SYMPATHETIC IN THE SYMPATHETIC

TRUNK, MUST SYNAPSE TRUNK, MUST SYNAPSE IN EITHER :IN EITHER :

• The The ParavertebralParavertebral (Sympathetic Trunk) (Sympathetic Trunk) Ganglia OR,Ganglia OR,

• The The PrevertebralPrevertebral (Para-aortic) Ganglia (Para-aortic) Ganglia

SYMPATHETIC TR.WITH 2 CONNECTIONS TO SPINAL NERVES = RAMI COMMUNICANTES- White (lateral)& Gray (medial)

Paravertebral Ganglion(Sympathetic trunk Ganglion)

Lead to Prevertebral Ganglia

PREVERTEBRAL (OR)PREAORTIC

GANGLIAThese ganglia migrated

from paravertebral gangliaand dragged their presynaptic

G,L,& L splanchnic ns. with them.

(SYMP.)

Sympathetic Fibers Extend Sympathetic Fibers Extend BothBoth To The Periphery To The Periphery

(The Body Wall & Limbs) (The Body Wall & Limbs) AND AND to the Viscera, and to the Viscera, and

Therefore the Viscera are Therefore the Viscera are DuallyDually

Innervated.Innervated.

FundamentalsFundamentals

1) 31 pr. of spinal nerves supply the entire 1) 31 pr. of spinal nerves supply the entire surface of the body wall and limbs (recall surface of the body wall and limbs (recall

dermatomes)dermatomes) 2) Smooth muscle exists in every blood 2) Smooth muscle exists in every blood

vessel inferior to the cranial fossae and at the vessel inferior to the cranial fossae and at the basebase

of every hair follicle in the body.of every hair follicle in the body.3) Glands exist everywhere on the body 3) Glands exist everywhere on the body

surface.surface.

4)THEREFORE, SYMPATHETIC FIBERS 4)THEREFORE, SYMPATHETIC FIBERS REACH EVERY SQUARE INCH OF THE REACH EVERY SQUARE INCH OF THE

BODY SURFACE (PERIPHERY),BODY SURFACE (PERIPHERY),AND THEY ACCOMPLISH THIS BY AND THEY ACCOMPLISH THIS BY

COMMUNICATINGCOMMUNICATING WITH EVERY SPINAL NERVE WITH EVERY SPINAL NERVE

Big Picture Sympathetics:Big Picture Sympathetics:

1

2

• Sympathetic distribution – everywhere , both to the periphery (body wall and limbs) AND to the viscera

•All sympathetic fibers must enter sympathetic chain.

To go to the periphery , the fibers must extend from the symp. trunk

into EACH spinal nerve, by one of two means: either,

enter chain, then extend up/down, synapse and then follow GRC to spinal ns. at that level (which is a different level from that of the entry point—T1-L2)(Therefore), the only function of GRC is to carry postsynaptic fibers to every spinal nerve and therefore to the periphery (body wall and limbs).

• Sympathetic fibers use paravertebral chain (sympathetic chain) to

distribute both to (1) periphery and (2) viscera:

synapse in chain at same level, follow GRC to spinal n. or,

Implying they have to reach all spinal nerves (at, above, or below the level of entry)

TO THE PERIPHERY:

SPINAL N..

SPINAL N.

SPINAL N.

2

2

1

GRC

GRC

Origin

SYMPATHETICTRUNK

To Periphery below head

NOW, LET’S CONSIDER NOW, LET’S CONSIDER SYMPATHETIC FIBERS SYMPATHETIC FIBERS

TOTO THE HEAD THE HEAD

Sympathetic Trunk

Representing the smooth muscle & glands of head other than skin

ORIGINALLY, THERE WERE 8 CERVICAL SYMPATHETIC GANGLIA, ONE ASSOCIATED WITH EACH CERVICAL SPINAL NERVE. BUT, THESE GANGLIA COALESCED INTO 3 (4) GANGLIA. THEREFORE, THESE REMAINING CERVICAL SYMPATHETIC GANGLIA WERE LEFT TO SEND POSTSYNAPTIC FIBERS (VIA GRC) TO SEVERAL SPINAL NERVES EACH.

The sympathetic trunk is located posterior to the

carotid sheath on the prevertebral

fascia

K. Kryger

R. Common Carotid A

internal carotid a

I. Carotid npostgang. fibers

Superior Cervical Ganglion

(upper 4 ganglia)

Middle cervical ganglion

(ganglia 5 & 6)

Inferior cervical ganglion

(ganglia 7 & 8)

1st rib (cut)R. subclavian a. (cut)

hyoid

Ext. Carotid N.

Sympathetic fibers to the Head Sympathetic fibers to the Head would ascend as presynaptic would ascend as presynaptic

fibers to reach the most fibers to reach the most superior cervical sympathetic superior cervical sympathetic ganglion. Synapse would then ganglion. Synapse would then occur, and postsynaptic fibers occur, and postsynaptic fibers

would follow the arterial would follow the arterial branches (ECA & ICA) to reach branches (ECA & ICA) to reach the smooth muscle and glands the smooth muscle and glands of the head.Two large branches of the head.Two large branches (one, anyway) off the superior (one, anyway) off the superior

cervical ganglion are referred to cervical ganglion are referred to as the ECA and ICA nerves.as the ECA and ICA nerves.

The sympathetic trunk is located posterior to the

carotid sheath on the prevertebral

fascia

K. Kryger

R. Common Carotid A

internal carotid a

I. Carotid npostgang. fibers

Superior Cervical Ganglion

(upper 4 ganglia)

Ext. Carotid N.

Lateral horns of cord levels T1-2

superior cervical ganglion (in neck)

Target tissue

smooth muscle in vessel walls,

dilator pupillae m, & sweat glands.

Preganglionic axons ascendin the sympathetic trunk

Postganglionic axons distributed via Ext. & Int. carotid ns.( carotid plexus)

K. Kryger

Functions:

1) vasoconstriction

2) dilate pupils

3) stimulate sweat glandsPreganglionic fibres enter the

sympathetic trunk

Overview of Sympathetics to Overview of Sympathetics to HeadHead

Superior Cervical Ganglion

Sympathetic fibers to the head ascend in the sympathetic trunk and synapse in the superior cervical ganglion & then postganglionic fibers follow the ECA & ICA to reach the smooth muscle and glands of the head, including the eye.

Origin

NOW, LET’S CONSIDER NOW, LET’S CONSIDER SYMPATHETIC FIBERSSYMPATHETIC FIBERS

TO TO THETHE CERVICAL CERVICAL VISCERAVISCERA

Sympathetic fibers to the neck Sympathetic fibers to the neck viscera, eg. the pharynx, would viscera, eg. the pharynx, would ascend as presynaptic fibers to ascend as presynaptic fibers to reach the cervical sympathetic reach the cervical sympathetic ganglia. Synapse would then ganglia. Synapse would then

occur, and postsynaptic fibers occur, and postsynaptic fibers wouldwould

pass to the viscera via direct pass to the viscera via direct branches or via the blood vessels.branches or via the blood vessels.

Cervical Viscera

Origin

THE ENDTHE END