DENTAL & OPTOMETRY STUDENTS

INTRODUCTION TO AUTONOMIC NERVOUS SYSTEM— IE, SOMATIC NERVOUS SYSTEM VERSUS AUTONOMIC NERVOUS SYSTEM GEORGE SALTER, PH.D DENTAL STUDENTS

The Motor Aspect Of The Nervous System May Be Divided Into A Somatic Part And An Autonomic Part

SOMATIC NERVOUS SYSTEM TARGET ORGAN IS SKELETAL MUSCLE A SINGLE NEURON IS INVOLVED THE ORIGIN OF THE SINGLE NEURON IS THE CNS, SPECIFICALLY THE ANTERIOR HORN CELLS

Thoracic Cord PH LH AH Anterior Horn Cell

AUTONOMIC NERVOUS SYSTEM

Functionally, The Autonomic Nervous System May Be Divided Into A Sympathetic Part And A Parasympathetic Part. These Two “Divisions” Have Opposite Effects—Eg. Sympathetic Fibers Increase The Heart Rate (Tachycardia) And The Parasympathetic Fibers Decrease The Pulse (Bradycardia).

ANS—Both Parasympathetic & Sympathetic Fibers Target Organs Are Glands, Smooth Muscle and Cardiac Muscle Two Neurons, And Thus a Synapse, Are Involved Before Target Organ is Reached Origin Of The First Neuron Is The CNS

Origin of Neuron (Cell Body) No. 1

Parasympathetic Nervous System, (Or, Subdivision Of The Autonomic Nervous System)

Parasympathetic Fibers Extend ONLY To The Internal Organs— Viscera- and eyes and salivatory glands in head.

Craniosacral Outflow Postganlionic Neuron Postganglionic (Postsynaptic) Neuron (No. 2) Preganglionic (Presynaptic) Neuron (No. 1) Craniosacral Outflow

In or near organ supplied

L Colic Flexure SACRAL CORD LEVELS

S C P BRAIN- STEM O COPS L Colic Flexure

BOTTOM LINE (1) HOW MANY CRANIAL NERVES CARRY PARASYMPATHETIC FIBERS? ANSWER: Four (2) HOW MANY SPINAL NERVES CARRY PARASYMPATHETIC FIBERS? ANSWER: Three

Sympathetic Nervous System, (Or, Subdivision Of The Autonomic Nervous System)

ANS—Both Parasympathetic & Sympathetic Fibers To Repeat what we said earlier, ANS—Both Parasympathetic & Sympathetic Fibers Target Organs Are Glands, Smooth Muscle and Cardiac Muscle Two Neurons Are Involved Before Target Organ is Reached Origin Of The First Neuron Is The CNS

BUT, Sympathetic Fibers Extend Both To The Periphery (The Body Wall & Limbs) AND to the Viscera, and therefore the Viscera are Dually Innervated.

Thoracolumbar Outflow Preganglionic Neuron Postganlionic Neuron Thoracolumbar Outflow

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

Lateral Horn T1-L2 Sp. N. Ventral Root Sympathetic Trunk Ganglion WRC

THEN THE FIBERS, ONCE IN THE SYMPATHETIC TRUNK, MUST SYNAPSE IN EITHER : The Paravertebral (Sympathetic Trunk) Ganglia OR, The Prevertebral (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

These ganglia migrated from paravertebral ganglia (SYMP.) PREVERTEBRAL (OR) PREAORTIC GANGLIA These ganglia migrated from paravertebral ganglia and dragged their presynaptic G,L,& L splanchnic ns. with them.

Sympathetic Fibers Extend Both To The Periphery (The Body Wall & Limbs) AND to the Viscera, and Therefore the Viscera are Dually Innervated.

Fundamentals 1) 31 pr. of spinal nerves supply the entire surface of the body wall and limbs (recall dermatomes) 2) Smooth muscle exists in every blood vessel inferior to the cranial fossae and at the base of every hair follicle in the body. 3) Glands exist everywhere on the body surface. 4)THEREFORE, SYMPATHETIC FIBERS REACH EVERY SQUARE INCH OF THE BODY SURFACE (PERIPHERY), AND THEY ACCOMPLISH THIS BY COMMUNICATING WITH EVERY SPINAL NERVE

Big Picture Sympathetics: Sympathetic distribution – everywhere , both to the periphery (body wall and limbs) AND to the viscera All sympathetic fibers must enter sympathetic chain. Sympathetic fibers use paravertebral chain (sympathetic chain) to distribute both to (1) periphery and (2) viscera: To go to the periphery , the fibers must extend from the symp. trunk into EACH spinal nerve, by one of two means: either, synapse in chain at same level, follow GRC to spinal n. or, 1 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). 2

SPINAL N. 2 SPINAL N.. 2 TO THE PERIPHERY: Implying they have to reach all spinal nerves (at, above, or below the level of entry) SPINAL N. 2 GRC SPINAL N.. Origin 1 SPINAL N. 2 GRC

To Periphery below head SYMPATHETIC TRUNK

NOW, LET’S CONSIDER SYMPATHETIC FIBERS TO THE HEAD

Representing the smooth muscle & glands of head other than skin Sympathetic Trunk

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.

I. Carotid n postgang. fibers The sympathetic trunk is located posterior to the carotid sheath on the prevertebral fascia Superior Cervical Ganglion (upper 4 ganglia) Ext. Carotid N. internal carotid a hyoid Middle cervical ganglion (ganglia 5 & 6) Superior cervical ganglion – found at the levels of C2&3 vertebrae Middle cervical ganglion – found at C6 vertebra Inferior cervical ganglion – found between the base of the TP of C7 vertebra & neck of the 1st rib Inferior cervical ganglion (ganglia 7 & 8) R. Common Carotid A 1st rib (cut) R. subclavian a. (cut) K. Kryger

Sympathetic fibers to the Head would ascend as presynaptic fibers to reach the most superior cervical sympathetic ganglion. Synapse would then occur, and postsynaptic fibers would follow the arterial branches (ECA & ICA) to reach the smooth muscle and glands of the head.Two large branches (one, anyway) off the superior cervical ganglion are referred to as the ECA and ICA nerves.

I. Carotid n postgang. fibers The sympathetic trunk is located posterior to the carotid sheath on the prevertebral fascia Superior Cervical Ganglion (upper 4 ganglia) Ext. Carotid N. internal carotid a Superior cervical ganglion – found at the levels of C2&3 vertebrae Middle cervical ganglion – found at C6 vertebra Inferior cervical ganglion – found between the base of the TP of C7 vertebra & neck of the 1st rib R. Common Carotid A K. Kryger

Overview of Sympathetics to Head Postganglionic axons distributed via Ext. & Int. carotid ns.( carotid plexus) Target tissue smooth muscle in vessel walls, dilator pupillae m, & sweat glands. superior cervical ganglion (in neck) Preganglionic axons ascend in the sympathetic trunk Functions: 1) vasoconstriction 2) dilate pupils 3) stimulate sweat glands Preganglionic fibres enter the sympathetic trunk Lateral horns of cord levels T1-2 K. Kryger

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. Superior Cervical Ganglion Origin

NOW, LET’S CONSIDER SYMPATHETIC FIBERS TO THE CERVICAL VISCERA

Sympathetic fibers to the neck viscera, eg Sympathetic fibers to the neck viscera, eg. the pharynx, would ascend as presynaptic fibers to reach the cervical sympathetic ganglia. Synapse would then occur, and postsynaptic fibers would pass to the viscera via direct branches or via the blood vessels.

Cervical Viscera Origin

THE END