AUTONOMIC NERVOUS SYSTEM
Gabriel Lo Hinolan MD
Autonomic Nervous System
" Part of Peripheral Nervous System:
" Visceral/splanchnic component of Nervous System
" Major difference compared with somatic component
– Visceral efferent pathway is interrupted by peripheral synapses, at least 2 neurons interposed between CNS and visceral effectors
1. VISCERAL EFFERENT PATHWAY
" Somata located in visceral efferent muscles of cranial nerves and spinal lateral gray columns;
" Axons are finely myelinated traverse the cranial and spinal nerves to the peripheral ganglia where they synapse with dendrites of somata of secondary neurons.
" Axons are non-striated muscle or glandular cells, adipose cells, mast cells, melanocytes, interstitial cells, autonomic ganglia and motor end plates.
· Preganglionic Neurons
· Postganglionic Neurons-more numerous
o 1:15-20 -average synapses
o Allows wide diffusion of many automatic effects.
o This disproportion is greater in sympathetic parts of A.N.S.
2. VISCERAL AFFERENT Pathway
" resemble somatic afferent
" Their peripheral fibers originate in the cranial & dorsal root ganglias as unipolar Cells/Neurons
" Their peripheral fibers are distributed through autonomic ganglia or plexuses.
" Their central Fibers/Axons accompany somatic efferent fibers through dorsal spinal roots to the CNS
3 Major Parts of Autonomic Nervous System
1. Parasympathetic - Craniosacral Flow
2. Sympathetic - Thoracolumbar Flow
· The somata of their postganglionic muscles are peripheral as discrete ganglia near to the structure innervated or in the walls of viscera.
· The somata of their Postganglionic neurons are located mostly in ganglia of sympathetic trunks.
· Ganglionated plexuses in the wall of G.I.T.
· Contains reflex pathway for contraction of Alimentary tracts, secretions of Gastric Acid, Transport of water & electrolytes and mucosal blood Flow.
Mechanism of Transmission
1. Traditional / Old Theory
o Cholinergic Activity
o Conserves Body Energy
o Adrenergic Activity
o Mobilize Body Energy
2. New Advances (1960’s)
A. NANC- “Purinergic”
o Non- Adrenergic & non-Cholinergic nerves
o ATP (neurotransmitter)
B. Co- transmission
o That most nerves release more than one
§ Sympathetic - ATP, NPY
§ Parasympathetic - Ach, N.O., V.I.P., ATP
§ Sensory & Motor Nerves - SP, CGRP, ATP
§ Enteric - NANC Inhibitory nerves - ATP, VIP, N.O. as co- transmitter
§ Enteric excitatory nerves- Ach, SP.
o The concept that locally released agents can alter neurotransmission either by pre-junctional modulation. E.g. Autoinhibition, Cross-talk, Synergism, Opposite Actions, Prolongation of effect, Trophic effects
D. Sensory-motor nerves
o some primary different nerves fibers that release neurotransmitter from their peripheral endings during “axon reflex”
E. Intrinsic circuitry
o That many “Intrinsic Ganglia” contain integrative circuits capable of modulating sophisticated local activities. E.g. Aorta, Bladder, Trachea.
o Main reason why transplanted organs are not denervated.
F. Autonomic Neuromuscular Junctions
o That the A.N.S. Neuromuscular junctions differ in several important ways from Skeletal Neuromuscular Junction and also from the synapses in the CNS and PNS.
o Gap Junctions/Muscle Bundle (Visceral Nerves)
o Single cells (Somatic Nerves)
o Changes in the expression of neurotransmitters and receptors in the mature adult in response to hormones and growth factors of the ff: Trauma, surgery.
** Rate of Diseases, chronic drug treatment Degeneration of A.N.S. differs according to regions and type of fibers.
A.) Raynauds disease - removal of sympathetic trunk or pre-ganglionic fibers to alleviate vascular spasm.
B.) Hypertension- Sypathectomy of Bilateral trunks T8-L1
C.) Severe Angina Pectoris-Sympathectony to relieve pain.
D.) Dysmenorrhea- Removal of superior hypogastric plexus.
E.) Loss of Ejaculation & Sterility - due to resection of sup. Hypogastric plexus.
PARASYMPATHETIC NERVOUS SYSTEM
· Are myelinated and found in the ff.
o Accessory cranial nerves
o 2nd and 4th sacral nerves.
4 Small peripheral ganglias in the Cranial Part
· Are non-myelinated and shorter
1. Oculomotor Nerve
· Accessory oculomotor nuclei (Edinger-Westphal) in the midbrain.
· Synapse with postganglionic fibers at the ciliary ganglion to innervate the ciliary muscle & sphincter pupillae.
2. Facial Nerve
· Superior salivatory nucleus in the medulla.
· Passes above the Stylomastoid Foramen
· Synapse with Pterygopalatine ganglion to innervate the Lacrinal Gland, Nasal and Palatal Glands via the Zygomatic nerve
· Synapse with submandibular ganglion to innervate the submandibular & Sublingual glands via d lingual nerve
3. Glossophayngeal Nerve
· Inferior salivatory nucleus in the medulla
· synapse with otic ganglion to innervate the parotid gland via the auriculotemporal nerve.
4. Vagus Nerve
· Dorsal Nucleus in the medulla.
· Synapse with postganglionic fibers in the walls of the organs they innervate thru its numerous branches: Pulmonary, cardiac, esophageal, gastric, intestinal, hepatic, Pancreatic, & Renal.
5. Anterior Rami of S2, S3, & S4 Spinal Nerves
· Synapse with postganglionic fibers w/in the walls or adjacent to the organs (sexual organs, external genitelia, Large intestine, Urinary Bladder) they innervate.
· Excitatory to Rectum & Bladder walls
· Inhibitory to vasical sphincter, vasodilator to penile & clitoral tissue, testes and ovaries, uterine tubes and uterus.
SYMPHATHETIC NERVOUS SYSTEM
" Contain two ganglionated trunks & their branches, plexuses and subsidiary ganglia.
· are myelinated and found in the Lateral gray column of all thoracic & L1 L2 & L3 segments
Course: Begins at the Lateral Grey Column then passes thru the Ventral Spinal Roots into the spinal Nerves thru its Ventral Rami Communicants to join their corresponding ganglia in the sympathetic trunks or their interganglionic segments.
3 behaviors of the Preganglionic Fibers at the Sympathetic Trunks:
· Synapse with neurons in the nearest ganglion.
· They may traverse that ganglion to end in another ganglion.
· They may traverse that ganglion to synapse in one of the automatic plexuses. E.g. celiac & mesenteric Arteries
“Nervi Terminals” - postal extension of sympathetic system with efferent postganglionic fibers to the blood vessels & glands of nasal cavity.
“Sympathetic Ganglia”- Collection of cells on the sympathetic trunks, autonomic plexuses & intermediate ganglia.
Differentiating characters with Parasympathetic Ganglia:
1. Multiple Synapse of pre-ganglionic fibers
2. Mediation of interneurons
3. Diffusion w/in the ganglion of transmittee substance locally produced (Paracrine effect) or produced elsewhere (Endocrine effect.).
· Axons are non-myelinated and narrow.
Distribution to effector organs:
1. Thru the Gray Rami Communicants.
2. Thru medial Branch of a Ganglion.
3. Via the blood vessels to their peripheral distribution
4. May ascend or descend before leaving the sympathetic trunk.
Peripheral autonomic activity is integrated at higher levels in the ff:
o Reticular formation
o Limbic lobe
o Prefrontal neocortex
“Sympathetic trunk” -- 2 ganglionated irregular nerve cords from the cranial base to the coccyx.
Neck à Anterior to cervical transverse process posterior to Carotid sheath
Thorax à Anterior to the head of the ribs
Abdomen à Anterolateral to the lumbar vertebral bodies
Pelvis à Anterior to the sacrum; medial to anterior sacral foramina
Coccyx à fuse to become “Ganglion Impar”
I. Cranial Part of the Sympathetic System
- Begins on each side as internal carotid nerve a branch of Superior Cervical Ganglion containing the postganglionic fibers. Ascending behind the interval carotid artery it divide into a smaller medial branch and a larger lateral branch w/c contribute to the internal carotid plexus.
Internal Carotid Plexus
- Contains a small Medial carotid Ganglion.
Laterally it communicates with the ff:
1. Trigeminal Ganglia
2. Pterygopalatine Ganglia via the deep Petrosal Nerve
3. Abducent Nerve
4. Tympanic branch of Glosspharyngeal Nerve via the Superior & Inferior Caroticotympanic nerves.
Medially it gives off the ff. Branches:
1. Branch to the Internal Carotid artery
2. Oculomotor Branch
3. Trochlear Branch
4. Ophthalmic Branch
5. Abducent branch
6. Ciliary Ganglion
7. Hypophysis Cerebri
II. Cervical Part of the Sympathetic System
- Send gray rami communicate to the cervical spinal nerve.
- Preganglionic fibers pass via the white rami communicate of the upper thoracic spinal nerve.
A. Superior Cervical Ganglion
· Largest; formed by the fused C1-C4 ganglia; adjoins the c2 & c3 vertebral.
Anterior - Internal Carotid Artery
Posterior - Longus Capiti Muscle
1. Lateral Branch
- Are the gray communicate to the upper C1-C4 spinal nerve & to some cranial nerves.
- Jugular nerve - forms the superior & Inferior Vasal Ganglion
2. Medial Branch
- supplies the carotid body
- Descends behind the common carotid artery and anterior to the Inferior Thyroid artery and Recurrent Laryngeal Nerve.
A. Right Cardiac Branch
- Passes behind the subclavian, Brachiocephalic trunk, Arch of Aorta where it joins Deep Cardiac Plexus.
- Communicates with External Laryngeal Nerve, recurrent larngeal nerve, vagal nerve end, thyroid branches of the middle cervical ganglion
B. Left Cardiaaaac Branch
- Pass anterior to the left common carotid aortic arch. To end in the deep cardiac plexus
- Communicates with cardiac branches of Middle Cervical ganglion, cervicothoracic sympathetic ganglia and inferior branches of left vagus.
3. Anterior Branch
- Ramify on the common and external carotid arteries.
- Plexus on the Facial artery communicates with the submandibular ganglion
- Plexus on the Middle Meningeal Artery comminicates with the Facial and otic ganglion thru the ext. petrosal nerve
B. Middle Cervical Ganglion
- Smallest; found at the level of C6 antero superior to the inferior thyroid artery
- may join the Cervicothoracic ganglion
- formed by the ganglia of C5 and C6
1. Thyroid Branch
- accompanies inferior thyroid artery
- communicates with external laryngeal nerve, recurrent laryngeal nerve and superior cardiac nerve
- supplies thyroid and parathyroid gland
2. Cardiac Branch
- Largest sympathetic nerve
- Descends behind the common carotid artery an in front of the subclavian artery, receives branches of recurrent laryngeal nerve before it ends at the Deep Cardiac Plexus.
- Between the left common carotid and subclavian arteries before it ends at the Deep Cardiac Plexus
C. Cervicothoracic (Stellate ganglion; inferior)
- Irregularly shaped
- formed by the fusion of lower to cervical ganglion and 1st thoracic ganglion
- lateral to the lateral border of longus coli
“ANSA SUBCLAVIA” - connects the middle cervical ganglion to the cervicothoracic ganglion.
A. CARDIAC BRANCH
- Passes behind the subclavian artery and anterior to the trachea before it communicates with recurrent laryngeal nerve and cardiac branch of middle cervical ganglion before it ends in the deep cardiac plexus.
B. BRANCHES TO THE BLOOD VESSELS
- forms plexuses on the subclavian artery vertebral artery, inferior thyroid artery
Preganglionic Fibers to Head & Neck - emerge from the upper five thoracic spinal nerves
Preganglionic Fibers to Upper Limb - emerge from T2-T6
III. Thoracic Part of the Sympathetic System
- 11, 12, 10 or 13
1st Thoracic Ganglia - Fused with Inferior Cervical ganglion to form the Cervicothoracic Ganglion
- Sometimes include Middle Cervical Ganglion and 2nd Thoracic Ganglion.
- Lies against the costal Heads, posterior to the costal Pleura.
- Lowest two ganglia lie lateral to the bodies of corresponding vertebrae.
- Passes dorsal to medial accurate ligament or crus of diaphragm to become lumbar part.
1. Thoracic Aorta Plexus - medial branches of upper five ganglia.
2. Splanchnic Nerves - medial branches of lower seven ganglia.
· Greater Splanchnic Nerve - branches of 5th to 9th or 10th ganglia.
· Lesser Splanchnic Nerve - branches of 9th & 10th or 11th ganglia.
· Lowest Splanchnic Nerve (Renal Nerve) - Branch of lowest thoracic ganglion.
IV. Lumbar Part of the Sympathetic Trunk
- 4 ganglia; extraperitoneal.
- Anterior to vertebral column and medial to the Psoas muscle.
- Superiorly communicates with thoracic Part & inferiorly becomes Pelvic Part passing posterior to common Iliac artery. To the left the Lat. Aortic L.N., to the right, is the Inferior Vena Cava.
1st Lumbar Splanchnic Nerve (1st Ganglion)
- Joins the coeliac, renal & intermesenteric Plexuses.
2nd Lumbar Splanchnic Nerve (2nd or 3rd Ganglion)
- Inferior part of intermesenteric plexus.
3rd Lumbar Splanchnic Nerve (3rd or 4th Ganglion)
- Joins superior hypogastric plexus.
4th Lumbar Splanchnic Nerve (Lowest Ganglion)
- Joins the lowest part of sup. Hypogastric plexus
- joins the aortic plexus
- reaches up to the Femoral Artery
V. Pelvic part of the Sympathetic System
- 4 or 5 Ganglia
- Anterior to the sacrum, antero-medial to the anterior Sacral Foramina.
- Superiorly communicates with lumbar part and inferiorly end anterior to the coccyxas “Ganglion Impar”
- 1st 2 Ganglia - joins the Inferior hypogastric (Pelvic) Plexus
- Forms plexuses/ branches to the Popliteal, Pudendal, Superior and Inferior Gluteal Nerves.
VI. Plexuses in the Thoracic, Abdominal & Pelvic Cavities
- Pass along most branches of the large vessels which they surround and are usually named after the artery along which they are distributed.
1. CARDIAC PLEXUSES
A. Superficial (Ventral) Cardiac Plexus
- below the aortic arch and anterior to the right pulmonary artery
- Formed by the cardiac branch of left superior cervical sympathetic ganglion and the lower of the two cervical cardiac branches of the left vagus.
- A small cardiac ganglion
- connects with the following:
- deep cardiac plexus
- right coronary plexus
- left anterior pulmonary plexus
B. Deep (dorsal) Cardiac Plexus
- Posterior to the aortic arch; anterior to the tracheal Bifurcation
- formed by:
1. Cardiac branches of Cervical and upper thoracic sympathetic ganglia
2. Vagus Nerve
3. Recurrent Laryngeal Nerves
1. Right Half - forms part of right coronary plexus
2. Left Half - forms much of left coronary plexus
C. Left Coronary Plexus
- Formed by left half and a few fibers from right half
- Accompanies the left coronary artery to supply the left atruim and venticle
D. Right Coronary Plexus
- Formed by both the superficial and deep plexuses
- accompanies the right coronary artery to supply the right atrium and ventricle
E. Atrial Plexus
- Overlaps the fibers of right and left coronary plexuses to supply the atria
- All cardiac branches of the vagus and sympathetic trunk contain both afferent and efferent fibers except the cardiac branch of superior cervical ganglion which is purely efferent.
2. Pulmonary Plexuses
- Located anterior and posterior to the other hilar structures of the lump.
Anterior pulmonary plexus
- Formed by rami of vagus and cervical sympathetic cardiac nerves
Posterior Pulmonary Plexus
- Formed by rami of vagus and thoracic sympathetic ganglia (T2-T6)
3. Coeliac Plexuses
- Largest Autonomic Plexus; T12 – L1
- Surrounds the coeliac artery and superior mesenteric artery
- Posterior to stomach
- Anterior to cruca of diaphragm, abdomial aorta, suprarenal glands
- Joined by greater and lesser splanchnic nerves vagus and phrenic nerves
- Irregular masses on each side bet. The suprarenal gland.
- RIGHT à Behind the Inferior Vena Cava
- LEFT à Behind the Splenic vessels
1. Phrenic Plexus
- Accompanies inferior phrenic artery to the diaphragm
- Larger on the right; phrenic ganglion
2. Hepatic Plexus
- Largest, connets with right Phrenic Nerve left and right vagus.
- Accompanies hepatic artery and portal vein to the liver, gallbladder (CYSTIC PLEXUS) and bile ducts.
3. Left Gastric Plexus
- Accompanies left gastric artery along the lesser curvature
4. Spleenic Plexus
- Accompanies spleenic artery to the splenic capsule
5. Suprarenal Plexus
- Formed by coeliac plexus and greater splanchnic nerve.
6. Renal Plexus
- Formed by coeliac plexus, aorticornenal ganglion, lowest thoracic splanchnic nerve and oartic plexus
- Accompanies renal artery to supply the vessels, renal glomeruli and tubules
- Gives off uretic pelxus which supplies the ureters
7. Testicular plexus
- Accompanies testicular artery to the testes, via the epididymis and ductus deferens.
8. Ovarian Plexus
- Accompanies ovarian artery to the ovary and uterine tubes
9. Superior Mesenteric Plexus
- Accompanies the superior mesenteric artery to the mesentery where it further subdivides into the branches of sup. Mesenteric artery
- Superior mesenteric ganglion
10. Abdominal Aortic Plexus (Intermesenteric)
- Formed by coeliac plexus and L1 to L2 splanchnic nerves
- Located anterior and lateral to the abdominal aorta, between the superior and inferior mesenteric artery origins.
- Supplies the inferior vena cava.
11. Inferior Mesenteric Plexus
- From aortic plexus and L2 Splanchnic nerves
- Accompanies Inferior mesentery artery and distributed along its branches.
- Inferior Mesenteric ganglion
4. Superior Hypogastric Plexus (Pre-Sacral Nerve)
- Anterior to aortic bifurcation, left common Iliac vein, medial sacral vessels, L5 vertebral body and sacral promontory.
- Between the common iliac arteries
- From aortic plexus and L3 and L4 splanchnic nerves.
- Left and right branches supplying branches to ureteric, ovarian, testicular, and common iliac plexuses
5. Inferior Hypogastric Plexus (Pelvic)
- From the superior hypogastric plexus and pelvic splanchnic nerves
- Located medial to each internal iliac artery and posterior to sacral and coccygeal plexuses.
- Supplying branches to ureteric, ovarian, testicular, internal iliac plexus and sigmoid colon
MALE: Lateral to: rectum, seminal vesicle, prostate, post. Of urinary bladder.
FEMALE: Lateral to: rectum, uterine cervix, vaginal fornix, post. Of urinary bladder.
1. Middle Rectal Plexus
- From inferior hypogastric plexus
- Accompanies middle rectal artery to supply rectum and anus (internal and sphincter) Inferior Rectal Nerve – supplies external anal sphincter
NERVE SUPPLY TO RECTUM & ANAL CANAL
- Superior Rectal Plexus
- Middle Rectal Plexus
- Inferior Rectal Plexus (Haemorrhoidal Nerve – branch of pudendal nerve)
2. Vesical Plexus
- Accompanies vesical arteries to the bladder with branches to seminal vesicles and ductus deferens
3. Prostatic Plexus
- Supplies: prostate, seminal vesicles, prostatic urethra, ejaculatory ducts, corpora cavernosa, corpora spongiosum, membranous and prcile urethra and bulbo-urethral glands.
- Greater and lesser cavernous nerve
4. Ureterovaginal plexus
- Accompanies uterine arteries in broad ligament.
UTERINE NERVE – uterine ganglion
VAGINAL NERVE – vaginal wall, clitoris, urethra, greater vestibular glands
ENTERIC NERVOUS SYSTEM
- Arise form neural crest
- System of neurons found within the walls of the Gastrointestinal tract
- 10 to 100 million neurons
- Intrinsic Plexus
- Extrinsic Nerve Supply
Myenteric or Auerbach’s Plexus
- Lies between the longitudinal and circular musculocoats
- From the oral esophagus to internal anal sphincter
Submucous or Meissner’s or Henle’s Plexus
- Lies between the circular muscle layer and muscularis mucosae.
- Form the stomach to internal anal sphincter.
- Smaller meshes; bigger ganglia; finer strands
- Contains more neurons
Extrinsic Nerve Supply
- Postgangliodnated sympathetic fivers form coeliac and superior and inferior mesenteric ganglia
- Preganglionic fibers from Pelvic and vagus nerves.
- “unusual autonomy in that it retains many functions after all central connections are severed.”
E.g. Peristalsis reflex
Enteric excitatory motor neurons
- Use acetylcholine and substance P as co-transmitters.
Enteric Inhibitory Motor Neurons
- Uses ATP, VIP, N.O.
ATP – dominant in small intestine and colon
VIP – dominant in stomach
Sensory And Sensory-Motor Nerves
- Accompanies the efferent autonomic fibers to the viscera and blood vessels = General Visceral or autonomic afferent fibers
- Segmental arrangement
- Unipolar neurons
- Mediate organic visceral sensatory like: hunger, nausea, sexual excitement, vesical distension, cough, reflexes, etc.
- Responsible for visceral and referred pain in the abdomen.
- Distributed in: vagal, glossopharyngeal, s2-s4 sacral nerves thru pelvic splanchnic nerves, thoracic and upper lumbar spinal nerves thru rami communicants.