Autonomic Nervous System (2026) PDF

UNIVERSITY OF NORTHERN PHILIPPINES NEUROSCIENCE 1A LC18 AUTONOMIC NERVOUS SYSTEM COLLEGE OF M...

UNIVERSITY OF NORTHERN PHILIPPINES NEUROSCIENCE 1A LC18 AUTONOMIC NERVOUS SYSTEM COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Sto. Domingo, Sulit, Viloria Dr. Crispin Allan Viado | January 2023 Editors: Sudayon, Tan OUTLINE I. INTRODUCTION TO AUTONOMIC NERVOUS SYSTEM A. Differentiation Between Somatic & Autonomic Nervous System B. Comparison Between Somatic & Nervous System C. Autonomic Nervous System D. Subdivisions of Autonomic Nervous System E. Video: Autonomic Nervous System - Introduction (Anatomy Zone) II. SYMPATHETIC DIVISION A. Sympathetic Division B. Sympathetic Chain Ganglia (PARAVERTEBRAL GANGLIA) Figure 2. Autonomic nervous system C. Collateral Ganglia D. Specialized Neuron **Somatic Neurons - Heavily Myelinated, Autonomic- Thinly Myelinated E. Three Pathways of the Sympathetic Ganglia **The final common pathway linking CNS and Skeletal muscle is the Alpha motor F. Adrenal Medulla or the Adrenal Gland neuron while in the autonomic NS, the final common pathway to the visceral are G. Summary of Sympathetic Division the sympathetic and the parasympathetic neurons. H. Sympathetic Nervous System - Basic Configuration (From Supplementary Video) I. Sympathetic Nervous System - Distribution (From Supplementary Video) III. PARASYMPATHETIC DIVISION Figure 3. Somatic Nervous System Neuron A. Parasympathetic Outflow B. Organization and Anatomy of the Parasympathetic Division C. Functions of the Parasympathetic Division D. Parasympathetic Activation and Neurotransmitter Release E. Summary of the Parasympathetic Division F. Supplementary Video: Parasympathetic Nervous System Figure 4. Autonomic Nervous System Neuron I. INTRODUCTION TO AUTONOMIC NERVOUS SYSTEM A. DIFFERENTIATION BETWEEN SOMATIC AND AUTONOMIC SYSTEM Figure 5. Somatic Nervous System **SOMATIC NS: Acetylcholine is the main neurotransmitter (cholinergic) and is a single neuron pathway. Neurons are heavily myelinated. Figure 6. Autonomic Nervous System Neuron Pathway **Preganglionic - Thin myelin, Postganglionic - No myelin Figure 1. Nervous System AUTONOMIC NS: **Autonomic nervous system is a general visceral motor division of the Ventral horn is involved that will give rise to the ventral root and goes peripheral nervous system. It is distinct from the general somatic motor division to the peripheral nerve which is myelinated and synapses in the which innervates the skeletal muscles. neuromuscular junction with the skeletal muscle through the acetylcholine receptors. Chain of 2 motor neuron First is the Preganglionic neuron, its axon/fiber synapses with the second motor neuron (postganglionic neuron) in the peripheral ganglia (cell bodies in PNS). Postganglionic axon/fiber therefore extends to the visceral or effector organ. Functionally, preganglionic neurons signal the postganglionic neuron. Then the postganglionic neuron will stimulate the gland/effector Page 1 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO organ. Axons of preganglionic neurons are thinly myelinated and has slower conduction; Postganglionic neurons are unmyelinated and has even slower conduction. Autonomic ganglia are motor ganglia containing cell bodies of motor neurons; in contrast dorsal ganglia which is sensory ganglia B. COMPARISON BETWEEN SOMATIC AND AUTONOMIC SYSTEM Figure 6. Role of Autonomic Division in Homeostasis AUTONOMIC (SELF-GOVERNING) Part of the Peripheral nervous system Responsible for regulating involuntary body functions - Such as heartbeat, blood flow, breathing and digestion - A.k.a. VISCERAL or INVOLUNTARY NERVOUS SYSTEM Function outside of our conscious awareness (INVOLUNTARY) - no involvement of cerebral cortex Makes routine adjustments in our body’s systems(homeostasis) see figure - Regulates body temperature - Coordinates cardiovascular, respiratory,digestive, excretory and reproductive functions **Sympathetic NS has a direct innervation to the adrenal medulla which secretes Together with the endocrine system, control the internal Epinephrine (Adrenaline) and Norepinephrine (Noradrenaline) to the blood environment of the body. vessels and acts as hormones. Consists of an Afferent, connector and efferent neuron Rapid control Widespread (since one preganglionic axon may synapse with several postganglionic neurons) Divided into two parts ○ Sympathetic and Parasympathetic D. SUBDIVISIONS OF AUTONOMIC NERVOUS SYSTEM Figure 7. Autonomic Innervation of Sympathetic and Parasympathetic NS C. AUTONOMIC NERVOUS SYSTEM Page 2 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO 1. SYMPATHETIC NERVOUS SYSTEM The sympathetic system is the larger of the two parts of the autonomic system and is widely distributed throughout the body, innervating the heart and lungs, the muscle in the walls of many blood vessels, the hair follicles and the sweat glands, and many abdominopelvic viscera. AKA THORACOLUMBAR DIVISION Fight, flight or fright Activated during exercise, excitement and emergencies All preganglionic fibers release ACETYLCHOLINE. The effects are STIMULATORY. Most postganglionic fibers release NOREPINEPHRINE. The effects are STIMULATORY. **The somatic nervous system - peripheral stimulus being picked up by a sensory Not all postganglionic fiber in the sympathetic division is receptor and this peripheral stimulus gets brought back into the central nervous ADRENERGIC (RELEASE EPINEPHRINE) system by the sensory neuron. ○ Those that INNERVATE the SWEAT GLANDS and BLOOD The sensory neuron has the cell bodies in the dorsal root ganglion and VESSELS in skeletal muscle are CHOLINERGIC (RELEASE the pseudo unipolar neuron passes via the dorsal root into the dorsal ACh) aspect of the spinal cord and these sensory fibers ascend to the brain via the dorsal columns or the anterolateral system. The spinothalamic 2. PARASYMPATHETIC NERVOUS SYSTEM tract in which case they would cross over and ascend. The activities of the parasympathetic part of the autonomic system are directed The motor component of the somatic nervous system originates in the toward conserving and restoring energy. ventral horn of the spinal cord in the gray matter, and it leaves this ventral root and then it has this single neuron which innervates the skeletal muscle and results in contraction. There's one single neuron AKA CRANIOSACRAL DIVISION in the efferent component of the somatic nervous system which Rest and digest extends from the central nervous system to the periphery. Concerned with conserving energy All preganglionic fibers release ACETYLCHOLINE. The effects are STIMULATORY. Postganglionic fibers release ACETYLCHOLINE but the effects can be INHIBITORY ** Very long preganglionic fibers, but very short postganglionic fibers which are close to or within the target organ. E. VIDEO: AUTONOMIC NERVOUS SYSTEM - INTRODUCTION (Anatomy Zone) **Autonomic Nervous System consists of two main divisions Parasympathetic NS Sympathetic NS **Two Sets of Neurons between the CNS and the PNS in the Autonomic Nervous System PREGANGLIONIC NEURON - neuron before the autonomic ganglion - cell bodies are located in the spinal cord or brain - axons are myelinated - relatively short in length (sympathetic nervous system) - has a longer distance to travel in order to form this synapse with the postganglionic neuron (parasympathetic nervous system) POSTGANGLIONIC NEURON - extends to the target organ - location might be in the sympathetic chain in the paravertebral **The sympathetic outflow originates in the Thorax to Lumbar regions of the ganglia, or in parasympathetic NS (in or near the target organs) spinal cord so this extends from spinal segments T1 to L2 - axons are unmyelinated relatively long in length (sympathetic Nervous system) **The parasympathetic nervous system referred to as cranio-sacral (cranial nerve - relatively shorter (parasympathetic nervous system) components & sacral components) Cranial nerves components: CN III, VII, IX, X Sacral components: sacral regions S2 & S4 Page 3 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO gluconeogenesis, lipolysis) In terms of the bladder, the detrusor muscle relaxes and sphincter contracts Role in Male genitalia: ejaculation SHOOT/EJACULATION - SYMPHATHETIC Parasympathetic Response The parasympathetic does the opposite, it constricts the pupils. Parasympathetic nervous system contracts the ciliary muscle and provides near vision. Decreased heart rate and contractility Constriction of the bronchiole In terms of the GI tract, it causes the smooth muscle walls of the **The Preganglionic Neuron in RED, Postganglionic Neuron in BLUE digestive tract to contract and it causes the sphincters to relax Increased saliva secretion **Two Main Neurotransmitters Increased gastric acid secretion Acetylcholine Increased pancreatic secretions Noradrenaline (Norepinephrine) In terms of the bladder, you get detrusor muscle contraction and you get relaxation of the sphincter - So, all preganglionic neurons in both the parasympathetic and Role in Male genitalia: erection POINT/ERECTION-PARASYMPATHETIC sympathetic nervous system release acetylcholine as their neurotransmitter. - Almost all postganglionic sympathetic neurons except those which II. SYMPATHETIC DIVISION innervate sweat glands are noradrenergic. - They secrete noradrenaline to their target organ so the ones that do innervate sweat glands are acetylcholine secreting. More complex than parasympathetic - The postganglionic neuron secretes acetylcholine in the Innervates more organs parasympathetic nervous system. ○ Supplies not only all visceral organs in the internal cavities; - The adrenal medulla is actually directly innervated by the it also supplies visceral structures in the superficial region preganglionic neurons of the sympathetic nervous system of the body such as - The adrenal medulla then releases adrenaline and noradrenaline Sweat glands directly into the circulation Hair raising arrector pili muscles of the skin (Scared) Smooth muscles in the walls of arteries and vein It has more ganglia compared to parasympathetic ○ Sympathetic trunk ganglia (lateral to the vertebral column) ○ Collateral Ganglia (anterior to the vertebral column) **General Functions Sympathetic – Fight or Flight Parasympathetic – Rest and Digest **Application - A caveman who's running away from the lion so in response to: Sympathetic Response You get pupil dilation, it allows more light into the eyes that can increase your visual acuity, and so you can see a nice escape route and run away from that lion. Sympathetic nervous system dilates the ciliary muscle allowing far vision. Need to increase your heart rate and increase your heart's contractility to increase your cardiac output to get away from the lion Figure 8. Sympathetic Division of Autonomic Nervous System Dilates the bronchioles to allow more oxygen into the body. The blood vessel supplying the skin constrict and blood is shunted A. SYMPATHETIC DIVISION towards skeletal muscle so this would allow the caveman to run away from that lion. “FIGHT OR FLIGHT” The sweat glands in the skin are stimulated. Increased sweating so it's Larger of the 2 parts – more diverse than parasympathetic preparing for that increase in heat when you're about to run away or Widely distributed throughout the body fight and you also get contraction of the pili motor muscles. Innervates the heart and lungs, muscle if the blood vessels, hair You'll need those energy substrates in your body to be mobilized so follicles and the sweat glands, abdominopelvic viscera the glycogen stores in your liver are mobilized and you get glycogen “PREPARE the body for emergency” breakdown and an increase in blood sugar. (Glycogenolysis, ○ Increased heart rate – to deliver more oxygen and Page 4 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO blood to the skeletal muscle ○ Pupillary dilation – let more light for clearer vision ○ Bronchodilation – let more air to the lungs and increase oxygen uptake ○ Liver releases more sugar into the blood to provide energy ○ Arterioles of the skin and intestines are constricted - leads to cold skin, diversion of blood to more vital organ ○ Arterioles of the skeletal muscle are dilated, more blood goes to the skeletal muscle ○ Blood pressure is raised ○ The hair is made to stand on end, and sweating occurs. **In a fight or flight situation, non-essential functions such as digestion Figure 10. Sympathetic Chain Ganglia and urinary tract are inhibited temporarily **Originates from the ventral horn cell and enters the ventral root then to the SYMPATHETIC DIVISION IS CONSISTS OF spinal nerve. It then gives rise to the white ramus communicantes which 1. PREGANGLIONIC NEURONS communicates with the ganglion. Now, the preganglionic fibers communicate Thoraco-Lumbar Division with sympathetic ganglia and will give rise to postganglionic neurons which will between T1 and L2 enter the gray ramus communicantes. This will now enter the spinal nerve to Cell bodies are in the lateral gray horns innervate the visceral effectors. Axons enter the ventral roots 2. GANGLIONIC NEURONS (GANGLIA) SYMPATHETIC CHAIN GANGLIA (Paravertebral ganglia) ANATOMY OF THE SYMPATHETIC GANGLIA - Lateral to the vertebral column - Control effectors in the body wall, head, neck, Each spinal cord consists of: limbs, and thoracic cavity Preganglionic fibers COLLATERAL GANGLIA (Prevertebral ganglia) Postganglionic fibers - Anterior to the vertebral column - Neurons innervates effectors in the Sympathetic Ganglia abdominopelvic cavity 1. Cervical sympathetic chain ganglia 3. SPECIALIZED NEURONS (Direct innervations of the Adrenal Gland) 2. Thoracic sympathetic chain ganglia - neurons in the interior of the suprarenal gland 3. Lumbar sympathetic chain ganglia - Modified sympathetic ganglion in the suprarenal 4. Sacral sympathetic chain ganglia gland (Adrenal Gland) 5. Coccygeal sympathetic chain ganglia - Neurons release neurotransmitters (Epinephrine **Grouped together in a sympathetic chain and Norepinephrine) that act like hormones B. SYMPATHETIC CHAIN GANGLIA (PARAVERTEBRAL GANGLIA) Control effectors in the body wall, head, neck, limbs, and thoracic cavity Figure 9. Locations of Ganglia. Page 5 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO cavity sympathetic trunk ganglia in at least three ways: - They are not paired and not segmentally arranged - They occur only in the abdomen and pelvis - They all lie anterior to the vertebral column (hence the name pre- vertebral)  The main collateral ganglia - The Celiac - Superior mesenteric - Inferior mesenteric - Inferior hypogastric ganglia Figure 11. Autonomic Nerves, Plexuses and Ganglia Figure 13. Collateral Ganglia. **Originates from the preganglionic fiber and enters the white ramus communicantes but does not synapse with the sympathetic chain ganglia. Rather, it exits the spinal nerve and synapses with the collateral ganglion. It then innervates visceral organs in the abdominopelvic cavity. FUNCTION OF COLLATERAL CHAIN GANGLIA Reduction of flow of blood to the visceral organs Decrease in activity of the digestive organs Stimulation of the release of glucose from glycogen in the liver Stimulates adipose cells to release energy reserves Relaxation of smooth muscle in the urinary bladder Causes ejaculation in males Figure 12. Anatomical Distribution of Sympathetic Postganglionic Fibers **Take note of the nerves involved and their ganglion and the organ they innervate FUNCTIONS OF SYMPATHETIC CHAIN GANGLIA Reduction of circulation to the skin - constriction More circulation to skeletal muscles Stimulates more energy production by skeletal muscles Releases stored adipose Stimulation of arrector pili muscles Dilation of pupils - accommodate more light Increase heart rate Dilation of respiratory tubes - increase oxygen uptake D. SPECIALIZED NEURON C. COLLATERAL GANGLIA (PREVERTEBRAL GANGLIA) Modified sympathetic ganglion in the suprarenal gland (Adrenal Gland) Neurons innervate effectors in the abdominopelvic Page 6 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO -Responsible for direct innervation of the adrenal gland postganglionic neuron through the gray ramus communicantes that enter again Neurons release neurotransmitters (Epinephrine and to the spinal nerve, afterwards it finally goes to the effector organs. Norepinephrine) that act like hormones 2. SYNAPSE IN THE TRUNK GANGLION AT A HIGHER OR LOWER LEVEL SUPRARENAL MEDULLAE The preganglionic axon ascends or descends in the sympathetic trunk Fibers pass through sympathetic chain and the celiac ganglion to synapse in another trunk ganglion. The postganglionic fiber exits without synapsing the sympathetic trunk via the gray ramus communicans at the level of Proceed to the suprarenal medulla the synapse. Fibers then synapse on modified neurons that when stimulated will release neurotransmitters that act as hormones: **From the lateral horn, it goes to the ventral root, to the spinal nerve, white - Epinephrine and norepinephrine ramus communicantes, then it either goes up or down to communicate with another ganglion. It then goes out to the spinal nerves, finally going to the effector organs. Figure 14. Suprarenal Medullae. **Comes from the ventral horn of the spinal cord, then it enters into the white ramus communicantes, but it by-passes the sympathetic chain Figure 16. Synapse in trunk ganglion at a higher or lower level ganglia, without synapse. It enters directly the suprarenal medullae, and the synapse is only within this area, in order to stimulate the release of the 3. PASS THROUGH SYMPATHETIC TRUNK IN A COLLATERAL GANGLION epinephrine and norepinephrine into the general circulation. ANTERIOR TO THE VERTEBRAL COLUMN - The preganglionic axon passes through the sympathetic trunk, exits FUNCTIONS OF THE SUPRARENAL MEDULLAE on a splanchnic nerve, and synapses in a collateral ganglion. Increase alertness (epinephrine and norepinephrine) by activating the - The postsynaptic fiber extends from the collateral (known as the reticular activating system celiac ganglion) ganglion to the visceral organ via an autonomic nerve Increase cardiovascular and respiratory activity plexus. Increase muscle tone Increase the mobilization of energy reserves Increase release of lipids from adipose cells Increase breakdown of glycogen in liver cells MAJOR EFFECT PRODUCED BY PREGANGLIONIC FIBERS INNERVATING THE SUPRARENAL MEDULLAE: Release of epinephrine and norepinephrine into the general circulation. E. THREE PATHWAYS OF THE SYMPATHETIC GANGLIA Figure 17. Pass through sympathetic trunk in a collateral ganglion anterior to the vertebral column F. ADRENAL MEDULLA OF THE ADRENAL GLAND Figure 15. Synapse in trunk ganglion at the same level 1. SYNAPSE IN TRUNK GANGLION AT THE SAME LEVEL The internal portion of this gland- the adrenal medulla- is a **From the lateral horn to the ventral horn, then to the ventral root. It then goes major organ of the sympathetic nervous system. to the spinal nerve, the ventral ramus, to the white ramus communicantes, which These neuron-derived cells secrete great quantities of two synapses with the sympathetic ganglion, then from there it releases the excitatory hormones into the blood of nearby capillaries during the fight-or-flight response Page 7 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO Hormones secreted are norepinephrine (the chemical secreted ○ dorsal root carries sensory information as the ventral horn carries by other postganglionic sympathetic neurons as a motor information neurotransmitter) and greater amounts of a related excitatory ○ bulge seen is the dorsal root ganglion with the dorsal and ventral rami molecule called epinephrine (adrenaline) at the ends of the dorsal root ganglion A “surge of adrenaline” (ex: lifting heavy objects that you normally could not lift) Figure 19. Parts of the lateral horn ○ white and gray rami communicans are seen connecting to the sympathetic ganglion which are parts of the sympathetic trunk white ramus communicans - white because these are myelinated; some of the preganglionic neurons form a synapse with the postganglionic neurons within the sympathetic ganglion and leave through the gray ramus gray ramus communicans - gray because this is unmyelinated; the postganglionic neurons leaving the gray ramus the joins back to the spinal nerve and follows to the target organ for supply Figure 18. Sympathetic innervation of the adrenal medulla G. SUMMARY OF SYMPATHETIC DIVISION Consists of parallel chain on either side of the spinal cord Preganglionic fibers are short and extend from the spinal cord to the sympathetic chain Postganglionic fibers are long and extend from the spinal cord to the body organs The sympathetic division shows considerable divergence (3 pathways) All preganglionic neurons release ach/ most post ganglionic neurons release norepinephrine (some also release ACh) H. SYMPATHETIC NERVOUS SYSTEM - BASIC CONFIGURATION (From Supplementary Video) Figure 20. The Gray and White Ramus Communicans RECAP: SUMMARY OF FLOW: preganglionic nerve enters the ganglion, synapses and Sympathetic nervous system has 2 divisions leaves through the gray ramus to join the spinal nerves ○ Sympathetic division - fight or flight response; main role is to respond to different stresses of the body The regions above and below T1 - L2 where the preganglionic neurons can ○ Parasympathetic division - rest and digest response ascend or descend Autonomic nervous system has two (2) neuron system connecting the 1. sympathetic fibers that supplies the head and neck ascend to the Central and Peripheral Nervous System which involves cervical ganglia ○ preganglionic neuron ○ postganglionic neuron ANATOMICAL ASPECTS OF SYMPATHETIC NERVOUS SYSTEM EFFERENT OUTFLOW ○ originates in the lateral horn of the spinal cord from T1 - L2 segments ○ preganglionic neuron exits the spinal cord via the ventral horn ○ on either side of the vertical column, sympathetic trunk is seen - sympathetic trunk - chain of ganglia which extends from the base of the skull to the coccyx - sympathetic ganglia referred to as the power vertical ganglia (they lie on either side of the vertical column) Page 8 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO I. SYMPATHETIC NERVOUS SYSTEM - DISTRIBUTION (From Supplementary Video) The branches of the sympathetic chain has somatic and visceral distribution 1. Somatic- relates to the skin and the body wall 2. Visceral- relates to internal organs Each spinal nerve has a contribution from at least one gray ramus and this supplies the segmental skin area with these sympathetic fibers Figure 21. Sympathetic Supply of theHead and Neck Somatic- Relates to the skin and body wall Visceral- Relates to the internal organs. Somatic - Each spinal nerve has a contribution from at least one gray ramus 2. some sympathetic fibers that have own nerves that do not join the and this supplies a segmental skin area with these sympathetic spinal nerves (autonomic fibers that travel within their own nerve) are fibers called SPLANCHNIC NERVES - Sympathetic nerve fiber leaves ventral horn and enters the - some preganglionic fibers which synapses in the sympathetic ganglion via white ramus and then forms a synapse with sympathetic ganglion and the postganglionic neuron the post ganglionic neuron which leaves via gray ramus and travels in leaves to its own nerve the spinal nerve to supply the skin. Figure 24. Illustration of Somatic distribution Figure 22. Illustration of preganglionic fibers synapsing the sympathetic region and postganglionic neuron leaving to its own nerve This kind of sympathetic innervation provides three functions, it provides, vasomotor, pilomotor and sudomotor function to the skin - Some preganglionic fibers bypass the sympathetic - Vasomotor- Vasoconstricts arterials in the skin ganglion completely and do not form any synapse in the - Pilomotor- Supplies the arrector pili muscles sympathetic ganglion. It will synapse in peripheral ganglia - Sudomotor- Supplies sweat glands near the target organ Figure 23. Illustration of synapsing on the peripheral nerve delivering to the Figure 25. Featuring vasomotor, pilomotor and sudomotor function to the target organ skin Page 9 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO You get this kind of configuration in which the skin is supplied by sympathetic fibers at very spinal level Figure 27. Illustration of splanchnic nerves and its types Figure 26. Illustration of skin is supplied by sympathetic fibers at very spinal level Abdominopelvic splanchnic nerves Visceral - This project the ganglia which are located in front of the - A case of a sympathetic innervation to the head and neck vertebrae, around the various branches of the aorta. - To lower abdominal and pelvic visceral through sacral - Celiac ganglia splanchnic nerve - Superior mesenteric ganglia - Head and neck sympathetic fibers arise from the ganglia in the - inferior mesenteric ganglia sympathetic chain. And these fibers supply the skin in the eyes - aorticorenal ganglia - superior hypogastric ganglia The neurons ascend into the cervical ganglia and then the post - inferior hypogastric ganglia ganglionic fibers ascend along blood vessels that go to the head - and you also hear too as plexuses and neck. Blood vessels which supply the head and neck structures so the Splanchnic nerves vertebral arteries and the internal carotid arteries. - Thoracic splanchnics - Lumbar splanchnics - Sacral splanchnics - Pelvic splanchnics- (Part of parasympathetic) Figure 26. Illustration of sympathetic innervation to the head and neck Thoracic Viscera - This supplied by sympathetic outflow from spinal regions Figure 28. Illustration of Abdominopelvic splanchnic nerves T1 -T4 - The organs in the thorax are supplied by various plexuses. Thoracic Splanchnic - The pre ganglionic neuron for the thoracic organs enter - Greater Thoracic Splanchnic nerve- arises from T5-T9 the sympathetic ganglion, and instead of leaving by the and it synapses it the celiac gray ramus and along the spinal nerve like the somatic - Lesser Thoracic Splanchnic nerve- Arises from T10-T11 supply, they leave by their own nerve. and synapses with superior mesenteric and aorticorenal - Remember that autonomic nerve that take off on their ganglia own without traveling in the spinal nerve are known as - Least Splanchnic nerve- Arises from T12 and synapse splanchnic nerve with aorticorenal ganglia Splanchnic Nerve Lumbar Splanchnic - Supplies the heart and the lungs known as - Projects to the inferior mesenteric ganglia Cardiopulmonary splanchnic nerves - Important to know that these splanchnic nerves are post Sacral Splanchnic synaptic - Project to the inferior hypogastric plexus - These cardiopulmonary postsynaptic sympathetic fibers project by these splanchnic nerves to various plexuses then distribute to target organ Page 10 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO Cranial Outflow: (originates from the brain stem and innervates the head, neck, thorax and most of the abdomen) ○ Cranial Nerves III- Oculomotor (Edinger Westphal nucleus) VII- Facial (Superior salivatory nucleus & lacrimal nucleus) IX- Glossopharyngeal (Inferior salivatory nucleus) X- Vagus (Dorsal nucleus of vagus) Sacral Outflow: (supplies the distal portion of the digestive or pelvic organs) ○ Sacral Spinal Cord S2, S3, S4 ○ Innervation on distal part of large intestine, urinary bladder, reproductive organs, erectile tissues of external genitalia Figure 29. Featuring the thoracic, lumbar and sacral splanchnic nerves Adrenal glands - The adrenal medulla of the adrenal gland is special because the pre ganglionic fiber is directly innervated. - The adrenal medulla itself is like a ganglion, so the pre ganglionic fibers pass directly through the celiac ganglion without forming any synapse and then these fibers make direct contact with the medullary cells. - Neurotransmitter: Acetylcholine - When activated, this stimulates the adrenal medulla to release adrenaline and noradrenaline directly into the circulation. Figure 31. Parasympathetic Division of ANS **The postganglionic cell bodies of these cranial nerves lie on the ganglionic neurons, which are within the visceral organs. Figure 30. Featuring Adrenal glands and its innervation III. PARASYMPATHETIC DIVISION Most active when the body is at rest Concerned with conserving energy Direct vital “housekeeping” activities (digestion, elimination of feces and urine) “REST AND DIGEST” Preganglionic neurons are in the brainstem and sacral segments Preganglionic neurons do not diverge as much as the sympathetic division (Therefore, the sympathetic division is more localized and specific as compared to the sympathetic division) Postganglionic neurons are near (terminal) the target organ or within Figure 32. Autonomic Distribution of the Parasympathetic Output (intramural) the target organ **Sacral outflow emerges from the S2-S4 portions of the spinal cord, continuing where the vagus ends. A. PARASYMPATHETIC OUTFLOW Page 11 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO B. ORGANIZATION AND ANATOMY OF THE PARASYMPATHETIC DIVISION Preganglionic fibers leave the brain via: 1. CN III (to the intrinsic eye muscles, pupil, and lens 2. CN VII (o the tear (Lacrimal) glands and salivary glands (Submandibular/ Sublingual) 3. CN IX (to the parotid salivary glands) 4. CN X (to the visceral organs of the thoracic cavity and abdominal cavity) Preganglionic fibers leave the sacral region via: Pelvic nerves (to the visceral organs in the inferior portion of the abdominopelvic cavity C. FUNCTIONS OF THE PARASYMPATHETIC DIVISION Pupil Constriction Secretion of digestive enzymes from digestive glands Increased smooth muscle activity of the digestive system Stimulation and coordination of defecation Contraction of the urinary bladder Constriction of respiratory passages Reduced heart rate Sexual arousal D. PARASYMPATHETIC ACTIVATION AND NEUROTRANSMITTER RELEASE All preganglionic and postganglionic fibers release ACh at their synapses and neuroeffector junctions Most stimulations are short lived due to the immediate breakdown of ACh Has cranial and sacral components by acetylcholinesterase (within 2-3 msec, ACh is hydrolysed into acetic acid Preganglionic fibers in the parasympathetic nervous system are longer and choline by the enzyme (AChE, which is located on the surface of the than the preganglionic fibers of the sympathetic nervous system, nerve and receptor membrane. The choline is reabsorbed into the nerve because the ganglia lies near or within the target organs ending and used again for synthesis of ACh). E. SUMMARY OF THE PARASYMPATHETIC DIVISION Involves CN III, CN VII, CN IX and CN X Involves sacral segments S2 to S4 All parasympathetic neurons are cholinergic Release of ACh stimulates nicotinic receptors on ganglionic neurons Release of ACh on neuroeffector junctions stimulates muscarinic receptors F. SUPPLEMENTARY VIDEO: Parasympathetic Nervous System Cranial outflow of the parasympathetic component is found within cranial nerves III (oculomotor), VII (facial), IX (glossopharyngeal) and X (Vagus) Vagus nerve has a wide distribution to several thoracic and abdominal viscera, thus it makes up the largest component of the parasympathetic division. Page 12 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO Vagus Nerve Functions of the Cranial Components: - Originates in the dorsal motor nucleus 1. Eyes- pupil constriction; lens accommodation - Located in the medulla 2. Glands- innervation of salivary and lacrimal glands - Wide distribution to the thoracic and abdominal viscera, thus it is 3. Heart- decreased rate and contractility distributed in various plexuses: 4. Lungs- bronchoconstriction; secretomotor function to the mucous ○ Cardiac Plexus glands in the gut ○ Pulmonary Plexus 5. Gut- increased peristalsis; relaxes sphincter ○ Myenteric Plexus: Meissner’s; Auerbach’s - Postganglionic fibers of the vagus nerve are very short Oculomotor Nerve - Origin in the midbrain at the Edinger Westphal nucleus - Extends to the ciliary ganglion - Innervated the ciliary muscle; lens accommodation; constriction of the pupil Sacral Component - Arises from spinal segments S2 to S4 - Give rise to the pelvic splanchnic nerves - Innervates the muscles of the rectum and inhibits the internal anal sphincter - Stimulates the detrusor muscle of the bladder wall and inhibits the internal urethral sphincter - When activated, it causes erection in males whereas the sympathetic Facial Nerve nervous system is responsible for ejaculation Superior salivatory nuclei is located in the pons and gives rise to the facial nerve Two branches of the facial nerve: ○ Greater petrosal nerve- synapses in the pterygopalatine ganglia, secretomotor function: lacrimal nasal, palatine ○ Chorda tympani- extends to the submandibular ganglion, this ganglion then provides secretomotor function to the submandibular and to the sublingual glands Glossopharyngeal Nerve - Inferior salivatory nucleus is located in the upper medulla and which gives rise to the glossopharyngeal nerve - Lesser petrosal branch of the Glossopharyngeal nerve extends to synapse in the otic ganglion - Otic ganglion provides postganglionic projections to the parotid gland IV. ANATOMICAL AND PHYSIOLOGICAL DIFFERENCES BETWEEN THE PARASYMPATHETIC AND SYMPATHETIC DIVISIONS Page 13 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO Page 14 of 15 [NEURO 1A] - LC18 - AUTONOMIC NERVOUS SYSTEM - DR. CRISPIN ALLAN VIADO **Various Neurotransmitters on Different Parts of Autonomic and Somatic Nervous Systems **Autonomic Distribution of Parasympathetic NS Page 15 of 15