Anatomy Lecture 4 (ANS, SNS) PDF

Lecture 4 The autonomic nervous system: Sympathetic efferent nerve fibers (sympathetic outflow); sympathetic afferent nerve fibers; sympathetic trunks and ganglia.  Autonomic Nervous System (ANS) Autonomic – Greek - autos (”self”) + nomos (“custom, law”); independent, living by one’s own...

Lecture 4 The autonomic nervous system: Sympathetic efferent nerve fibers (sympathetic outflow); sympathetic afferent nerve fibers; sympathetic trunks and ganglia.  Autonomic Nervous System (ANS) Autonomic – Greek - autos (”self”) + nomos (“custom, law”); independent, living by one’s own laws. ANS/Visceral motor system regulates smooth muscle, cardiac muscle, glands (secretion), and adipose tissue. ANS manages a multitude of involuntary processes responsible for the body’s homeostasis - heart rate, blood pressure, body temperature, respiratory airflow, pupillary diameter, digestion, energy metabolism, defecation, urination, sexual functions, adjusts internal water, electrolyte, nutrient, and dissolved gas concentrations in body fluids. Primary target organs - viscera of the thoracic and abdominopelvic cavities and some structures of the body wall, including cutaneous blood vessels, sweat glands, and piloerector muscles.  Somatic NS vs. Autonomic NS SOMATIC NS AUTONOMIC ANS  Ganglia  Does not have ganglia  Effectors – smooth muscles, cardiac muscles, glands,  Effectors – skeletal muscles adipocytes  Two-neuron chain for reaching the effector; first neuron  One Neuron for reaching the synapses with the second neuron in ganglion effector; cell bodies are in the CNS, axons extend in cranial/spinal nerves till skeletal muscles  Efferent pathways and ganglia - first neuron – lightly myelinated, second neuron – non-myelinated  Efferent pathways – thick heavily myelinated fibers  Neurotransmitters – preganglionic fibers release Acetylcholine, most postganglionic fibers –  Neurotransmitter - Acetylcholine norepinephrine (NE); the effect may be excitatory or (Ach) inhibitory  Activation of the Sympathetic Division (1) Heightens mental alertness (2) Increases metabolic rate (3) Decreases digestive and urinary functions (4) Activates energy reserves (5) Increases respiratory rate and dilates respiratory passageways (6) Increases heart rate and blood pressure (7) Activates sweat glands  Structure of Spinal Cord Spinal cord pair nerves: Cervical – 8 (C1 – C8) Thoracic - 12 (T1 – T12) Lumbar – 5 (L1 – L5) Sacral – 5 (S1 – S5) Coccygeal – 1 (Co1) Sympathetic Division Paravertebral ganglia – on the left and right side of the vertebral column linked together in a chain; form the left and right sympathetic trunks/chains. Prevertebral (collateral, preaortic) ganglia – anterior to vertebral column, form several plexuses around the major branches of the abdominal aorta. All preganglionic fibers of the sympathetic division arise from cell bodies of preganglionic neurons in spinal cord segments T1 – L2. Sympathetic part leaves thoracolumbar regions of the spinal cord with the somatic components of spinal nerves. Sympathetic trunks extend from neck to pelvis, but sympathetic fibers arise only from the thoracic and lumbar cord segments. Ganglia vary in size, position and number. Each sympathetic trunk has 23 ganglia: 3 cervical 11 thoracic 4 lumbar 4 sacral Superficial Structures Innervated by SNS  Sweat glands The hair-raising arrector pili muscles of the skin  Smooth muscle in the walls of all arteries and veins, both deep and superficial Paravertebral Sympathetic Trunk Paravertebral sympathetic trunk – the ascending and descending fibers. White rami communicants only occur in association with spinal nerves T1 to L2 Gray rami communicants are associated with all spinal ganglion. Fibers from spinal cord levels T1 to T5 pass predominantly superiorly. Fibers from T5 to L2 - pass inferiorly.  Ganglion Impar Ganglion impar/azygos/ganglion of Walter is a convergence of two pelvic sympathetic trunks at the end of the front of the coccyx.  SNS Adjustments  Vigorous physical activity:  Constricts visceral (sometimes cutaneous) blood vessels, shunting blood to active skeletal muscles and heart. Dilates the bronchioles in the lungs, increasing air flow (increasing oxygen delivery to body cells). Stimulates the liver to release more glucose into the blood to accommodate the increased energy needs of body cells. Reduces gastrointestinal tract motility  Directions of Postganglionic Neurons  Synapse at the same level - the synapse is in the same trunk ganglion.  Synapse at a higher or lower level - the preganglionic axon ascends or descends the sympathetic trunk to another trunk ganglion.  Synapse in a distant collateral ganglion - the preganglionic axon passes through the trunk ganglion and emerges from the sympathetic trunk without synapsing.  These preganglionic fibers help form several splanchnic nerves and synapse in collateral, or prevertebral ganglia (anterior to the vertebral column).  Unlike sympathetic trunk ganglia, the collateral gangia are neither paired nor segmentally arranged. They occur only in the abdomen and pelvis. Impulse Transmission Rami communicants – white and gray White rami - myelinated neurons Gray rami - not myelinated neurons White rami - only in the T1 – L2 cord segments. Gray rami carry postganglionic fibers from every trunk ganglion (cervical - sacral region). Rami communicants are associated only with the sympathetic division. Impulse Transmission at the Same Level Lateral horn (T1 - L2) preganglionic axon - ventral horn - white ramus communicant – ganglion & synapse - gray ramus communicant - the spinal nerve Three different types of tissue: Smooth muscle tissue – pilomotor fibers - arrector pili Blood vessels – vasomotor fibers (vasoconstriction) – blood vessels Glands – sudor-motor fibers (don’t release norepinephrine, release acetylcholine) – sweat glands. Impulse Transmission at the Higher or Lower Level Lateral horn (T1 - L2) preganglionic axon - ventral horn - white ramus communicant – ganglion – down/upward to the next ganglion – synapse – gray ramus communicant - the spinal nerve Three different types of tissue: Smooth muscle tissue – pilomotor fibers - arrector pili Blood vessels – vasomotor fibers (vasoconstriction) – blood vessels Glands – sudor-motor fibers (don’t release norepinephrine, release acetylcholine) – sweat glands. Synapse in a Collateral Ganglion Lateral horn (T1- L2) preganglionic axon - ventral horn - white ramus communicant – ganglion without synapsing - alternate tunnel – ganglion located in front of the vertebral column (preaortic/prevertebral/collateral/s ub-diaphragmatic ganglia) - synapsing - splanchnic nerve Cervical Part of Sympathetic Trunk Cervical part – only gray rami communicans (there are not white rami communicants) There are three cervical sympathetic ganglia: Superior cervical ganglion Middle cervical ganglion Inferior/thoracic cervical ganglion (stellate ganglion) Superior Cervical Ganglion  Location: C1-C2 level ant. to the longus colli and longus capitis mm., post. to the common and internal carotid aa.  Formation: C1-C4 spinal nerves (only gray rami)  Internal carotid plexus – ciliary ganglion  Internal carotid plexus - deep petrosal nerve – pterygopalatine ganglion Lacrimal gland - constricts the blood vessels and directly works on the gland, decrees lacrimation Glands in the oral, nasal cavities, sinuses  External carotid plexus Sup. Cervical Ganglion Innervation:  Heart – superior cervical cardiac nerve Eye – dilator pupillae; ciliary muscle (flattens the lens)  Salivary glands (↓blood supply & production of saliva; ↑protein secretion)  Lacrimal glands (↓blood supply and lacrimation)  Skin and blood vessels of the head  Inhibit the nasal glands Middle Cervical Ganglion  Location: C6 level  Formation: C5-C6 spinal nerves (gray rami communicants) Form a plexuses around inferior thyroid artery  Innervation: Larynx, trachea, pharynx, upper esophagus. Thyroid & Parathyroid glands (vasomotor effect, not secretomotor) Middle cervical cardiac nerve Inferior Cervical Ganglion Inferior/Cervicothoracic ganglion (the stellate ganglion) – via gray rami - plexuses around subclavian and vertebral arteries Location: C7 level Formation: C7, C8, T1 spinal nerves (gray rami) Innervation: Smooth muscles in the arteries Middle & Inferior Cervical Ganglion  Cardiac plexus – positive chronotropic action (↑ HR, cardiac output, BP)  Esophageal plexus – ↓ peristalsis  Pulmonary plexus – dealation, ↓ secretion, vasoconstriction of bronchial arteries Thoracic Ganglia  Thoracic spinal nerves  Intercostal nerves (ventral rami)  Thoracic Viscera  Thoracic cardiac nerves (T2 - T5) – join the cardiac plexus – affect myocardial system (↑contractility, cardiac output, BP – positive inotropic effect) & conduction system (↑heart rate – positive chronotropic effect) Esophagus – esophageal plexus – ↓peristalsis Bronchi – pulmonary plexus – bronchodilation, vasoconstriction (↓secretion of glands) Prevertebral Ganglia Prevertebral ganglia (splanchnic ganglia) - around the origin of the major branches of the abdominal aorta. The prevertebral ganglia form aggregations around the abdominal prevertebral plexus: Celiac ganglia – stomach, liver, pancreas, duodenum, initial part of small intestine Aorto-renal ganglia – small intestine Superior and inferior mesenteric ganglia – descending colon, sigmoid colon, rectum, urinary bladder, sexual organs  Greater Sympathetic preganglionic fibers from T5 to L1 Splanchnic innervate the abdomen. Preganglionic fibers (T5 - T9) – greater Nerves splanchnic nerves – celiac ganglion.  Stomach  Stomach & upper part of the duodenum - inhibits peristalsis  Decrease the blood supply  Decrease the absorption, secretion  Contraction pyloric sphincter  Liver  Glycogenolysis  Decrease biliary flow Pancreas  Decrease insulin production  Increase glucagon production  Adrenal gland (intramural ganglia)  Norepinephrine & epinephrin Sympathetic Innervation of the Adrenal Gland Some sympathetic nerves without synapsing project directly onto the medullary cells The cells themselves play the role of the postganglionic neurons by releasing neurotransmitters - epinephrin (adrenalin) directly into the blood stem (intramural ganglia). Release:  Norepinephrine  Epinephrine Lesser Splanchnic Nerves Lesser splanchnic nerve (T10 - T11) - superior mesenteric ganglion (superior mesenteric artery)  Intestines (ascending colon, cecum, transverse colon proximal 2/3, small intestine, distal duodenum, jejunum, ileum) Inhibits the GI tract  ↓Secretion  ↓Absorption (constriction of blood vessels) ↓Peristalsis Least Splanchnic Nerve Lesser splanchnic nerve (T12) – aorticorenal – Aorticorenal ganglion ganglion  Kidney (vasoconstriction) - ↓urine production (RAAS system – a renin angiotensin aldosterone system – helps produce more renin from the kidneys to help increase the blood pressure)  Bladder  Uterus  Ureter (decrease the peristalsis) Lumbar splanchnic nerves-inferior mesenteric ganglion Lumbar splanchnic nerves (L1, L2, L3) – inferior mesenteric ganglion (inferior mesenteric artery)  Supply:  Transverse column (distal 1/3) Descending colon  Sigmoid colon  Upper rectum Function: ↓ Peristalsis Superior hypogastric ganglion L1, L2, L3, L4 spinal nerves – superior & inferior mesenteric arteries:  Superior hypogastric ganglion Internal urethral sphincter Detrusor muscle  Intermesenteric plexus Gonads – ejaculation/uterine contraction Sacral Splanchnic Nerves Sacral splanchnic nerves (S1-S2) – inferior hypogastric plexus Urinary bladder Prostate gland Uterus & vagina Rectum & anal canal  Intermesenteric plexus Hindgut and pelvic organs Testis/ovaries  Visceral Sensory Neurons  Visceral sensory neurons send information about chemical changes, stretch, temperature, and irritation of the viscera.  The brain interprets this information as hunger, fullness, pain, or nausea.  Like somatic sensory neurons, the cell bodies of visceral sensory neurons are located in dorsal root ganglia and in the sensory ganglia of cranial nerves.  The axons of visceral sensory neurons travel in the same nerves as the autonomic motor fibers (many visceral sensory neurons accompany the parasympathetic fibers of the vagus nerve). Visceral Reflexes Components: Receptor in viscera Visceral sensory neuron Integration center/neuron motor neuron (two-neuron chain) Visceral effector. Thank you