Autonomic nervous system

• • Autonomic nervous system pathway differ from somatic ones in number of neurons between organ And CNS. In somatic pathway there is just one neuron, while in autonomic there are 2 neurons which synapse in peripheral ganglia.
  • Preganglionic neurons(1order): takes origin in brainstem/spinal cord and synapse with peripheral ganglia.
  • Postganglionic neuron(2order): origin in autonomic ganglia and synapse with effector organ.
• Sympathetic ganglia is found close to sympathetic center and therefore SNS preganglionic fibers are short while postganglionic SNS fibers are long→takes longer route to reach effector organs
• Parasympathetic ganglia is found father from PNS center therefore PNS preganglionic fibers are longer while postganglionic fibers are short and found close to their target organs
• • All preganglionic fiber use acethylcholine as neurotransmitter
  • Post ganglionic PNS→ acethylcholine
  • Post ganglionic SNA→norepinephrine
• Describe general design of sympathetic nervous system

  • Preganglionic neuron (at thoracic + lumbar segnments: T1-L2
  • Sympathetic ganglia: paravertebral + prevertebral
  • Postganglionic neuron: cell body in sympathetic ganglia. Their fibers (postganglionic norepinephrine) synapse into effector organ
• • Sympathetic preganglionic neurons are located in intermediolateral cell column (lat horn) of thoracolumbar spinal cord: T1-L2 segments
  • Pathway: axons of preganglionic neurons leave spinal cord via anterior roots→ pass through spinal nerves and enter sympathetic chain via white rami communicantes. (Continues)

  
• Sympathetic ganglia


  Two types:

  1. Paraverterbal( sympathetic chain) ganglia: occurs on either side of vertebral column→ linked in a chain extend from base of skull to coccyx. They are connected btw each other forming left and right sympathetic chain.
  2. Prevertebral ganglia (collateral ganglia) located anterior to vertebral column in abdominal cavity. They form plexuses around major branches of abdominal aorta

  
• After entering sympathetic chain via white rami communicants preganglionic fibers can follow 3 routes:

  • Synapse with postganglionic neurons in sympathetic chain ganglia at same level in spinal cord
  • Ascend/descend few levels and synapse with postganglionic neurons in sympathetic chain ganglia at different levels in spinal cord
  • Pass through sympathetic chain ganglia without synapsing combine with fibers from other levels to form and exit as splanchniv nerves and procede towards prevertebral ganglia
• Some preganglionic fibers do nit synapse either in prevertebral or paravertebral ganglia.

  These directly innervate adrenal medullam stimulating release of epinephrine snd norepinephrine into bloodstream which results into widespread sympathetic response
• Sympathethic Splanchnic nerves

  • Sympathetic fibers which pass through trunk without synapsing
  • Combine with other fibers to form splanchnic nerves
  • There are 5: greater, lesser, least, lumbar and sacral splanchinic nerves. These are collectively called abdominopelvic splanchnic nerves. After synapsing in prevertebral ganglia, postganglionic fiber follow main branches of aorta and supply all organs except adrenal gland in abdominal and pelvic cavities
• Cardiopulmonary Splanchnic Nerves: These nerves arise from the upper thoracic ganglia (T1-T4) and innervate the heart and lungs Through formation of smaller plexi:

  • They do not follow the typical splanchnic nerve pattern of passing through the chain without synapsing. Instead, they synapse in the sympathetic chain ganglia at corresponding levels.
  • Innervation: Heart (increases heart rate and force of contraction) and lungs (bronchodilation)
• The sympathetic chain consists of a series of ganglia interconnected by nerve fibers. There are typically 22-23 pairs of ganglia in humans:

  • 3 cervical ganglia (superior, middle, and inferior)
  • 12 thoracic ganglia
  • 4 lumbar ganglia
  • 4-5 sacral ganglia
  • 1 coccygeal ganglion (often fused into a single structure called the ganglion impar)

  
• Superior cervical ganglia

  • Sympathetic fibers from T1-T3 pass through chain ganglia and extend sup to cervical ganglia.
  • Postganglionic fibers join spinal nerve and supply erector pili, blood vessels, sweat glands, branches to heart, lungs and esophagus.
  • Postganglionic fibers also form carotid plexus which is swirl around internal carotid and supply dilator pupillae (dilation), ciliary muscle (accommodatio) and salivary gands (increase mucous production); lacrimal glands (decrease lacrimation)

  
• Middle and inferior cervical ganglia

  • Sympathetic fibers pass through chain ganglia and extend superiorlu to synapse in middle + inf cervical ganglia.
  • Postganglionic fibers form plexus that innervate heart, lungs,esophagus
  • Cardiac plexus: increase HR+ Bp
  • Esophageal plexus: decrease peristalsis
  • Pulmonary plexus: bronchial dilation
• Prevertebral gangliaCeliac ganglia: postganglionic fibers innervate

  • Stomach: inhibits peristalsi, decrease absorption + secretion
  • Liver: stimulates glycogenolysis and gluconeogenesis
  • Gall bladder: inhibits biliary secretion
  • Pancreas: decrease insulin production; increase glucagon production
  • Spleen: splenic contraction
  • Duodenum: decrease peristalsis
• Superior mesenteric ganglia

  • Preganglionic fibers exist as greater splanchinic nerve and synapse into celiac + sup mesenteric ganglia
  • Postganglionic fibers decrease peristalsi, absorption and secretion of distal half of duodenum, jejunum, ileum,cecum, ascending and transverse colon
• Adrenal medulla

  • Preganglionic fibers leave as greater splanchinic nerve and synapse with chromaffin cells of adrenal medulla
  • Postganglionic fibers (chromaffin cells) release nore and epinephrine to circulation causing diffuse, systemic effect
• The greater splanchnic nerve synapses with the following: o Celiac Ganglia

  o Superior Mesenteric Ganglia

  o Adrenal Medulla
• Aorticorenal ganglia

  • Fibers from T10-11 leave as lesser splanchinic nerve
  • Postganglionic fibers innevate kidney and ureter decreasing urinary production, renin production to increase BP
• Renal plexus

  • Preganglionic fibers from T12 synapse into renal plexus
  • Postganglionic fiber enter kidney causing decrease urinary production
• Inferior mesenteric plexus

  • Preganglionic fibers from L1-2 exist as lumbar splanchinic nerve
  • Postganglionic fibers supply transverse colon, descending colon, sigmoid colon and upper rectum causing decrease peristalsis and defecation
• Inferior hypogastric plexus

  • Preganglionic fiber from T10-L2 leave as sacral splanchnic nerve and synapse with inferior hypogastric plexus
  • Postganglionic fibers innervates gonads
  • In males: cause ejaculation and seminal fluid production
  • In females: in non -pregnant women cause uterine contractions
• Superior hypogastric plexus


  Preganglionic fibers from T12-L3 synapse in superior hypogastric plexus

  Postganglionic fibers innervate internal urethral sphincter and detrusor to decrease micturition
• Sympathetic chain ganglia

  
• Prevertebral Ganglia: located ant tovertebral column, near major abdominal arteries. Major Prevertebral Ganglia:

  • Celiac Ganglion: near celiac artery; innervates stomach, liver, spleen, and kidneys.
  • Superior Mesenteric Ganglion: near SMA artery; innervates the small intestine and parts of the large intestine.
  • Inferior Mesenteric Ganglion: near inferior mesenteric artery; innervates the distal large intestine, rectum, bladder, and reproductive organs.
  • Aorticorenal Ganglia ( innervates kidneys and adrenal glands.), sup hypogastric ganglion(testicles, ovaries, ureter), inf hypogastric
• Sympathetic chain ganglia:

  • These ganglia are involved in the sympathetic innervation of the body. Preganglionic fibers from the spinal cord enter these ganglia via the white rami communicantes.

  They can either synapse with postganglionic neurons within the same ganglion or travel up or down the chain to synapse at different levels.

  Postganglionic fibers exit the ganglia via the gray rami communicantes to innervate target organs
• Prevertebral ganglia

  Preganglionic fibers from the spinal cord pass through the paravertebral ganglia without synapsing and continue as splanchnic nerves to these prevertebral ganglia.

  Here, they synapse with postganglionic neurons that innervate abdominal and pelvic organs.
• The SNS prepares the body to handle stressful situations by:

  • Increasing heart rate and blood pressure.
  • Dilating airways to improve oxygen intake.
  • Inhibiting digestive activities.
  • Mobilizing energy stores.
  • Dilating pupils to improve vision.
  • Stimulating sweating for thermoregulation.
  • Inhibiting urination to prevent distraction.
  • Releasing adrenaline and noradrenaline to sustain and amplify the sympathetic response.
  • Facilitating reproductive functions during sexual activity.
• (α1) Receptors:

  • Location: Blood vessels, GIT, bladder.
  • Function: Vasoconstriction, smooth muscle contraction.

  (α2) Receptors:

  • Location: Nerve terminals, CNS.
  • Function: Inhibition of neurotransmitter release, vasoconstriction

  (β1) Receptors:

  • Location: Heart, kidneys.
  • Function: Increased heart rate, force of contraction, conduction velocity in the heart, stimulate renin release from kidneys.

  (β2) Receptors:

  • Location: Lungs, skeletal muscle blood vessels, liver, gastrointestinal tract.
  • Function: Bronchodilation, vasodilation in skeletal muscle blood vessels, glycogenolysis, gluconeogenesis.
• • The parasympathetic nervous system originates in the brainstem and the sacral region of the spinal cord.
  • The cranial component involves oculomotor, facial, glossopharyngeal and vagus nerves
  • The sacral component arises from the sacral spinal cord segments (S2-S4).
• 2. Oculomotor n: origin (edinger-westphal nucleu) gives preganglionic fiber that synapse into ciliary gangli. Postganglionic fiber pierces sclera and ciliary m.→ Ciliary muscle constriction (accommodation) + pupils constriction.

  3. Facial n: origin in sup salivatory nucleus in pons→ preglanglionic axons synapse into: pretygopalatine ganglion (postganglionic fiber stimulate lacrimal, nasal and palatine glands)

  Submandibular glanglion: postglanglionic fiber supply submandibular + sublingual glands.

  
• 1. Course of cranial nerves in Parasympathetic Ns

  • Hypothalamus has parasympathetic cent er that gives presynaptic fibers that descend to stimulate nuclei of cranial nerves
• 4. Glossopharyngeal n: in inferior salivatory nucleus in lower pons. Preganglionic axons synapse in optic ganglion; Postganglionic fibers innervate parotid gland stimulating salivary secretion

  5. Vagus n: origin in dorsal nucleus of vagus in medulla. preganglionic fibers synapse into:

  • lung: pulmonary plexus: bronchoconstriction and increase secretion
  • heart:cardiac plexus: decrease firing AP on SA and Av node causing decrease in HR + BP
  • esophagus: esophageal plexus: increase peristalsis
  • intestine: celiac plexus: increase motility,secretions
  • Liver + gall bladder: hepatic plexus: glycogenesis

  
• course of parasympathetic sacral outflow

  • Origin in nuclei of S2,3,4
  • Course: from spinal cord→pelvic splanchinic nerves→inferior hypogastric plexus→ supply anything that vagus did not
  • Gonads, detrusor m of gallbladde, internal ana and urethral sphincter, descending colon, sigmoid colon, rectum, distal 1/3 of transverse colon

  Action:

  • increase motility in colon, stimulates rectum and internal anal sphincter, bladder contraction, male erection, clitoris engorgement
• Summary of Parasympathetic Functions and Anatomy

  • Heart: Decreases heart rate and force of contraction.
  • Lungs: Constricts bronchi, promoting a restful state.
  • Digestive System: Increases peristalsis and secretion of digestive enzymes, aiding digestion.
  • Eyes: Constricts pupils and adjusts lens for near vision.
  • Salivary and Lacrimal Glands: Stimulates secretion of saliva and tears.
  • Urinary Bladder: Promotes bladder contraction and urination.
  • Reproductive System: Enhances blood flow to the genital area, facilitating arousal.
• Parasympathetic outflow

  
• Parasympathetic Receptors

  1. Muscarinic Receptors (M1, M2, M3, M4, M5)

  • M1 : Found in CNS and gastric glands; involved in cognitive functions and gastric acid secretion.
  • M2: in the heart; reduce heart rate and force of contraction.
  • M3: : Found in smooth muscles and glands; stimulate smooth muscle contraction and glandular secretion.
  • M4 and M5: Present in the CNS; have roles in modulating neurotransmission.

  1. Nicotinic Receptors: at the neuromuscular junctions and autonomic ganglia; involved in muscle contraction and neurotransmission within the autonomic nervous system.
• Parasympathetic nervous system

  
• NOTE: don’t confuse the pelvic splanchnic nerves with the sacral splanchnic nerves (these are for the sympathetic system). The parasympathetic system has the pelvic splanchnic nerves.
• Sympathethic nervous system ganglia