pathophys2 final: Autonomic Nervous System ppt

Autonomic Nervous System (ANS)

• Maintains steady state among organs; regulator of cardiac muscle, smooth muscle, glands
• Targets:
  • Smooth muscles (blood vessel walls, alimentary canal, urinary bladder)
  • Glands (sweat glands, respiratory and GI tract)
  • Cardiac muscle and cardiac electrical conduction system
• Peripheral nerves gather information from target tissues through special sensory receptors:
  • Chemoreceptors (send signals about pH, oxygen partial pressure)
  • Mechanoreceptors (measure wall tension and pressure in blood vessels and viscera)
  • Nociceptors (relay signals interpreted as pain when viscera are damaged and/or overdistended)

Sensory Component (Afferent)

• Long processes go from specialized receptors in peripheral tissues to cell bodies in the dorsal root ganglia of the spinal cord
• Information is transmitted to the spinal cord by short axons for processing, integration with other signals, and autonomic reflexes

Motor Component (Efferent)

• Two-neuron system (preganglionic and postganglionic neurons)
• Preganglionic (myelinated) neurons synapse with postganglionic neurons in ganglia
• Postganglionic (unmyelinated) neurons transmit signals to target organs

Autonomic Nervous System Divisions

• Sympathetic (Fight or Flight)
  • Paravertebral ganglia (chains along the spinal column)
  • Prevertebral ganglia (around the aorta branches)
  • Neurotransmitters: epinephrine and norepinephrine
• Parasympathetic (Conservation/Restoration of Energy)
  • Ganglia located near or embedded in target organs
  • Neurotransmitters: acetylcholine

Sympathetic Nervous System

• Thoracolumbar (T1-L2)
• Longitudinal set of ganglia lying next to the spinal cord
• Short preganglionic neurons originate at the spine, synapse with post-ganglionic neurons, and head to effector organs

Parasympathetic Nervous System

• Craniosacral (cell bodies originate in cranial nerve nuclei and sacral spinal cord)
• Ganglia exist in the periphery, close to organs they innervate
• Most travel out to the periphery via the VAGUS and pelvic nerves
• Affects cardiac conduction

Anatomical Differences

• Sympathetic: ganglia close to the spinal cord, long postganglionic fibers, lots of branching
• Parasympathetic: ganglia close to target organs, short postganglionic fibers, little branching

Adrenal Medulla

• Endocrine gland that behaves like a sympathetic ganglion
• Sympathetic nerve fibers from the sympathetic trunk → Adrenal Medulla → Epi/Norepi released directly into the bloodstream

Autonomic Nervous System Neurotransmitters

• Sympathetic PREGanglionic fibers: acetylcholine (cholinergic receptor)
• Sympathetic POSTganglionic fibers: norepinephrine (adrenergic receptor)
• Parasympathetic PREGanglionic and POSTganglionic fibers: acetylcholine (cholinergic receptor)

Adrenergic Receptors

• G-protein coupled receptors
• α-adrenergic receptors:
  • α1 (excitation/stimulation, most common)
  • α2 (relaxation/inhibition)
• β-adrenergic receptors:
  • β1 (increase heart rate, contractility, and renin release)
  • β2 (relaxation of bronchi, bladder, and other muscles)
  • β3 (lipolysis and thermogenesis)

Clinical Correlation

• Vasopressors/Inotropes: Norepinephrine, Epinephrine, Dopamine, and inotropic drugs (Dobutamine, Milrinone)
• Smoking: Nicotine acts as a nicotinic receptor agonist, involved in reward pathways with dopamine
• Quitting smoking: Use a nicotinic receptor antagonist (Varenicline, Chantix)
• Muscarinic receptor antagonist (Atropine): blocks PSNS input to the iris (pupil dilation), cardiac conduction system (treats bradycardia), and GI smooth muscle

Comparing Receptors

• Nicotinic receptors:
  • Ion-gated channels
  • Found in muscles, CNS, autonomic, and more
• Muscarinic receptors:
  • G-protein coupled receptors
  • Found in glands, eyes, bladder/GI smooth muscle, and more

Learn about the Autonomic Nervous System, its functions, and target tissues including smooth muscles, glands, and cardiac muscles.