Summary
Highlights
The video introduces the sympathetic and parasympathetic nervous systems as part of an NCLEX review series on the neuro system and pharmacology. It outlines the content to be covered: anatomy, affected organs, signs and symptoms, and related medications. The nervous system is divided into the central (brain and spinal cord) and peripheral systems. The peripheral system includes somatic (voluntary) and autonomic (involuntary) divisions, with the autonomic further divided into sympathetic and parasympathetic branches. The peripheral nervous system consists of 12 cranial nerves and 31 spinal nerves (cervical, thoracic, lumbar, sacral, coccygeal).
This section details the sympathetic nervous system, known for the 'fight-or-flight' response, which prepares the body for stress and survival. Neurons predominantly originate from the thoracic and lumbar regions. Preganglionic neurons release acetylcholine (cholinergic fibers), while most postganglionic neurons release norepinephrine (adrenergic fibers), acting on alpha and beta receptors. Exceptions include sweat glands (releasing acetylcholine) and renal vessels (releasing dopamine). The adrenal medulla is directly stimulated by preganglionic neurons to release epinephrine and norepinephrine into the bloodstream, sustaining the 'fight-or-flight' response.
When stimulated, the sympathetic nervous system causes pupil dilation, decreased salivary production, increased heart rate (tachycardia), increased blood pressure, bronchodilation, and liver glycogenolysis (increased blood sugar). Intestinal motility decreases, and the bladder relaxes. Medications that mimic this system are called sympathomimetics or adrenergic agonists, such as dopamine, norepinephrine (Levophed), and epinephrine (EpiPen), used for shock or severe bronchoconstriction. Beta-2 adrenergic agonists like albuterol or salmeterol are used for respiratory issues. Side effects include high heart rate, hyperglycemia, nervousness, jitteriness, and dry mucous membranes.
The parasympathetic nervous system, or 'rest and digest' system, functions to restore the body after stress. Its preganglionic neurons are longer, and postganglionic neurons are shorter compared to the sympathetic system. Neurons mainly originate from the brainstem (affecting cranial nerves 3, 7, 9, and the vagus nerve (cranial nerve 10)) and the sacral area. All pre- and postganglionic neurons in this system are cholinergic, releasing acetylcholine. The vagus nerve is crucial for its widespread effects on the heart, lungs, and GI system. It helps the body recover from sympathetic overdrive.
Parasympathetic stimulation causes pupil constriction, increased salivary production, slowed heart rate, relaxed arteries leading to lower blood pressure, bronchoconstriction, increased gastric motility, and bladder constriction (aiding voiding). Drugs that stimulate this system are called parasympathomimetics or cholinergic drugs, like pyridostigmine, used in myasthenia gravis to improve muscle function. Side effects of cholinergic drugs include smaller pupils, increased saliva, increased mucus production (leading to coughing), increased intestinal motility, diarrhea, stomach pains, and cramping.
Drugs that inhibit the sympathetic system are sympatholytics or adrenergic antagonists, which block norepinephrine release, leading to parasympathetic-like effects. These are used for hypertension or anxiety, like beta-blockers (e.g., propranolol), which decrease heart rate. Side effects include bradycardia and potential bronchoconstriction (with non-selective beta-blockers). Drugs that inhibit the parasympathetic system are anticholinergics, blocking acetylcholine release, leading to sympathetic-like effects. Examples include ipratropium (a bronchodilator for asthma) and atropine (used to increase heart rate in bradycardia or dilate pupils).