This NCLEX review will discuss the sympathetic and parasympathetic nervous system along with pharmacology.
As a nursing student, you must be familiar with how these two nervous systems work and how medications inhibit or stimulate these systems.
These type of questions may be found on NCLEX and definitely on nursing lecture exams.
Don’t forget to take the sympathetic vs parasympathetic system quiz.
You will learn the following from this NCLEX review:
- Definition of each system
- Signs and Symptoms
Sympathetic and Parasympathetic Nervous System Lecture
Sympathetic vs. Parasympathetic Nervous System (Includes Pharmacology)
The sympathetic and parasympathetic nervous systems are part of the AUTONOMIC nervous system, which is a branch of the PERIPHERAL NERVOUS SYSTEM. The other branch of the peripheral nervous system is the somatic nervous system. The peripheral nervous system arises out of the central nervous system, which includes the brain and spinal cord.
What is the difference between the autonomic and somatic nervous system since they are both part of the peripheral nervous system? The autonomic system (sympathetic and parasympathetic) controls the involuntary functions of our internal organs and glands. For example, the sympathetic nervous system helps our body deal with stress and is known as the “fight or flight” system. While the parasympathetic balances out our system when the stressor is removed and allows our body to rest. This system is known as the “rest and digest” system.
In contrast, the somatic system controls the voluntary functions of our body. For example, if you touch something hot, your central nervous system processes this information and sends it to your peripheral nervous system, which causes your somatic system to immediately remove your hand from the hot item.
The autonomic system is unique because it has TWO neurons that synapse (come together) in an autonomic ganglion . This is important because each system (sympathetic and parasympathetic) each have preganglionic and postganglionic neurons, which are made up of special fibers (like cholinergic, adrenergic etc.) and this determines what type of neurotransmitters will be released.
Sympathetic Nervous System: Fight or Flight
Where are the sympathetic neurons located? In the thoracic and lumbar areas, which will supply certain organs by the postganglionic neurons. These areas include the eyes, heart, lungs, liver, intestine, stomach, salivary glands, kidneys (adrenal glands), and uterus.
Anatomy of the sympathetic neurons:
- Leaving the spinal cord are SHORT preganglionic neurons made up of cholinergic fibers that release the neurotransmitter acetylcholine. These neurons synapse in the sympathetic ganglia with the postganglionic neurons. The postganglionic neurons are made up of ADRENERGIC fibers that release the neurotransmitter norepinephrine, which will target the specific organ/tissue receptors (alpha and beta).
- Note: for this lecture we will concentrate on the sympathetic postganglionic neurons that release norepinephrine. However, it is important to know the sympathetic postganglionic neurons that supply the renal vessels are made up of dopaminergic fibers, which release the neurotransmitter dopamine. In addition, the sympathetic postganglionic neurons that supply the sweat glands are cholinergic fibers which release acetycholine.
How does the sympathetic system become stimulated? When your central nervous system perceives something stressful like getting robbed or being chased by a vicious animal, it causes the sympathetic system to kick into action. This system is going to try to keep you alive. Therefore, it doesn’t care about eating, excreting waste, reproducing….it needs to preserve your survival because that other stuff can happen later (hence where your parasympathetic system comes into play).
How does the body keep the sympathetic nervous system stimulated? By the stimulating the adrenal medulla in the adrenal glands. Going straight to the adrenal medulla is a preganglionic neuron made up of cholinergic fibers that will release the neurotransmitter acetylcholine, and this will cause the medulla to release NOREPINEPHRINE and EPINEPRHINE.
Signs and Symptoms produced by Sympathetic Nervous System:
- Elevated blood pressure
- Pupils dilate: cells of the radial muscle contract
- Dilatation of arterioles to skeletal muscle: this will help you run and get out of danger
- Increase blood sugar: glycogenolysis of glucose in liver
- Contraction of sphincters: no bowel movements
- Relaxation of the bladder (not urination) and uterus
- Stops salivation along with decreasing gastric motility
- Bronchodilation: breathe easier to run
- Causes kidney’s adrenal glands to release catecholamines: epinephrine and norepinephrine, which will majorly allow sympathetic response to continue
Parasympathetic: Rest and Digest
Where are the parasympathetic neurons located? In the brain stem and sacral area, which will stimulate the cranial nerves and other organs to produce opposite effects that the sympathetic nervous system caused.
Anatomy of the parasympathetic neurons:
- Leaving the spinal cord/brain stem are LONG preganglionic neurons made up of cholinergic fibers that release the neurotransmitter acetylcholine. These neurons synapse either in the cranial ganglion (neurons coming out of the brain stem), terminal ganglia where it meet the internal visceral organ, or at the pelvic ganglia with the postganglionic neurons. The postganglionic neurons are made up of CHOLINERGIC fibers that release the neurotransmitter acetylcholine, which will target the specific organ/tissue receptors.
How does the parasympathetic system become stimulated? When your central nervous system perceives the stressor is removed the parasympathetic system starts to take over and undo all the signs and symptoms the sympathetic system caused. This system is going to help you recover. Therefore, it cares about eating, excreting waste, reproducing….it needs to replenish the system of its depleted energy and glucose along with allowing the internal organs to rest.
Neurons leaving the brain stem do the following:
- cranial nerve III: constrict pupils
- cranial nerve VII and IX: stimulates salivary glands
- cranial X Vagus: this is a super important cranial nerve because it is responsible for producing MOST of the sign and symptoms we see with parasympathetic stimulation. The vagus nerve is a very long cranial nerve and it runs from the brain stem to major organs, such as the heart, lung, stomach etc. Therefore, it causes constriction of airway, lower heart rate/blood pressure, stimulation of digestion.
Neurons leaving the sacral area: relax sphincters, bladder to contract to void
Signs and Symptoms of the Parasympathetic System:
- Slower heart rate
- Decrease blood pressure
- Pupil constrict
- Increase gastric motility….bowel movements
- Contract bladder…..voiding
Medications that create or imitate the sympathetic nervous system:
- Sympathomimetic (imitate)…also called Adrenergic Agonists: these drugs are going to imitate the sympathetic nervous system response:
- Dopamine: increases blood pressure and output and renal perfusion by acting on alpha and beat receptors
- Norepinephrine (Levophed): increases blood pressure (vasoconstriction)
- Epinephrine: bronchodilation with an anaphylactic reaction…epi-pen
- Bronchodilators (like BETA 2 Adrenergic Agonists) inhaled: asthma, COPD “Albuterol, Salmeterol” ….causes bronchodilation
Side effects of these medications (same as the normal side effects of sympathetic stimulation): tachycardia, hyperglycemia, nervous, dry mucous membranes
Drugs that inhibit the sympathetic nervous system response:
Sympatholytic: (adrenergic antagonist): inhibit nervous transmission of nerve impulse in sympathetic nervous system and leads to a parasympathetic response.
- These are drugs used to treat hypertension (sometimes anxiety disorders): to help lower the blood pressure/heart rate
- Beta blockers (nonselective or selective): propranolol, sotalol
- Side effects: bradycardia, bronchoconstriction (nonselective)
Drugs that mimic the parasympathetic system:
Parasympathomimetic (cholinomimetic): “cholinergic drugs”
- Pyridostigmine: treats myasthenia gravis…cranial nerves that control eyes, facial muscles don’t contract like they should causing facial drooping and eye problems. This happens because there is a decrease in acetylcholine receptors, so muscles don’t perform properly. This medication provides more acetylcholine to help with maintaining normal muscle function.
Drug that stops the parasympathetic response (cause opposite effect) and lead to sympathetic response:
- Anticholinergic (parasympatholytic): block the neurotransmitter acetylcholine….stops parasympathetic response and mimics sympathetic response and can target various areas of the body
- Airway: “Ipratropium, Tiotropium” for asthma bronchodilation
- Atropine: increases heart rate in bradycardia episodes, eyes to dilate the pupil (ophthalmic atropine)
Side effects: dry mouth, urinary retention, constipation, increased heart rate
- Autonomic Nervous System – National Library of Medicine – PubMed Health. PubMed Health. Retrieved 16 November 2017, from https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0025455/
- Parasympathetic Nervous System – National Library of Medicine – PubMed Health. PubMed Health. Retrieved 16 November 2017, from https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0025459/