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Autonomic Nervous System Drugs:
Pharmacology and Medication
Autonomic Nervous System Drugs
Nervous System Review
The nervous system is divided into two main parts:
Central Nervous System (CNS): Consists of the brain and spinal cord, responsible for communication within the system. Peripheral Nervous System (PNS): Transmits messages between the CNS and the rest of the body.
The PNS is further divided into:
Somatic Nervous System (SNS): Responsible for voluntary functions, such as messages to skeletal muscles. Autonomic Nervous System (ANS): Responsible for involuntary functions, such as pupil dilation.
The ANS is divided into two divisions:
Sympathetic Division: Responsible for the "fight or flight" response, targeting adrenergic receptors (alpha and beta). Parasympathetic Division: Responsible for the "rest and digest" functions, targeting cholinergic receptors.
Sympathetic Division – Fight or Flight
The sympathetic division triggers the following responses:
Pupils dilate to increase visual ability. Salivation decreases, as it is a low priority. Heart rate increases to pump more blood and deliver more oxygen to tissues and muscles. Bronchioles dilate to allow more oxygen intake. Digestion is inhibited, as blood flow is diverted away from the digestive system. The liver stimulates the release of glucose for energy. The kidney secretes epinephrine and norepinephrine to stimulate the autonomic response. The bladder stores urine, as it is a low priority.
Parasympathetic Division – Rest and Digest
The parasympathetic division triggers the following responses:
Pupils constrict, as there is less need for visual acuity. Salivation is stimulated to aid in digestion. Heart rate decreases. Bronchioles constrict. Digestion is stimulated, including the stomach and gallbladder. Urination is reprioritized, and the bladder contracts. Sex organs are reprioritized.
Nervous System Drugs
Nervous system drugs are used to treat various conditions, such as pain, anxiety, insomnia, and involuntary muscle movements. They are classified into four main classes:
Adrenergics: Activate the sympathetic nervous system, producing a "fight or flight" response. Anti-adrenergics: Inhibit the sympathetic nervous system, producing the opposite of the "fight or flight" response (i.e., "rest and digest"). Cholinergics: Stimulate the parasympathetic nervous system, producing "rest and digest" symptoms. Anti-cholinergics: Inhibit the parasympathetic nervous system, producing the opposite of the "rest and digest" response.
Adrenergics
Adrenergic drugs mimic the natural catecholamines (stress hormones) epinephrine, norepinephrine, and dopamine. They act on alpha and beta cells at various sites, and some can be selective to certain sites to minimize adverse effects.
Major uses of adrenergics include:
Shock/hypotension: To increase blood pressure and heart rate. Asthma: To dilate bronchioles and improve breathing. Nasal congestion: To reduce nasal congestion.
Adverse effects of adrenergics include extensions of the "fight or flight" response, such as tachycardia, hypertension, and dysrhythmias, as well as CNS excitation, dry mouth, and anorexia.
Adrenergic medications include:
Adrenergic agonist inhalers (e.g., salbutamol) for acute bronchospasm. Non-selective adrenergics for glaucoma to dilate the pupil and decrease intraocular pressure. Vasopressors (e.g., norepinephrine) for shock to increase blood pressure. Adrenergic decongestants (e.g., Sudafed) in oral or intranasal forms.
Adverse effects of anti-cholinergics include erectile dysfunction, tachycardia, urinary retention, dry mouth/eyes, photophobia, altered sweating and temperature regulation, and possible sedation.
Anti-cholinergic medications include:
Urinary incontinence: Oxybutynin (Ditropan). Bronchospasm: Ipratropium bromide (Atrovent). Pre-operatively: To reduce respiratory secretions or aid in intubation. IBS and nausea: Due to decreased motility and peristalsis.
