Pharmacology Lecture: Autonomic Nervous System

Study Notes

Comprised of two main parts: Central Nervous System (CNS) and Peripheral Nervous System (PNS).
CNS includes the brain and spinal cord.
PNS includes cranial nerves, spinal nerves, somatic (voluntary) and autonomic (involuntary) nervous systems.

Parasympathetic Nervous System (Rest & Digest)
- Originates from the craniosacral regions: midbrain, medulla oblongata, and sacral spinal cord.
- Post-ganglionic fibers are short; ganglia are located close to or within innervated organs.
- Uses acetylcholine (Ach) which acts on nicotinic and muscarinic receptors.
Sympathetic Nervous System (Fight or Flight)
- Known as thoracolumbar outflow, originating from the thoracic and lumbar regions of the spinal cord.
- Long post-ganglionic fibers, as ganglia are near the spinal cord.
- Norepinephrine and epinephrine act on alpha and beta receptors.

Process involving neurotransmitter release from nerve terminals to specialized receptors on target cells.
Types of Nerves:
- Noradrenergic: Release norepinephrine.
- Adrenergic: Neurons releasing norepinephrine.
- Cholinergic: Neurons releasing acetylcholine.

Norepinephrine:
- Acts on alpha receptors (excitatory, e.g., α1, α2) and beta receptors (inhibitory, e.g., β1, β2).
- Alpha receptors are primarily found in vascular smooth muscle.
- Beta receptors influence heart activity and bronchial dilation.
Acetylcholine (Ach):
- Nicotinic receptors are excitatory.
- Muscarinic receptors have varied effects, such as excitation in cardiac tissue and inhibition in the gastrointestinal tract.

Sympathomimetics (Adrenergics): Stimulate the sympathetic nervous system.
Sympatholytics: Block sympathetic neurotransmission (receptor-blocking and neuronal-blocking).
Parasympathomimetics (Cholinergics): Stimulate the parasympathetic nervous system.
Parasympatholytics: Block parasympathetic neurotransmission.

Examples: Epinephrine, norepinephrine, isoproterenol.
- Vasoconstrictive effects in cutaneous, mucosal, renal, and mesenteric blood vessels.
- Small doses of epinephrine may cause vasodilation in coronary and skeletal blood vessels.

Dobutamine: Increases heart contractility without significant changes to heart rate or blood pressure; used for low output heart failure.
Fenoldopam: Acts on dopamine receptors for vasodilation; used for hypertension and renal protection.
Non-catecholamines: Ephedrine and its derivatives; affect the CNS and have various clinical applications.

Examples: Salbutamol, terbutaline, clenbuterol.
- Target β2 receptors for bronchodilation in asthma treatment.

Receptor-blocking Sympatholytics: Compete with norepinephrine for alpha and beta receptors; include ergot alkaloids and beta blockers (e.g., propranolol).
Neuronal-blocking Sympatholytics: Reduce norepinephrine levels directly; includes reserpine and guanethidine.

α-methyldopa: Produces a false transmitter while affecting norepinephrine uptake; used to treat hypertension.
Cocaine, imipramine: Inhibit norepinephrine reuptake; used as antidepressants.

Drugs are utilized for managing conditions like hypertension, angina, anxiety, asthma, and cardiac dysrhythmias.
Propranolol is noted for its wide-ranging effects on heart function and anxiety management.
Ocular therapies target fluid issues in glaucoma and achieve pupil constriction to facilitate fluid drainage.