Pharmacology - Introduction to Pharmacology

Pharmacology - Introduction to Pharmacology

Autonomic Nervous System (ANS)

  • Overview of ANS: The ANS controls involuntary bodily functions and is divided into three main components:

    • Sympathetic Division: Responsible for the 'fight or flight' response.
    • Parasympathetic Division: Responsible for 'rest and digest' activities.
    • Enteric Division: A network of neurons that governs the functions of the gastrointestinal system.

  • Divisions of the Nervous System:

    • CNS (Central Nervous System): Brain and spinal cord.
    • PNS (Peripheral Nervous System): All peripheral nerves, including sensory and motor divisions.

Key Concepts of ANS Functions

  • Functional Differences:
    • Sympathetic Actions:
    • Eye: Dilation of pupils (iris radial muscle contraction).
    • Heart: Increased heart rate and contractility.
    • Blood Vessels: Dilation in skeletal muscle; constriction in skin/mucous membranes.
    • Gastrointestinal Tract: Decreased motility and tone.
    • Parasympathetic Actions:
    • Eye: Contraction of the pupil (iris sphincter muscle contraction).
    • Heart: Decreased rate and contractility.
    • Gastrointestinal Tract: Increased motility and tone.

Cell Signaling in the ANS

  • Types of Signaling:

    • Autocrine: A cell signals to itself.
    • Paracrine: A cell signals to nearby cells.
    • Endocrine: A cell signals to distant cells through the bloodstream.

  • Neurotransmitter Release Process:

    1. Preganglionic Neuron: Originates in the CNS and synapses with postganglionic neurons.
    2. Postganglionic Neuron: Connects to the effector organ.
    3. Signal Transmission: Involves receptors and neurotransmitters (e.g., acetylcholine, norepinephrine).

Cholinergic System

  • Neurotransmitter: Acetylcholine (ACh)

  • Synthesis: Formed from choline and acetyl-CoA, catalyzed by choline acetyltransferase.

  • Degradation: Rapidly hydrolyzed by acetylcholinesterase (AChE).

  • Recycling:

    • Choline is taken back into the neuron after ACh breakdown.

  • Receptors:

    • Muscarinic Receptors: Subtypes M1-M5 found throughout the body affecting various functions (e.g., M3 stimulates glandular secretions).
    • Nicotinic Receptors: Located at neuromuscular junctions and autonomic ganglia.

Cholinergic Agonists and Antagonists

  • Agonists:

    • Direct-acting: Acetylcholine, pilocarpine, etc.
    • Indirect-acting (AChE inhibitors): Physostigmine, neostigmine.

  • Antagonists:

    • Atropine: Inhibits muscarinic receptors causing mydriasis, reduces secretions, increases heart rate.
    • Neuromuscular Blockers: Used in surgeries for muscle relaxation (e.g., succinylcholine).

Adrenergic System

  • Synthesis of Norepinephrine:
    • Rate-limiting step: Hydroxylation of tyrosine.
  • Release Mechanism: Adrenal glands release norepinephrine and epinephrine into the bloodstream during sympathetic stimulation.
  • Receptors:
    • Alpha (α) and Beta (β) Adrenoceptors:
    • α1: Vasoconstriction, increased blood pressure.
    • β1: Increased heart rate and contractility.
    • β2: Bronchodilation and vasodilation.

Adrenergic Agonists and Antagonists

  • Adrenergic Agonists (e.g., epinephrine, norepinephrine):
    • Stimulate the adrenergic receptors, leading to effects such as increased heart rate and bronchodilation.
  • Adrenergic Antagonists (e.g., prazosin, propranolol):
    • Block α or β receptors, used in treating various conditions like hypertension and arrhythmias.

Notable Side Effects of Adrenergic Drugs

  • Common Side Effects: Headaches, arrhythmias, tremors, nausea, and insomnia.

Conclusion

  • Overall Summary:
    • Understanding the ANS and its pharmacological agents is crucial for effective medical treatment of various conditions, focusing on both cholinergic and adrenergic systems. The interactions of these systems illustrate the delicate balance in physiological responses and therapeutic interventions.