kopp Autonomic Nervous System and Pharmacology Review

Pharmacology Overview: Basic Neuroscience

  • Central Nervous System vs Peripheral Nervous System:

    • Central nervous system: Includes the brain and spinal cord.

    • Peripheral nervous system: Contains all nerves that extend from the CNS.

    • Differentiation between motor (signals from CNS) and sensory (signals to CNS) neurons.

  • Motor Neurons:

    • Sends signals to muscles or glands for action (e.g., moving the diaphragm via the phrenic nerve).

  • Sensory Neurons:

    • Sends signals from the body back to the brain (e.g., pain reception).

Overview of Autonomic Nervous System (ANS)

  • Divisions:

    • Sympathetic Nervous System (fight or flight)

    • Parasympathetic Nervous System (rest and digest)

  • Hierarchical Relationship:

    • Autonomic functions are subconscious and regulate involuntary body functions like heart rate, respiratory rate, and digestion.

Sympathetic Nervous System Details

  • Fight or Flight Response:

    • Activation of sympathetic nervous system leads to increased heart rate and respiratory rate:

    • Heart rate increase for blood flow and nutrient delivery to muscles

    • Bronchodilation for enhanced oxygen intake

  • Physiological Effects of Sympathetic Activation:

    • Increased contractility of the heart and elevated blood pressure.

    • Peripheral blood vessel constriction and muscle blood vessel dilation for prioritized blood flow.

    • Pupil dilation increases peripheral vision in a perceived threatening situation.

Parasympathetic Nervous System Details

  • Rest and Digest Response:

    • Activation typically leads to decreased heart and respiratory rates:

    • Heart rate decreases during states of calmness.

    • Bronchoconstriction occurs to limit airflow when it's not needed.

  • Physiological Effects of Parasympathetic Activation:

    • Peripheral blood vessels dilate while muscle blood vessels constrict.

    • Constriction of pupils improves focus on near objects.

Interaction of ANS with Pharmacology

  • Drugs Acting on the ANS:

    • Some drugs stimulate the sympathetic system, while others block the parasympathetic system.

    • Understanding drug action requires knowledge of targeted receptors (alpha/beta for sympathetic, muscarinic/nicotinic for parasympathetic).

Basic Neurotransmitters for Both Systems

  • Sympathetic System Neurotransmitters:

    • Main neurotransmitter is norepinephrine (also known as noradrenaline) which activates adrenergic receptors.

    • Adrenaline as a hormone is released into the bloodstream once the adrenal gland is stimulated.

  • Parasympathetic System Neurotransmitters:

    • Main neurotransmitter is acetylcholine at both preganglionic and postganglionic neurons.

    • Receptors:

    • Nicotinic receptors at the postganglionic neuron

    • Muscarinic receptors at the target organ level

Structure of ANS Neurons

  • Sympathetic and Parasympathetic Nervous Systems each consist of a two-neuron pathway.

    • Preganglionic neuron: originates in CNS, making contact at a ganglion

    • Postganglionic neuron: translates the signal to the targeted organ or gland

Receptor Types

  • Parasympathetic System receptors:

    • Muscarinic receptors present on target tissues.

  • Sympathetic System receptors:

    • Adrenergic receptors (alpha and beta types) on target tissues.

Aerosol Drug Administration Techniques

  1. Aerosol Particle Size Importance:

    • Particle size should be ideally between 1-5 microns for effective deposition in lower airways.

  2. Large Volume Nebulizers: Used for humidification and consist of larger droplet sizes (10 to 15 microns) for upper airway treatment.

  3. Modern Nebulizers:

    • Electronic devices like AeroGen produce uniform particle sizes for optimal lung delivery.

  4. Metered-Dose Inhalers: Require correct patient coordination to ensure delivery of medication deep into the lungs.

Recap on Drug Effects and Adverse Reactions

  • Importance of recognizing side effects of medications, particularly when interacting with the ANS, and understanding how they can lead to alterations in heart rate and respiratory functions.