2-4 Autonomics Function

Study Notes

Autonomic Nervous System (ANS) Overview

Comprises two divisions: Sympathetic (fight or flight) and Parasympathetic (rest and digest).
Sympathetic Division generally increases bodily activity (e.g., heart rate elevation and dilation of airways).
Parasympathetic Division typically decreases activity (e.g., heart rate reduction and constriction of airways).
Most organs receive dual innervation from both systems, exerting antagonistic effects.

Single Innervation Organs

Vasculature: Exclusively innervated by sympathetic fibers.
Sympathetic stimulation through α-receptors triggers vasoconstriction (smooth muscle contraction, reduced blood flow).
Weaker sympathetic stimulation can lead to vasodilation (relaxation of smooth muscle, increased blood flow).

Dual Innervation Examples

Heart Rate:
- Sympathetic stimulation via β1 receptors elevates heart rate.
- Parasympathetic activation through muscarinic receptors reduces heart rate.
Pupil Response:
- Sympathetic activation via α-receptors causes pupils to dilate (more light intake).
- Parasympathetic effects through muscarinic receptors cause pupil constriction (less light intake).
Bladder Control:
- Sympathetic effects inhibit bladder contraction, promoting filling.
- Parasympathetic effects stimulate bladder contraction, facilitating urination.

Special Cases

Horner Syndrome:
- Results from sympathetic fiber damage, leading to unopposed parasympathetic effects.
- Symptoms include ptosis (drooping eyelid), miosis (pupil constriction), and anhidrosis (lack of sweating).

Autonomic Drug Interactions

Muscarinic Agonists (e.g., Pilocarpine): Mimic parasympathetic effects, enhancing salivation and reducing heart rate.
Muscarinic Antagonists (e.g., Atropine): Block parasympathetic effects, leading to dry mouth and increased heart rate.
Adrenergic Agonists (e.g., Phenylephrine): Augment sympathetic stimulation, raising blood pressure and promoting vasoconstriction.
Beta-Blockers (e.g., Propranolol): Diminish sympathetic activity, decreasing heart rate and blood pressure.

Important Receptor Types

β1 Receptors: Primarily located in the heart (1 heart → β1).
β2 Receptors: Found in the lungs (2 lungs → β2).
α-Receptors: Generally facilitate vasoconstriction (smooth muscle contraction).

Salivation (Dual Innervation, Cooperative Response)

Parasympathetic Activation: Increases watery saliva during rest and digestion.
Sympathetic Activation: Triggers thick, enzyme-laden saliva, associated with stress-related dry mouth.

Central Control

Hypothalamus: Acts as the primary regulatory center for both divisions of the ANS, coordinating through the brainstem and spinal cord.

Potential Exam Topics

Distinction between single and dual innervation examples.
Comparative effects of sympathetic and parasympathetic on the heart, eyes, bladder, and vasculature.
Mechanism and implications of Horner Syndrome.
Effects of autonomic drugs (agonists and antagonists) on the sympathetic and parasympathetic systems.
The role of the hypothalamus in autonomic control.

Description

This quiz covers the fundamental concepts of the Autonomic Nervous System (ANS), including its two primary divisions: sympathetic and parasympathetic. It explores their roles in regulating bodily functions such as heart rate and blood flow, as well as examples of single and dual innervation of organs.