Autonomic Nervous System (ANS) Cheat Sheet

The Autonomic Nervous System (ANS) controls involuntary bodily functions through two opposing divisions: the sympathetic ('fight or flight') and parasympathetic ('rest and digest'). It utilizes a two-neuron chain and specific neurotransmitters to regulate organs and maintain homeostasis.

Core Principles

• ANS controls involuntary functions: smooth muscle, cardiac muscle, glands, adipocytes.
• Operates via a 2-neuron chain: preganglionic neuron, ganglionic neuron, target organ.
• Ganglia are the sites of synaptic transmission between neurons.
• Sympathetic division: 'fight or flight', generally increases activity.
• Parasympathetic division: 'rest and digest', generally decreases activity and conserves energy.
• Dual innervation: Most organs receive input from both divisions.
• Autonomic tone: Constant, low-level ANS activity maintains baseline function.
• Visceral reflexes: Automatic responses of organs, can be short (local) or long (CNS-involved).

Key Terms

• Autonomic Nervous System (ANS): Controls involuntary bodily functions like heart rate, digestion, and breathing.
• Sympathetic Division: Prepares the body for intense activity ('fight or flight').
• Parasympathetic Division: Promotes 'rest and digest' functions, conserving energy.
• Ganglia: Clusters of nerve cell bodies where synapses occur in the ANS.
• Autonomic Tone: The baseline level of ANS activity at any given time.
• Dual Innervation: When an organ receives input from both sympathetic and parasympathetic divisions.
• Visceral Reflex: An automatic response originating in an internal organ.

Timeline

• Origin: Sympathetic: T1-L2 spinal cord; Parasympathetic: Cranial nerves III, VII, IX, X and S2-S4 spinal cord.
• Ganglia Location: Sympathetic: Near spinal cord (chain, collateral) or adrenal medulla; Parasympathetic: Near or within target organ.
• Primary Neurotransmitter (Target Organ): Sympathetic: Norepinephrine (NE) and Epinephrine (E); Parasympathetic: Acetylcholine (ACh).
• Receptor Types: Sympathetic: Adrenergic (alpha, beta); Parasympathetic: Cholinergic (nicotinic, muscarinic).
• Control Center: Hypothalamus is the main control center for the ANS.