Autonomic System Background
To connect GPCRs to the Autonomic Nervous System, it is important to review foundational knowledge. You learned about the Autonomic Nervous System in anatomy.
Nervous System Organization
Source: physio-pedia.com.
The Autonomic Nervous System is part of the peripheral nervous system and is categorized into the parasympathetic nervous system, sympathetic nervous system, and enteric nervous system. Our focus will be on the parasympathetic and sympathetic nervous system.
Autonomic Nervous System Neurons
- The sympathetic and parasympathetic divisions of the autonomic nervous system are the two major efferent pathways controlling targets other than skeletal muscle.
- The sympathetic and parasympathetic divisions are innervate tissues by a two-synapse pathway.
The cell bodies of the first neuron reside within the central nervous system and are called preganglionic neurons. The preganglionic neurons are “found in columns of cells in the brainstem and spinal cord and send axons out of the CNS to make synapses with postganglionic neurons in peripheral ganglia interposed between the CNS and their target cells. Axons from these postganglionic neurons then project to their targets. The sympathetic and parasympathetic divisions can act independently of each other. However, in general, they work synergistically to control visceral activity and often act in opposite ways, like an accelerator and brake to regulate visceral function. An increase in output of the sympathetic division occurs under conditions such as stress, anxiety, physical activity, fear, or excitement, whereas parasympathetic output increases during sedentary activity, eating, or other ‘vegetative’ behavior.”
There are two neuron types in both the sympathetic and parasympathetic nervous systems.
- General visceral efferent neurons.
- Located in the central nervous system.
- Release acetylcholine.
- Stimulate N2 nicotinic receptors on postganglionic neurons.
- Located outside the central nervous system
- Release acetylcholine/norepinephrine/neuropeptides
Autonomic Nervous System Receptors and Physiologic Ligands/Transmitters
The sympathetic and parasympathetic nervous systems have different receptors and physiologic ligands/transmitters.
- All preganglionic neurons (both sympathetic and parasympathetic) release acetylcholine and stimulate N2 nicotinic receptors.
- All postganglionic PARASYMPATHETIC neurons release acetylcholine and stimulate muscarinic receptors on visceral organs.
- Most postganglionic SYMPATHETIC neurons release norepinephrine and stimulate adrenergic receptors on visceral organs.
- Sweat glands release acetylcholine and stimulate muscarinic receptors.
A note about this session
Sketch the autonomic nervous system preganglionic and postganglionic neurons for the sympathetic and parasympathetic nervous system.
Features of the parasympathetic and sympathetic nervous system.
Preganglionic and Postganglionic Receptors
Preganglionic Receptors (Nicotinic Receptors) and Physiologic Ligands (Neurotransmitters)
In the Autonomic Nervous System, the preganglionic physiologic ligand (neurotransmitter) is acetylcholine (ACh), and the preganglionic receptors are nicotinic (N2).
Nicotinic receptors are in the ligand-gated ion channel family.
Postganglionic Receptors (Adrenergic Receptors and Muscarinic Receptors) and Physiologic Ligands (Neurotransmitters)
Which Physiologic Ligands/Transmitters go with these neurons?
Acetylcholine
Norepinephrine
Acetylcholine
Acetylcholine
Acetylcholine
Acetylcholine
Which receptors go with these neurons?
Muscarinic
Image credits
Unless otherwise noted, images are from Adobe Stock.