Preganglionic neurons of the sympathetic nervous system play a crucial role in the body’s autonomic response, particularly during the “fight or flight” reaction. These neurons originate in the thoracic and lumbar regions of the spinal cord and send signals to postganglionic neurons that then innervate various target organs. A fundamental aspect of this communication is the neurotransmitter secreted by the preganglionic neurons.

Neurotransmitter Released by Preganglionic Sympathetic Neurons

The neurotransmitter secreted by the preganglionic neurons of the sympathetic nervous system is acetylcholine (ACh). These neurons release acetylcholine at the synapse within the sympathetic ganglia, where it activates nicotinic acetylcholine receptors on the postganglionic neurons.

Mechanism of Sympathetic Signal Transmission

Preganglionic neurons are relatively short and originate from the intermediolateral cell column of the spinal cord segments T1 to L2 or L3. Their myelinated axons travel to the sympathetic ganglia, either paravertebral or prevertebral, and synapse with the postganglionic neurons. At this synapse, acetylcholine is released, which binds to nicotinic receptors on the postganglionic neurons, exciting them and triggering the release of their respective neurotransmitters.

Postganglionic neurons typically release norepinephrine (noradrenaline) to effectors such as smooth muscles, cardiac muscles, and glands, except for some exceptions like sweat glands, which receive acetylcholine from postganglionic neurons. This two-step chemical signaling allows precise and regulated autonomic control.wikipedia+3

Common Misconceptions

• Epinephrine (adrenaline) is mainly secreted by the adrenal medulla directly into the bloodstream, not by sympathetic preganglionic neurons.

• Dopamine is a precursor of norepinephrine and also acts as a neurotransmitter but is not secreted by sympathetic preganglionic neurons.

• Norepinephrine is secreted by postganglionic, not preganglionic, sympathetic neurons.

Summary

To answer the question directly:

The neurotransmitter secreted by preganglionic neurons of the sympathetic nervous system is acetylcholine (2).