Structures of the ANS Pathways Label each region of the sympathetic and parasympathetic divisions. ? View Available Hint(s) Preganglionic sympathetic axons Acetylcholine released from a postganglionic parasympathetic neuron at target tissue Spinal cord Preganglionic parasympathetic axon Heart Acetylcholine released between preganglionic and postganglionic neurons of the parasympathetic pathway Acetylcholine released between preganglionic and postganglionic neurons of the sympathetic pathway Peripheral ganglion Postganglionic parasympathetic axon Postganglionic sympathetic axons Norepinephrine released from a postganglionic sympathetic neuron at target issue Resat Help
The Correct Answer and Explanation is:
Here is the correctly labeled diagram. The labels are listed below, corresponding to their positions on the diagram.
Correct Labels:
- Topmost box (pointing to the long axon from the brain): Preganglionic parasympathetic axon
- Box on the left (pointing to the short axon from the spinal cord): Preganglionic sympathetic axon
- Box below the one above (pointing to the short axon to the heart): Postganglionic parasympathetic axon
- Bottommost box on the left (pointing to the neurotransmitter at the parasympathetic target): Acetylcholine released from a postganglionic parasympathetic neuron at target tissue
- Top box on the right (pointing to the parasympathetic ganglion synapse): Acetylcholine released between preganglionic and postganglionic neurons of the parasympathetic pathway
- Second box on the right (pointing to the sympathetic ganglion synapse): Acetylcholine released between preganglionic and postganglionic neurons of the sympathetic pathway
- Third box on the right (pointing to the sympathetic ganglion structure): Peripheral ganglion
- Fourth box on the right (pointing to the long axon to the heart): Postganglionic sympathetic axon
- Bottommost box on the right (pointing to the neurotransmitter at the sympathetic target): Norepinephrine released from a postganglionic sympathetic neuron at target tissue
Explanation
This diagram illustrates the fundamental structural and chemical differences between the sympathetic and parasympathetic divisions of the Autonomic Nervous System (ANS), both of which innervate the heart.
The ANS utilizes a two-neuron chain to connect the central nervous system (CNS) to target organs. This chain consists of a preganglionic neuron, whose cell body is in the CNS, and a postganglionic neuron, whose cell body is in a peripheral ganglion.
Parasympathetic Division (Top Pathway):
This division is often called the “rest-and-digest” system. As shown, its preganglionic neurons originate in the craniosacral regions of the CNS (the brainstem in this diagram). It is characterized by long preganglionic axons that travel almost all the way to the target organ, where they synapse in a ganglion. The postganglionic axons are therefore very short. At the ganglion, the preganglionic neuron releases acetylcholine (ACh). The postganglionic neuron also releases acetylcholine at the target tissue (the heart), typically slowing the heart rate.
Sympathetic Division (Bottom Pathway):
This is the “fight-or-flight” system. Its preganglionic neurons originate in the thoracolumbar region of the spinal cord. It features short preganglionic axons that synapse in a peripheral ganglion located relatively close to the spinal cord (part of the sympathetic chain). From this ganglion, a long postganglionic axon extends to the target organ. Similar to the parasympathetic division, the neurotransmitter released in the ganglion is acetylcholine (ACh). However, at the target tissue, most sympathetic postganglionic neurons release norepinephrine (NE), which typically increases heart rate and contractility. This distinct anatomy and neurochemistry allow the two divisions to exert opposing effects on the same organ, enabling precise autonomic control.
