Guided Study: Parasympathetic Fiber Pathways in the Autonomic Nervous System

Q: Does the illustration below show a parasympathetic or sympathetic fiber pathway? List two characteristics that helped you determine the correct answer.

Background

Topic: Autonomic Nervous System Fiber Pathways

This question tests your ability to distinguish between parasympathetic and sympathetic pathways based on structural and functional features of their neurons.

Key Terms and Concepts:

• Preganglionic neuron: The first neuron in the autonomic pathway, originating in the CNS.

• Postganglionic neuron: The second neuron, whose cell body is in a ganglion and whose axon innervates the target organ.

• Acetylcholine (ACh): A neurotransmitter released by both preganglionic and postganglionic neurons in the parasympathetic division.

• Myelination: Refers to the presence or absence of myelin on axons, affecting conduction speed.

Step-by-Step Guidance

1. Examine the diagram for the neurotransmitter released by both the preganglionic and postganglionic neurons. In the parasympathetic division, both release acetylcholine (ACh).

2. Observe the myelination of the axons. Parasympathetic preganglionic axons are lightly myelinated, while postganglionic axons are nonmyelinated.

3. Identify the length of the axons. Parasympathetic pathways typically have long preganglionic and short postganglionic fibers.

4. Compare these features to those of the sympathetic division, which usually has short preganglionic and long postganglionic fibers, and releases norepinephrine at the postganglionic synapse (except for sweat glands).

Try solving on your own before revealing the answer!

Final Answer:

This illustration shows a parasympathetic fiber pathway. Two characteristics that indicate this are: (1) both preganglionic and postganglionic neurons release acetylcholine (ACh), and (2) the preganglionic axon is lightly myelinated while the postganglionic axon is nonmyelinated.

These features are typical of the parasympathetic division, which is also called the craniosacral division.