Bundles of axons outside the central nervous system are referred to as spinal ______, whereas the bundles of axons inside the central nervous system are referred to as spinal ______.

Question

BlackTom AI · Accepted Answer

Bundles of axons in the peripheral nervous system are called nerves, while bundles of axons in the central nervous system are called tracts (or fasciculi).

1. Relevant knowledge points and concepts
- Nervous system divisions: central nervous system (CNS = brain and spinal cord) and peripheral nervous system (PNS = all neural tissue outside the CNS).
- Terminology for axon bundles: in the PNS a group of axons (with connective tissue sheaths) is called a nerve; in the CNS an analogous grouping of axons is called a tract (or fasciculus). The term "fibres" is more general (nerve fibres = axons) and not the standard anatomical name for a named bundle in these contexts.

2. Step-by-step reasoning
- The question contrasts location (outside vs inside the CNS) with the standard anatomical names for axon bundles.
- Outside the CNS → PNS → standard term: nerve (e.g., spinal nerves).
- Inside the CNS → CNS white matter → standard term: tract (e.g., corticospinal tract).

3. Intermediate steps / examples
- Spinal nerve: bundle of sensory and motor axons exiting the spinal cord into the periphery — called a nerve.
- Corticospinal tract: a pathway of descending motor axons inside the spinal cord/brainstem/CNS — called a tract.

4. Why the correct answer is correct
- The pair "nerves, tracts" matches the conventional anatomical nomenclature: PNS bundles = nerves; CNS bundles = tracts.

5. Why the other options are incorrect
- (a) "fibres, nerves": reverses and misuses terms — fibres is nonspecific and not the conventional name for PNS bundles; nerves are PNS, not CNS.
- (c) "tracts, nerves": swapped — tracts are CNS, not PNS; nerves are PNS, not CNS.
- (d) "nerves, fibres": second term is imprecise; CNS bundles are called tracts, not merely "fibres."

6. Conclusion
Therefore the correct choice is "nerves, tracts," which matches the provided answer.

Bundles of axons outside the central nervous system are referred to as spinal , whereas the bundles of axons inside the central nervous system are referred to as spinal .单项选择题

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Bundles of axons outside the central nervous system are referred to as spinal ______, whereas the bundles of axons inside the central nervous system are referred to as spinal ______.单项选择题