Which fiber type comprises ascending or descending long tracts connecting the cerebral cortex to deep brain structures, brainstem, cerebellum, and spinal cord?

• A. Association Fibers
• B. Projection Fibers
• C. Commissural Fibers
• D. Short Fibers

Answer: (B)

Projection fibers carry signals between the cerebral cortex and distant targets such as deep brain structures, brainstem, cerebellum, and spinal cord. They are long ascending or descending tracts that often pass through the internal capsule to reach their destinations. This sets them apart from association fibers, which connect regions within the same hemisphere; commissural fibers, which link corresponding areas across hemispheres; and short fibers (U-fibers), which connect nearby gyri. So the described long corticofugal and corticopetal pathways linking cortex to deep and distant centers are projection fibers.