$P$ nerve fibers transmit impulses from tissues/organs to the $CNS$ and $Q$ nerve fibers transmit regulatory impulses from the $CNS$ to the concerned peripheral tissues/organs.
$\quad\quad\quad P\quad\quad\quad Q$

• A
  Efferent nerve fibers $\quad\quad$ Efferent nerve fibers
• B
  Afferent nerve fibers $\quad\quad$ Afferent nerve fibers
• C
  Afferent nerve fibers $\quad\quad$ Efferent nerve fibers
• D
  Efferent nerve fibers $\quad\quad$ Afferent nerve fibers