Direction of impulses in sensory and relay neurons

Steps:

• Identify sensory neurons: transmit signals from sensory receptors to the CNS.
• Determine direction for sensory: impulses travel towards the CNS (option 2).
• Identify relay neurons: connect sensory and motor neurons within the CNS.
• Determine direction for relay: impulses travel within the CNS (option 3).

Why D is correct:

• Sensory neurons carry impulses towards the CNS by definition, while relay neurons process signals internally within the CNS.

Why the others are wrong:

• A: Sensory impulses do not travel away from the CNS; that's motor neurons.
• C: Relay impulses do not travel away from the CNS; they stay within it.

Final answer: D