[Campbell Biology P.1146] Based on Figure 49.17 and the accompanying text, which of the follo... | Practice Question

Based on Figure 49.17 and the accompanying text, which of the following statements best explains why the hand and face regions occupy a disproportionately larger area in both the primary motor and somatosensory cortices compared to, for example, the forearm or trunk?

  • A: The hand and face are larger body parts overall, requiring more cortical space.
  • B: Neurons in these regions receive and send more complex and detailed sensory and motor information.
  • C: These regions are located closer to the midline of the brain, making them easier to control.
  • D: The representation size is purely anatomical and does not correlate with functional importance.

Explanation

Figure 49.17 illustrates that the cortical surface area devoted to a body part is proportional to the density of sensory receptors and the complexity of motor control required for that part, not its physical size. The hands and face have a high density of sensory receptors e.g., for touch, fine discrimination and require very fine motor control e.g., for manipulation, facial expressions, speech , thus necessitating a larger representation in the somatosensory and motor cortices, respectively.