Final answer:
The correct ranking from largest to smallest relative amount of cortex devoted to control by the primary motor area is tongue, face, elbow, based on the motor homunculus representation of enervation and movement control. The correct option is (4)
Step-by-step explanation:
The question pertains to the ranking of body parts based on the relative amounts of cortex devoted to their control by the primary motor area. The correct order, as indicated by the motor homunculus, reflects that muscles which perform fine and agile movements possess a larger cortical representation than those responsible for coarser movements. Thus, the order from largest to smallest amount of cortical area devoted to their control would be: tongue, face, and lastly, elbow. This is because the tongue and facial muscles, especially those involved in speech and expressions, require more precise control than the elbow, which is typically associated with more general movements.
The primary motor cortex is structured in a topographical map closely mirroring the layout of the primary somatosensory cortex, forming a motor homunculus. The greater cortical space allocated to certain muscles is indicative of the fine movements and enervation they require. This is seen in the greater enervation of muscles in the hands, fingers, and lower face as compared to the less cortical space attributed to 'power muscles' like those in the buttock and back.
Based on this understanding, the correct ranking in terms of relative amounts of cortex dedicated to their control by the primary motor area is option 4) tongue, face, elbow.