Answer :
Final answer:
The correct statement is Option A: Motor pathways cross over as they descend (decussate), and auditory pathways cross over as they ascend (decussate) within the central nervous system. This understanding is essential for comprehending how the brain processes motor commands and auditory information.
Explanation:
The correct statement related to the decussation of motor and auditory pathways is Option A: Motor pathways decussate as they descend, and auditory pathways decussate in ascension. The motor output, including the ones from the primary motor cortex, follows two main descending pathways: the corticobulbar and corticospinal tracts. The axons of the corticobulbar tract are ipsilateral, while the axons of the corticospinal tract mostly decussate, meaning they cross over to the opposite side of the body. Therefore, the right motor cortex controls the muscles on the left side of the body and vice versa.
The ascending auditory pathway is complex and involves several brainstem nuclei such as the cochlear nuclear complex and superior olivary complex, before travelling to the inferior colliculus and eventually reaching the medial geniculate nucleus of the thalamus. From the thalamus, it proceeds to the primary auditory cortex in the temporal lobe. This information further bifurcates into dorsal and ventral streams for processing 'where' and 'what' aspects of sound, respectively. Unlike motor pathways, auditory pathways cross sides (decussate) as they ascend in the central nervous system.
In summary, motor pathways cross as they descend from the brain, and the auditory pathways cross as they ascend within the central nervous system.
