Final answer:
A lesion involving the medial medulla and related medial lemniscus can cause contralateral loss of proprioception, vibration sense, and fine touch discrimination due to interference with the somatosensory pathway that runs through these structures.
Step-by-step explanation:
A lesion in the medial medulla that involves the medial lemniscus typically results in deficits to the somatosensory pathway, which can include loss of proprioception, vibration sense, and fine touch discrimination on the contralateral side of the body. The medial lemniscus is a fiber tract of the dorsal column system that extends from the nuclei gracilis and cuneatus to the thalamus, crossing over to the opposite side (decussates) at the level of the medulla. Therefore, a lesion here would affect the ability of sensory information to reach the thalamus and consequently the cerebral cortex for processing. This could lead to difficulties with spatial orientation and coordination as the brain is no longer receiving accurate information about the position and fine-touch sensory input of the contralateral side of the body.