Final answer:
Jonathan Keleher, who does not have a cerebellum, cannot effectively perform motor functions that involve coordination and fine-tuning, such as walking in a straight line or alternating movements, because the cerebellum is crucial for comparing and coordinating voluntary movements.
Step-by-step explanation:
Jonathan Keleher, one of the handful of people who have lived without a cerebellum, is not able to perform functions that require the coordination and fine-tuning of motor skills. The cerebellum is an important part of motor function in the nervous system; it is involved in procedural learning and acts as a comparator for voluntary movement. Without a cerebellum, tasks such as alternating movements, coordinating walking in a straight line, or any activities that require coordinating complex muscular actions become extremely challenging or impossible.
For example, walking in a straight line involves the primary motor cortex, proprioceptive and vestibular sensory feedback, as well as visual cues. The cerebellum coordinates these elements to ensure balance and movement accuracy, which would be compromised without it. Similarly, the coordination exams like the finger-to-nose test, which involve switching between antagonistic muscle groups, would be difficult for someone without a cerebellum due to the lack of communication and feedback planning between the motor cortex, pons, thalamus, and the cerebellar structure.