Final answer:
The hypoglossal nerve is responsible for controlling the muscles of the tongue and a test involving sticking out the tongue can help identify any deficits. Upper motor neuron lesions can cause various features such as muscle weakness and a positive Babinski sign, while lower motor neuron lesions may result in contralateral tongue deviation.
Step-by-step explanation:
The hypoglossal nerve is the motor nerve that controls the muscles of the tongue, except for the palatoglossus muscle, which is controlled by the vagus nerve. The hypoglossal nerve test involves asking the patient to stick out their tongue, and if there is a deficit in one side of the nerve, the tongue will point to that side. Tongue deviation can indicate damage or a lesion in the hypoglossal nerve or its associated structures.
In terms of the features of upper versus lower motor neuron lesions, upper motor neuron lesions may cause muscle weakness, strong deep tendon reflexes, decreased control of movement, slowness, spasticity, pronator drift, a positive Babinski sign, and the clasp-knife response. Lower motor neuron lesions, on the other hand, can result in contralateral tongue deviation.