Final answer:
The axillary nerve is likely damaged if a patient cannot abduct the arm past 25 degrees, since this nerve innervates the deltoid muscle which controls arm abduction. The triceps brachii muscle extends the forearm, and upper motor neuron damage can impair voluntary control while preserving muscle tone.
Step-by-step explanation:
If a patient cannot abduct the arm past 25 degrees, the nerve that is probably damaged is the axillary nerve. Abduction of the arm is primarily controlled by the deltoid muscle, which is innervated by the axillary nerve. Damage to this nerve can result in an inability to fully abduct the arm.
The muscles and motions of the forearm are also important to consider when discussing nerve damage. For example, the triceps brachii is the muscle responsible for extending the forearm. Additionally, if a person has a motor disorder where they cannot move their arm voluntarily but their muscles have tone, it is usually an issue with the upper motor neurons. Upper motor neuron damage can preserve muscle tone but impair voluntary control.