A neurologist is a medical doctor who specializes in the diagnosis and treatment of conditions that affect the nervous system, which includes the brain, spinal cord, nerves, and muscles. Some of the most common problems that neurologists treat include:

1. Headaches: Migraine, tension headaches, and cluster headaches
2. Epilepsy: A disorder characterized by recurrent seizures
3. Stroke: A condition caused by a disruption of blood flow to the brain
4. Parkinson's disease: A progressive disorder of the nervous system that affects movement
5. Multiple Sclerosis (MS): A chronic disease that affects the central nervous system
6. Alzheimer's disease and other forms of dementia: Progressive disorders that affect memory and cognitive function
7. Peripheral neuropathy: A disorder that affects the nerves that carry information to and from the brain and spinal cord
8. Muscular dystrophy: A group of genetic disorders that cause progressive muscle weakness and wasting
9. Myasthenia gravis: An autoimmune disorder that causes weakness in the muscles that control movement
10. Sleep disorders: Neurologists can also diagnose and treat sleep disorders such as insomnia, narcolepsy, and sleep apnea.

These are some of the most common problems that neurologists treat, but there are many other conditions that can affect the nervous system. Neurologists work closely with other healthcare professionals, such as primary care physicians, neurosurgeons, and physical therapists, to provide comprehensive care for patients with neurological conditions.