A neurologist is a physician who diagnoses and treats disorders of the nervous system which is comprised of the brain, spinal cord and nerves. These doctors do not perform surgery, but refer patients to neurological surgeons when they determine that surgical intervention is necessary.
Some of the conditions that neurologists diagnose and treat are epilepsy, aneurysms, hydrocephalus, Parkinson's disease, multiple sclerosis, stroke, spinal disc herniation, and spinal disease.
In addition to using diagnostic tests like MRI, CT scans, EEG and EMG, neurologists also employ neurological testing to gauge muscle strength and movement, balance, reflexes, sensation, memory, speech, and other cognitive abilities.

An addiction medicine specialist is a doctor who treats patients with addictions to substances like drugs and alcohol or, in some cases, behaviors like gambling. Many of these specialists also treat the diseases that stem from these addictions.
These physicians are specially trained to prevent and treat the disease of addiction via psychiatric means, or other fields of medicine like family or internal medicine.

A general practitioner is similar to a family practitioner in that they treat patients of all ages with a variety of health concerns. These doctors treat everyday ailments, some acute and chronic diseases, and also provid health checkups, physicals, inoculations and preventative care.
General practitioners differ from family practitioners because they are not required to complete an additional residency in family medicine after completing their medical school residency. Like family practitioners, general practitioners will also provide referrals to patients who are in need of a specialist.

A neurological surgeon is a physician who surgically treats disorders of the nervous system, which is comprised of the brain, spinal cord and nerves.
In addition to treating trauma of the head and spine, these doctors also treat disorders like epilepsy, aneurysms, hydrocephalus, Parkinson's disease, multiple sclerosis, stroke, spinal disc herniation, and spinal disease.
Neurological surgeons can perform surgical procedures on the brain, such as stereotactic surgery, microsurgery, endoscopic surgery, stereotactic radiosurgery, and endovascular image guided methods.

An internist is a physician who focuses on the diagnosis and treatment of conditions that affect the adult population—both acute and chronic.
These doctors are often who adults see as their primary physicians because they treat a broad range of illnesses that do not require surgical or specialist interventions. They also work to help a patient maintain optimal health in order to prevent the onset of disease.
In addition to treating the common cold and flu, internists also treat chronic diseases like diabetes and heart disease.