The internal capsule is an area of the brain that is comprised of white matter. This white matter is a crucial part of the central nervous system, as it carries messages to the gray matter portions of the brain. The internal capsule is responsible for separating the thalamus as well as the caudate nucleus from the structure known as the lenticular nucleus.

The thalamus is a mass of grey matter in the brain that is responsible for motor function. The caudate nucleus assists with coordination as well as some body movements. The internal capsule works to separate these areas of the brain from the lenticular nucleus, a large area of grey matter within the brain. An axon is a type of fiber found inside of nerve cells called neurons. The axons found in the internal capsule are described as both ascending and descending.

The blood supply to the internal capsule comes from the lenticulostriate arteries. These vessels are branches of the middle cerebral artery. Due to the small size of these arteries as well as their location, they are particularly vulnerable to damage. This often occurs due to hypertension or vessel rupture.

A lacunar stroke is an example of a damaged artery affecting the internal capsule of the brain. This occurs when one of the arteries supplying blood to the internal capsule becomes blocked. Some reasons for this blockage include advanced age and diabetes. Studies also show that this type of stroke is more common among patients who smoke than in those who do not.

Hemiparesis, or weakness located on one side of the body, is a common symptom of a lacunar stroke. Partial paralysis can also become present in some cases. Physical and occupational therapy can often help the patient recover some of the lost functioning after the stroke. Depending upon the extent of the damage, surgical intervention is sometimes indicated.

Lesions on parts of the internal capsule can affect the connection between the brain stem and the cerebral cortex, called the corticobulbar tract. This region of white matter controls motor function in the neck, face and head. Depending on the area of the corticobulbar tract that is affected, damage can result in a loss of control over the upper facial muscles — eyebrows and forehead area — or the lower muscles — mouth and cheek area.

Prognosis following damage to the internal capsule of the brain depends upon the extent of the damage as well as the individual patient's response to treatment. It is essential to have a medical professional closely follow the patient's progress. It is not always possible for the patient to regain all of the lost functioning sustained from the injury, but with proper treatment, the quality of life can often be vastly improved.