Topic Overview

The nervous system is a complex, highly specialized network. It organizes, explains, and directs interactions between you and the world around you. The nervous system controls:

• Sight, hearing, taste, smell, and feeling (sensation).
• Voluntary and involuntary functions, such as movement, balance, and coordination. The nervous system also regulates the actions of most other body systems, such as blood flow and blood pressure.
• The ability to think and reason. The nervous system allows you to be conscious and have thoughts, memories, and language.

The nervous system is divided into the brain and spinal cord ( central nervous system , or CNS) and the nerve cells that control voluntary and involuntary movements ( peripheral nervous system , or PNS).

The symptoms of a nervous system problem depend on which area of the nervous system is involved and what is causing the problem. Nervous system problems may occur slowly and cause a gradual loss of function (degenerative). Or they may occur suddenly and cause life-threatening problems (acute). Symptoms may be mild or severe. Some serious conditions, diseases, and injuries that can cause nervous system problems include:

• Blood supply problems (vascular disorders).
• Injuries (trauma), especially injuries to the head and spinal cord.
• Problems that are present at birth (congenital).
• Mental health problems, such as anxiety disorders , depression , or psychosis .
• Exposure to toxins, such as carbon monoxide, arsenic, or lead.
• Problems that cause a gradual loss of function (degenerative). Examples include:
  • Parkinson's disease .
  • Multiple sclerosis (MS) .
  • Amyotrophic lateral sclerosis (ALS) .
  • Alzheimer's disease .
  • Huntington's disease .
  • Peripheral neuropathies .
• Infections. These may occur in the:
  • Brain ( encephalitis or abscesses ).
  • Membrane surrounding the brain and spinal cord ( meningitis ).
• Overuse of or withdrawal from prescription and nonprescription medicines, illegal drugs , or alcohol.
• A brain tumor .
• Organ system failure. Examples include:
  • Respiratory failure.
  • Heart failure.
  • Liver failure (hepatic encephalopathy).
  • Kidney failure (uremia).
• Other conditions. Some examples include:
  • Thyroid dysfunction ( overactive or underactive thyroid ).
  • High blood sugar ( diabetes ) or low blood sugar ( hypoglycemia ).
  • Electrolyte problems .
  • Nutritional deficiencies, such as vitamin B1 (thiamine) or vitamin B12 deficiency.
  • Guillain-Barré syndrome .

A sudden (acute) nervous system problem can cause many different symptoms, depending on the area of the nervous system involved. Stroke and transient ischemic attack (TIA) are common examples of acute problems. You may experience the sudden onset of one or more symptoms, such as:

• Numbness, tingling , weakness, or inability to move a part or all of one side of the body ( paralysis ).
• Dimness, blurring, double vision, or loss of vision in one or both eyes.
• Loss of speech, trouble talking, or trouble understanding speech.
• Sudden, severe headache.
• Dizziness, unsteadiness, or the inability to stand or walk, especially if other symptoms are present.
• Confusion or a change in level of consciousness or behavior.
• Severe nausea or vomiting.

Seizures can also cause sudden changes in consciousness, feeling (sensation), emotion, or thought. Abnormal body movements, such as muscle twitching, may or may not be present. How often the seizures occur and how severe they are depend on the cause of the seizures and the area of the brain involved. For more information, see the topic Seizures .

Diabetes can cause problems with balance, either as a result of peripheral neuropathy or stroke.

Vertigo and dizziness are problems of balance and coordination (equilibrium). Vertigo is often caused by a medicine or a problem of the inner ear or brain. Emotional distress, dehydration , blood pressure problems, and other diseases can all cause feelings of dizziness. For more information, see the topic Dizziness: Lightheadedness and Vertigo .

Most headaches are not caused by serious central nervous system problems. The pain that comes with a headache can range from a throbbing or a piercing pain, such as with a migraine , to severe pain that comes and goes over several days, such as with cluster headaches . Headaches are usually caused by problems with the sinuses, scalp, or muscles of or around the head. For more information, see the topic Headaches .

Check your symptoms to decide if and when you should see a doctor.