What happens when the brain and muscles lose connection?

Movement is an innate talent of human beings. However, some people lose their ability to move for various reasons. Their lives are confined to small rooms and sickbeds, and they cannot even take care of themselves in daily life.

Movement requires the brain, spinal cord, bones and muscles to work together. If there is a problem in any link, the nervous system and the motor system will be "disconnected" and the body will "be out of control". There are countless diseases that cause movement disorders, and here we will only give a brief overview.

Movement disorders originating from the brain are represented by Parkinson's disease and Huntington's disease.

Parkinson's disease is caused by the functional decline of dopaminergic neurons in the substantia nigra of the midbrain, which cannot inhibit cholinergic neurons in the striatum of the basal ganglia, resulting in increased muscle tension, muscle rigidity, reduced voluntary movement, slow movements, dull expressions, and static tremors. Parkinson's disease is a common neurodegenerative disease in the elderly, with a prevalence of 1% in people over 65 years old. The cause is still unclear, and it may be related to genetic and environmental factors. Imbalanced nutrition, alcoholism, trauma, overwork, and mental trauma can increase the risk of disease. Through drug treatment, intracranial implantation of electrodes or neural stem cell transplantation, the patient's condition can be controlled or improved.

Woody Guthrie, a famous American folk musician, was diagnosed with Huntington's disease. This is a rare genetic disease associated with a gene mutation on chromosome 4. The pathogenesis of Huntington's disease is opposite to that of Parkinson's disease. It is the functional decline of cholinergic neurons in the striatum, which leads to decreased muscle tone and subsequent involuntary dance-like movements. Patients have strange expressions, exaggerated movements, and unstable emotions, and are often discriminated against by people around them. In 2018, the first transgenic pig with the human Huntington's disease gene was born in a laboratory at Jinan University, helping scientists to study the pathogenesis of Huntington's disease in more depth.

Movement disorders originating from the spinal cord, such as poliomyelitis (commonly known as "polio"), are infectious diseases caused by viruses that once swept across Europe and North America. In severe cases, patients were paralyzed and unable to breathe. In 1928, Harvard University medical engineer Drinker invented an "iron lung". This 1,200-pound metal box only allowed the patient's head and neck to be exposed. Nurses used mechanical devices to push and pull the chest cavity to help seriously ill patients with respiratory paralysis breathe. With the promotion of polio vaccines, this disease is now almost extinct.

Mentioning Hawking, people will think of "A Brief History of Time" and the amyotrophic lateral sclerosis (ALS) that plagued him for most of his life. The disease manifests itself as damage to the motor neurons in the lateral cord of the spinal cord, and the brain cannot control the muscles through the spinal cord. Over time, the muscles gradually atrophy. The cause of the disease is still unknown. 20% of cases are related to genetic and gene defects, and the other 80% are affected by the acquired environment. Hawking became ill at the age of 21 and died at the age of 76. He used his thoughts on the stars in the universe to fight against the oppression of the body and achieve inner freedom.

Zhang Haidi suffered from spinal cord hemangioma when she was 5 years old, which caused her to be paralyzed from the waist down. Due to the transverse injury at the level of the second thoracic vertebra, the brain's motor commands could not pass through the paralyzed spinal cord, resulting in the inability to move the muscles below the chest. She practiced acupuncture, radio repair, and writing in a wheelchair, and she is a well-known example of a strong will despite physical disability in China.

Diseases of bones and muscles, such as osteomalacia, arthritis, and muscular dystrophy, can cause movement disorders. In our body, 639 large and small muscles are attached to 206 bones. One end of the muscle is attached to a bone, and the other end bypasses the joint and attaches to another bone. The contraction of the muscle drives the bones to cause movement. Disease and trauma can destroy the normal structure of bones and muscles, resulting in reduced mobility and indecent posture. Alfred Adler was an Austrian psychiatrist and founder of individual psychology. He suffered from rickets in his childhood and created classic psychological works such as "Inferiority and Transcendence" and "The Challenge of Mankind".

Bone and muscle lesions may also be caused by abnormalities in the circulatory and metabolic systems. The famous writer Shi Tiesheng suffered from vasculitis at the age of 21, and due to untimely treatment, his legs became paralyzed. Vasculitis is caused by vascular occlusion caused by spasm and thrombosis of small arteries, resulting in local ischemia of the limbs. In severe cases, blood vessels are blocked and muscles become necrotic. There are more than 2 million new stroke patients in my country every year, and many patients are left with varying degrees of hemiplegia. This is due to rupture or embolism of cerebral blood vessels, which causes ischemia and necrosis of some motor brain areas.

Movement disorders are a heavy blow to patients. Some people sink into despair, while others fight the disease with strong willpower and slowly recover or live tenaciously with the disease. They understand the value of health, cherish their hard-earned physical strength, and live a brilliant life.

(The author is an associate professor at Central China Normal University and a member of the Chinese Society of Neuroscience)