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A nerve root is the base of a nerve at the point it exits the central nervous system. Once a nerve is outside the central nervous system, it branches to allow a number of smaller nerves to distribute information throughout the area of the body that is innervated by that nerve. Disorders involving the central nervous system can impact the nerve roots and individual nerve roots can also be affected by congenital conditions, trauma, and degenerative diseases that lead to impairments.
There are two types of nerve roots. Cranial nerve roots are found in the skull and they originate directly from the brain. There are 12 cranial nerve roots that innervate different areas of the face. The large number of nerves in the face are required to perform a number of important functions, from carrying visual information from the eye to controlling the muscles used for speaking and eating. Most of these nerve roots originate in the brainstem.
Spinal nerve roots originate in the spinal cord, emerging from between the vertebrae to supply different areas of the body. Each spinal nerve root is comprised of a dorsal nerve and a motor nerve that exit the vertebrae and then join up to create the nerve root. Ventral nerves contain motor neurons used for movement, while dorsal nerves have sensory neurons that convey sensory information to and from the brain.
In the case of spinal nerves, compression or fractures of the vertebrae can damage the nerve roots. This leads to symptoms like tingling, numbness, poor motor control, loss of sensation, and sometimes paralysis of the area of the body served by the nerve root. When the spine is fractured, severing the spinal cord, the nerve roots below the fracture can no longer communicate with the brain and the patient in turn will develop paralysis in the areas those nerves used to reach.
Problems that can develop at the nerve root include degenerative diseases that attack the nerves or the protective covering that sheathes them, along with damage caused by trauma. Brain injuries can lead to impaired communication between the brain and given nerve roots, leading to loss of sensation and other symptoms. When people develop neurological symptoms that indicate there is a problem in the nervous system, diagnostic testing is used to pinpoint the location of the problem so it can be addressed in treatment. This testing can include medical imaging, physical examinations, and electromyograms to study electrical conduction in the nerves.