What Is an Upper Motor Neuron Injury?

A neuron is an essential part of the body’s nervous system. It is responsible for communication between the brain and the body, allowing the body to respond quickly and efficiently to changes in the environment through electrical and chemical impulses or signals. An upper motor neuron carries motor or movement signals from the brain to the spinal cord where they are then transmitted to a lower motor neuron to be carried to the appropriate part of the body. An upper motor neuron injury, also referred to as a lesion, is any type of damage to one of these nervous system components, resulting in interruption of this messenger service.

Upper motor neuron syndrome, an upper motor neuron injury, can affect the part of the body associated with the area of damage. Common symptoms can include paralysis and spasticity. Paralysis is the inability to move a part of the body. Spasticity, also known as hypertonia, is a condition where the muscles are unusually and consistently tight or rigid. This is caused by a constant firing of the muscle cells causing spasms or involuntary contractions which commonly are resistant to an external force attempting to break the pattern or move the affected limb.

When the body sustains an upper motor neuron injury it inhibits the body from responding appropriately. This can be evident by the presence of a positive Babinski reflex. The Babinski reflex is a normal reaction of the toes stretching up and out in response to a firm stroke to the soles of the feet in young children under the age of two. If an upper motor neuron injury has been experienced, this reflex often returns. This change in this reflex can be temporary or permanent, depending on the nature and severity of the injury or damage sustained to the nervous system.

The areas of the body affected by such an injury correspond to the area damaged. Injuries that can cause a motor neuron lesion can include a traumatic brain injury where the brain is harmed by a severe blow to the head, or a cerebral vascular accident (CVA) where there is a break or rupture of a blood vessel in the head causing the brain to be saturated or engulfed with excessive blood. Some medical conditions, such as cerebral palsy, a movement disorder caused by abnormal brain development or a brain injury before birth, or seizure disorders, a condition marked by irregular firing of nerve cells may also cause a upper motor neuron injury.