Paralysis is defined as the loss of muscle function in part of the body, which can be accompanied by a loss of sensation. This condition occurs when there is a disruption somewhere along the nervous system pathway that transmits signals from the brain to the muscles. Damage to its components prevents messages from reaching their intended muscular destinations. This interruption can be caused by various injuries or medical conditions that impair nerve and muscle function.
How Paralysis is Defined by Body Area
The most common way paralysis is classified is by the extent and location of the body affected, which gives rise to four primary types. The four types are monoplegia, hemiplegia, paraplegia, and quadriplegia.
Monoplegia is the paralysis that affects only one single limb, such as one arm or one leg. This type can sometimes be temporary, depending on the underlying cause.
Hemiplegia involves paralysis on one side of the body, typically affecting both the arm and the leg on the same side. This pattern is commonly observed following a stroke, where damage to one side of the brain affects motor control on the opposite side of the body.
Paraplegia is defined as the paralysis that impacts the lower half of the body, generally including both legs and sometimes the torso. This condition is frequently the result of a spinal cord injury occurring in the thoracic or lumbar regions of the spine.
Quadriplegia, also referred to as tetraplegia, is the most extensive form, affecting all four limbs and often the torso from the neck down. An injury high in the cervical section of the spinal cord usually causes this type of paralysis.
Neurological Events Leading to Paralysis
Paralysis is the direct result of damage to the central nervous system or the peripheral nervous system. Spinal Cord Injury (SCI) is one of the most frequent causes, often resulting from sudden trauma like car accidents or falls. The specific level of the vertebral column where the injury occurs determines which of the four types of paralysis will manifest.
A stroke, which is an interruption of blood flow to the brain, is another major cause, frequently leading to hemiplegia. Brain cells controlling movement in a certain area die, severing the communication pathway to the muscles. The location and size of the brain lesion dictate the extent of the resulting motor function loss.
Neurological diseases also contribute to paralysis by progressively damaging the nervous system. Multiple Sclerosis (MS) involves the immune system attacking the myelin sheath surrounding nerve fibers in the central nervous system, which slows or blocks nerve signals. Guillain-Barré Syndrome (GBS) is an autoimmune disorder where the immune system attacks the peripheral nervous system, often causing rapidly progressing, ascending weakness that can lead to temporary paralysis.
Characteristics of Paralysis Beyond Location
The condition is also described by the nature of the muscle involvement and the extent of the function loss. These secondary classifications provide further detail regarding the specific experience of the paralysis.
One distinction is between flaccid and spastic paralysis, which describes the muscle tone. Flaccid paralysis involves muscles that are weak and loose due to a loss of muscle tone, often caused by damage to the lower motor neurons connecting the spinal cord to the muscles. Conversely, spastic paralysis is characterized by muscles that are tight, stiff, and prone to involuntary jerks or spasms, typically resulting from damage to the upper motor neurons in the brain or spinal cord.
Another way paralysis is classified is by its completeness. Complete paralysis means there is a total loss of motor function and sensation below the level of injury. Incomplete paralysis, or paresis, indicates that some motor or sensory function is preserved below the injury site.
Paralysis may also be temporary or permanent, depending on the underlying cause. In many cases of GBS, individuals experience paralysis that resolves as the immune system attack subsides and the peripheral nerves begin to heal.