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Upper motor neuron paralysis
A type of paralysis (loss of movement and/or sensation) that is due to injury or damage in the brain or spinal cord. This injury or damage in the brain or spinal cord causes damage to the cell body (the main part of the cell) and/or axons (the part of a nerve that sends a message) of the upper motor neurons. Upper motor neurons are neurons (nerve cells) in the motor cortex (an area of the brain located in middle, top part of the brain) that form pathways within the brain and from the brain to the spine.

In upper motor neuron paralysis, muscles are only affected in groups. Weakness occurs and so does paralysis, which is how this disorder got its name. Slight wasting away of muscles, tissues, and organs can occur from not using them, but sometimes no wasting away occurs at all. Another problem associated with upper motor neuron paralysis includes spasticity (involuntary muscle contractions) with hyperactive deep tendon reflexes (contracting muscles in response to a stretched muscle caused by a sharp tap). Spasticity is a condition in which there is increased tension in muscles that resist the force of gravity (the natural force that pulls objects downwards) as well as increased resistance to stretch.

Abnormal reflexes are present such as the Babinski reflex (when the big toe moves back and the other toes fan out after stroking the bottom of the foot) and Hoffman's reflex. Hoffman's reflex is when the end of the thumb and part of one or more of the other fingers flex in response to a sudden hard flick of the index, middle, or ring finger. Superficial reflexes (reflexes caused by stimulating the skin and not deeper areas) are absent. No muscle twitching occurs in upper motor neuron paralysis.

Compare upper motor neuron paralysis with lower motor neuron paralysis, a type of disorder that causes loss of movement and sensation due to injury or damage to lower motor neurons. A lower motor neuron is the part of a motor neuron (a type of nerve cell) that connects to the skeletal muscles. Skeletal muscles are muscles that are connected at either or both arms or legs with the skelton of the body.