Paralysis is the complete inability to move (impairment of motor function or locomotion) due to loss of muscular function for one or more muscle groups, caused by damage of the corresponding neuro-muscular apparatus.

Paralysis can cause excessive local sensation - hyperaesthesia, decreased local sensation - hypo-aesthesia or total loss of local sensation - anaesthesia in the affected area.

Paralysis may be localized or generalized, or it may follow a certain pattern.

For example, localized paralysis occurs in Bells' palsy where one side of the face may be paralyzed due to inflammation of the facial nerve on that side.

Patients with stroke may be weak throughout their body (global paralysis) or have hemiplegia (paralysis on one side of the body) or other patterns of paralysis depending on the area of damage in the brain.

Other patterns of paralysis arise due to different lesions and their sequelae. For example, lower spinal cord damage from a severe back injury may result in paraplegia (impairment in motor and/or sensory function of the lower extremities), while an injury higher up on the spinal cord, such as a neck injury, can cause quadriplegia or tetraplegia (all four limbs are paralyzed). Patients with paraplegia or quadriplegia often use equipment such as a wheelchair or standing frame for mobility and also in order to regain some independence.

Most paralyses caused by nervous system damage are constant in nature. However, there are forms of periodic paralysis, including sleep paralysis, which are caused by other factors.

Paralysis agitans is a progressive disorder of the nervous system marked by muscle tremors, muscle rigidity, decreased mobility, stooped posture, slow voluntary movements, and a mask-like facial expression. It is a progressive, degenerative neurologic disease characterized by a TREMOR that is maximal at rest, retropulsion (i.e. a tendency to fall backwards), rigidity, stooped posture, slowness of voluntary movements, and a masklike facial expression. Pathologic features include loss of melanin containing neurons in the substantia nigra and other pigmented nuclei of the brainstem. LEWY BODIES are present in the substantia nigra and locus coeruleus but may also be found in a related condition (LEWY BODY DISEASE, DIFFUSE) characterized by dementia in combination with varying degrees of parkinsonism.