paralysis

DEFINITION
Paresis—weakness of voluntary movement
Paralysis—lack of voluntary movement
Quadriparesis (tetraparesis)—weakness of voluntary movements in all limbs
Quadriplegia (tetraplegia)—absence of all voluntary limb movement
Paraparesis—weakness of voluntary movements in pelvic limbs
Paraplegia—absence of all voluntary pelvic limb movement

PATHOPHYSIOLOGY
Weakness—may be caused by lesions in the upper or lower motor neuron system
Cell bodies or nuclei for the upper motor neuron system—located within the brain; responsible for initiating voluntary movement
Axons from these cell bodies—form tracts (rubrospinal, corticospinal, vestibulospinal, reticulospinal) that descend from the brain to synapse on interneurons in the spinal cord
Interneuronal axons—then synapse on large (a) motor neurons in the ventral gray matter of the spinal cord
Large motor neurons—cell bodies of origin for the lower motor neuron system, which is responsible for spinal reflexes
Collections of lower motor neurons in the cervical and lumbar intumescences—give rise to axons that form the ventral nerve roots, the spinal nerves, and (ultimately) the peripheral nerves that innervate limb muscles
Evaluation of limb reflexes—determine which system (upper or lower motor neuron) is involved
Upper motor neurons and their axons—inhibitory influence on the large motor neurons of the lower motor neuron system; maintain normal muscle tone and normal spinal reflexes; if injured, spinal reflexes are no longer inhibited or controlled and reflexes become exaggerated or hyperreflexic.
Large a motor neurons or their processes (peripheral nerves)—if injured, spinal reflexes cannot be elicited (areflexic) or are reduced (hyporeflexic).