pyramidal tract: any of the important motor nerves on each side of the central nervous system that run from the sensorimotor areas of the cortex through the brainstem to motor neurons of the cranial nerve nuclei and the ventral root of the spinal cord
hypersensitivity reaction: an inappropriate and excessive reaction to an allergen (as pollen or dust or animal hair or certain foods); severity ranges from mild allergy to severe systemic reactions leading to anaphylactic shock