The short time after the first impulse arrives; the muscle is unable to respond to a second stimulus.
Reflex
Involuntary reaction in response to a stimulus that is conveyed to the CNS (Central Nervous System).
Red Reaction
Red coloration of the skin immediately after stroking the skin with a pointed object.
Red Blood Cell
Cell responsible for carrying oxygen in the blood; erythrocytes.
Rectum
Part of the digestive tract located between the sigmoid colon and the anal canal.
Receptor
Special molecule(s) located on the cell membrane that recognize and bind to a ligand. the specialized pair of a sensory neuron that responds to an external or internal stimuli is also known as a receptor.
Reactive Hypermia
Fiery red coloration seen soon after an occlusion to blood flow to the tissue is removed.
Radioisotope
An isotope that emits radioactive waves.