The brain, nerves and eyes GapFill

A typical reflex arc contains sensory, relay and  vehiclemotortransportactive neurones passing a signal from the sensory receptor to the effector. The brain is not involved in a reflex arc, and the coordinator in this case is always the  kidneysliverspinal cordheart.

The brain controls more complex behaviours, with the cerebellum controlling  facial recognitionfine motor controlspeechmemory, and the  cerebrummedulla oblongatahypothalamusbrain stem controlling basic functions, such as breathing and body temperature. Tumours in the brain are very difficult to treat because  the blood–brain barrierquadriplegiaa CT scana PET scan often prevents chemotherapy from working.

The eye is a sensory organ of the central nervous system. The receptor cells of the eye,  purines and pyrimidineshaploid and diploid cellsrods and coneshelices and pleated sheets, are found in the  cornearetinapupiliris, with light passing through the lens. Control of the  hardnessvolumethicknesscolour of the lens is how the eye focuses on distant or near objects. People who suffer from  long-sightednesscataractsquadriplegiashort-sightedness have trouble focusing on objects that are far away, but this can usually be corrected easily with  insulin injectionsimmunosuppressantsantihistaminesglasses.