GCE O Level Biology: Definitions of Keywords from Homeostasis, Nervous system, Eye and Hormones

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Terms in this set (25)
NeurotransmittersChemicals which transmit nerve impulses across a synapseReflex actionImmediate response to a specific stimulus without conscious controlVoluntary actionAction that is controlled by conscious thoughtInvoluntary actionAction that is not under the control of will of an individualReflex arcShortest pathway by which nerve impulses travel from the receptor to the effector in a reflex actionSense organsReceptors which receive stimuli and inform the body of changes in the environmentCones (in eye)Photoreceptors which enable colour vision in bright lightRods (in eye)Photoreceptors which enable vision in dim lightPupil reflexResponse of the pupil to different light intensitiesAntagonistic musclesMuscles which behave in opposing actions. When one set of muscles contracts, the other relaxes and vice versa.FocusingAdjustment of the lens of the eye so that clear images of objects at different distances are formed on the retinaFocal lengthDistance between middle of lens and the point of focus on the retinaHormonesChemical substance produced in minute quantities by an endocrine gland and is transported in the bloodstream to target organ(s) where it exerts its effectsEndocrine glandsDuctless glands that secrete hormones directly into the bloodstreamDiabetes mellitusDisease in which blood glucose concentration cannot be controlled within normal limits, usually due to low insulin production or failure of target cells to respond to insulin