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

Homeostasis
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Terms in this set (25)
Homeostasis
Maintenance of a constant internal environment
Image: Homeostasis
Stimulus
A change from the normal condition
Image: Stimulus
Receptors
Organs in the body that detect changes in body conditions
Image: Receptors
Negative feedback
Reverse effect of a stimulus to restore the normal conditions of the internal environment
Image: Negative feedback
Vasoconstriction
Reduction in internal diameter of blood vessels in body to reduce the amount of blood flow
Image: Vasoconstriction
Vasodilation
Increase in internal diameter of blood vessels in body to increase amount of blood flow
Image: Vasodilation
Response (to a stimulus)
Reaction of an organism to a stimulus
Effectors
Organs or cells in the body that produce a response when stimulated by a nerve impulse
Image: Effectors
Synapse
Junction between two neurones or a junction between a neurone and an effector
Image: Synapse
Nerve impulse
Electrochemical signal
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