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

Terms in this set (25)

Homeostasis
Maintenance of a constant internal environment
Stimulus
A change from the normal condition
Receptors
Organs in the body that detect changes in body conditions
Negative feedback
Reverse effect of a stimulus to restore the normal conditions of the internal environment
Vasoconstriction
Reduction in internal diameter of blood vessels in body to reduce the amount of blood flow
Vasodilation
Increase in internal diameter of blood vessels in body to increase amount of blood flow
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
Synapse
Junction between two neurones or a junction between a neurone and an effector
Nerve impulse
Electrochemical signal
Neurotransmitters
Chemicals which transmit nerve impulses across a synapse
Reflex action
Immediate response to a specific stimulus without conscious control
Voluntary action
Action that is controlled by conscious thought
Involuntary action
Action that is not under the control of will of an individual
Reflex arc
Shortest pathway by which nerve impulses travel from the receptor to the effector in a reflex action
Sense organs
Receptors which receive stimuli and inform the body of changes in the environment
Cones (in eye)
Photoreceptors which enable colour vision in bright light
Rods (in eye)
Photoreceptors which enable vision in dim light
Pupil reflex
Response of the pupil to different light intensities
Antagonistic muscles
Muscles which behave in opposing actions. When one set of muscles contracts, the other relaxes and vice versa.
Focusing
Adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina
Focal length
Distance between middle of lens and the point of focus on the retina
Hormones
Chemical substance produced in minute quantities by an endocrine gland and is transported in the bloodstream to target organ(s) where it exerts its effects
Endocrine glands
Ductless glands that secrete hormones directly into the bloodstream
Diabetes mellitus
Disease 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
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