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Coordination and control - The nervous system - AQA How the eye works – Higher

The nervous system enables humans to react to their surroundings and to coordinate their behaviour. It comprises millions of neurones and uses electrical impulses to communicate very quickly.

Part of Biology (Single Science)Homeostasis and response

How the eye works – Higher

Accommodation is the process of changing the shape of the lens to focus on near or distant objects.

To focus on a near object – the lens becomes thicker, this allows the light rays to refract (bend) more strongly.

To focus on a distant object – the lens is pulled thin, this allows the light rays to refract slightly.

PositionCiliary musclesSuspensory ligamentsMuscle tensionLens shapeRefraction
NearContractSlacken/loosenLowFat/thickerLight is refracted strongly
DistantRelaxStretched/tightenHighThinLight is only refracted slightly
PositionNear
Ciliary musclesContract
Suspensory ligamentsSlacken/loosen
Muscle tensionLow
Lens shapeFat/thicker
RefractionLight is refracted strongly
PositionDistant
Ciliary musclesRelax
Suspensory ligamentsStretched/tighten
Muscle tensionHigh
Lens shapeThin
RefractionLight is only refracted slightly
Diagram showing how an image focuses at the retina
Figure caption,
The lens changes shape to focus on near and distant objects