Coordination and control - The nervous system - Edexcel How the eye works
The nervous system enables humans to react to their surroundings and to coordinate their behaviour. It comprises billions of neurones, and it uses electrical impulses to communicate very quickly.
accommodationThe process of changing the shape of the lens of the eye to focus on near or distant objects. 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 which allows the light rays to refract (bend) more strongly.
To focus on a distant object - the lens is pulled thin which allows the light rays to refract slightly.
Position of object
Ciliary muscles
Suspensory ligaments
Muscle tension on lens
Lens shape
Refraction of light rays
Near
Contract
Slacken / loosen
Low
Fat / thicker
Light is refracted strongly
Distant
Relax
Stretched / tighten
High
Thin
Light is only refracted slightly
Position of object
Near
Ciliary muscles
Contract
Suspensory ligaments
Slacken / loosen
Muscle tension on lens
Low
Lens shape
Fat / thicker
Refraction of light rays
Light is refracted strongly
Position of object
Distant
Ciliary muscles
Relax
Suspensory ligaments
Stretched / tighten
Muscle tension on lens
High
Lens shape
Thin
Refraction of light rays
Light is only refracted slightly
Figure caption,
The lens changes shape to focus on near and distant objects