Sunday 10 April 2016

2.88 understand the function of the eye in focusing nearing distant objects, and in responding to changes in light intensity

By changing the shape of the lens the eye can focus on things near/far (this is known as accommodation). By changing the shape of the pupil the eye can adjust to different lighting intensities (e.g. see in bright light as well dim light).




    Near objects
    The ciliary muscle will contract (slackening the suspensory ligaments), this makes the lens appear more 'fat' (basically, its a little more curved).

    Distant objects
    The ciliary muscles relax and the suspensory ligaments contract, this makes the lens flatter

    Light intensity
    Bright light - triggers a reflex that makes the circular muscles contract causing radial muscles to relax, making the pupil smaller (allowing less light to enter so you don't get blinded). Light receptors detect bright light and send a message along a sensory neurone to an unconscious part of the brain, the message is passed onto a relay neurone that relays the message to a motor neurone which tells the circular muscle (the effector) in the iris to contract.

    Dim light - this triggers a reflex that makes the radial muscles contract and circular muscles relax, this makes the pupil bigger allowing more light to enter. This works as light receptors detect a dim light and send a message to the sensory neurone to an unconscious part of the brain, this message is then passed to a relay neurone which relays it to a motor neurone which tells the redial muscles (the effector) to contract.

    image source: midlandstech.edu

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