What cause the eye pupils to expand and contract?

Answers:    Its to let surrounded by light. It go small when there's too much light and immense when it starts to go threatening.
your pupils dilate [get bigger] when your iris opens out [the coloured module of your eyes] to let contained by smaller or greater amounts of light, so as not to sabotage the retina at the back of your eye.

these 'muscle contractions/expansions' are cause by light intensity, heartfelt reactions and can also be artificial by the use of drugs etc.
There are two muscles in your iris, a dilator and a sphincter muscle. Each of these have different innervation and responds to different stimuli. Everyone mentions light... i.e. one of the stimuli that triggers the sphincter muscle. Someone mentioned sexual arousal... its true, excitement of any type stimulates the sympathetic nervous system which activate the dilator muscle. In addition to hurricane lantern, excitement, medications, in attendance is also a constriction of the pupils when we focus on close objects. Also age... we lose sympathetic tone as we get elder. Therefore, we usually have larger pupils when we are young at heart as opposed to elderly. Hope this help and pardon the spelling errors.
Expand=Dilate. Contract=Constrict.

Here is a enumerate of some things that cause respectively.

Dilate: Low light conditions; some eye drops; looking up from a book to something i.e. far away; getting hit in the eye by a blunt be reluctant; becoming excited (see a previous answer); nerve mess up

Constrict: Bright lights; some eye drops; looking from a far away object to something i.e. 12-to-16 inches in front of you; inflammation inside of your eye; brashness damage (different brashness than the one mentioned for Dilate).
iris.it is the colored muscular diaphragm and have an opening call pupil through which light enter..when you are in really bright light, the iris expands and as a result the size of pupil decrease..and when you are in dim muted, the iris contracts, increasing the size of the pupil so that more light can enter.
change in reading light ^-^

when it's dark ur pupil get bigger casue it need to know how to take within as much light as possible

It get smaller in flimsy to prevent the pupil being shabby
Literally this is due to the effect of various stimuli on the iris, which act like the adjustable gap (aperture), of a camera.The most obvious of these is flimsy, but it also reacts to home, focusing on images at adjectives distances from the eye.
Light causes the pupils to expand and contract because the pupil is what absorb the light surrounded by your eye. It expands when there is minimal neutral because you need the most neutral to see clearly and contracts when your surroundings are bright as to dim the brightness. Other than light other things such as drugs can dispatch chemical messages to you brain that can result in effects such as dilated pupils.
the feathery.
its so weird, look at someone when the lights are turning on in that pupils will get dramatically smaller its reasonably scary..
the feathery around you.
bright light make them contract and dim light make them enlarge
Endorphine etc, etc XD
standard lamp and drugs
light, mortal high as kite, withdrawal of sleep and sexual arousal
When bright light is shone on the eye, it will automatically constrict. This is the pupillary reflex, which is an impressive test of brainstem function. Furthermore, the pupil will dilate if a human being sees an reason of interest, or if the amount of light is lowered.
Light and sexual arousal to designation two things.
They are light sensitive. The iris is a muscle which contracts and relaxes the muscle. The pupil shows how the muscle moves when subjected to feathery and dark

Drugs also engineer pupils apprear dilated, and apparently so does being attracted to someone
If in that is too much light your, pupils contract so smaller amount light is agree to in. If nearby is too little light your, pupils expand to tolerate in more insubstantial.
Sexual arousment, light, dread and some types of drugs.
some1 told me they do when you horny or angry

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