Co-ordination in animals is achieved through the nervous system and the hormonal system
a change in environment is called a stimulus
a stimulus produces a response
in animals each type of stimulus is recognised by a receptor in the body
when a receptor is stimulated it causes an effector (muscle or hormone producing gland) to produce a response
a co-ordinator is needed to link between the receptor and the effector, usually brain or spinal cord - central nervous system
stimulus, change inside or outside body causing a change in behaviour
receptors, sense cells or organs which detect stimuli
co-ordinators, organs which receive info from receptors (brain or spinal cord)
effector, controlled by co-ordinators e.g. muscles and glands
response, behaviour resulting from original stimulus
each eye consists of an eyeball which sits in an orbit in the skull, the sides and back of the eyeball are thick and tough and is know as the 'white of the eye'
the front of the eye is transparent and is called the cornea
the cornea is covered by a membrane called the conjunctiva
the conjunctiva is moistened by tears, this is lubricating fluid produced by a gland under the eyelid, tears contain the enzyme lysozyme which kills bacteria
the pupil is the centre of the eye, it is the aperture of the eye, in bright light the pupil gets smaller to stop too much light getting into the eye and in the dark the pupil gets bigger to let more light in, controlled by the iris
the pupil is surrounded by the iris, the coloured part of the eye
the eyeball is held in place by muscles that can move the eye up and down and from side to side
the optic nerve runs from the back of the eyes to the brain, this nerve transmits impulses to the brain as to what is being seen
conjunctiva, a protective transparent covering that stops dust and dirt damaging the cornea and keeps cornea moist
cornea, transparent part of the sclera that allows light to enter
pupil, the opening in the middle of the iris through which light passes
iris, consists of radial and circular muscles that contract and relax to control the size of the pupil
lens, bends (refracts) light and focuses the light rays on the retina
retina, contains the receptor cells that are sensitive to light, the central part of the retina (fovea) contains a lot of light receptors
optic nerve, contains sensory neurones that link the retina to the brain, carries electrical impulses from the retina to the brain
the blind spot in the part of the retina where the optic nerve leaves (no image at this point and an image cannot be seen if it is focused on this part of the retina)
aqueous humour, maintains the correct pressure at the front part of the eye and it nourishes the cornea which has no blood vessels
vitreous humour, a jelly-like fluid which presses on the inner wall of the eyeball keeping it spherical
too much light can damage the cells in the retina
the muscles in the iris can contract or relax to change the size of the pupil, these muscles are called radial and circular muscles
dim light produces a large pupil (dilates) to get as much light as possible into the eye and to the retina
bright light reduces the size of the pupil (constricts) to reduce the amount of light entering the eye and falling on the retina
in dim light, circular muscles are relaxed and radial muscles are contracted, so the pupil dilates
in bright light, circular muscles are contracted and radial muscles are relaxed, so pupil constricts
when looking at an object light is reflected from the object and enters the eye
rays from the object pass through the cornea and lens they are bent inwards so that they can produce an image on the retina
the lens focuses the light rays so that they meet exactly on the retina, this is called refraction, the refraction of the light produces an image on the retina which is upside down
the cornea and lens are involved in focusing the light rays onto the retina
light rays from distant objects reparallel and don't need much refraction whereas rays from a near object need a lot of refraction
the lens of the eye can change shape in order to accommodate for near or far objects, this is called accommodation
the ciliary muscle (body) is a ring of muscle that surrounds the lens
the lens is attached to the ciliary muscle by suspensory ligaments, which are like small threads
the ciliary muscle can contract and relax and this will either make the suspensory ligaments tighter or slacker