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The Nervous System and Responding to Stimuli.

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´╗┐Coordination and Response The Nervous System and Responding to stimuli Organism need to respond to their environment to survive: Animals increase their chances of surviving by responding to change in their external environment like shivering in the cold. Animals also change their internal environment to make sure conditions are right for the entire metabolism. Plants increase survival chances by responding to changes in the environment. Any change in internal and external environment is stimuli. Receptors and Effectors * Receptors detect stimuli; these receptors are found in sense organs like eyes and ears for example cone cells in the eyes detect light change. * Effectors are the cells that bring about a response from the stimuli such as the muscle cells and hormonal gland cells. * They communicate using the nervous and hormone systems. The Central Nervous System (CNS) Your nervous system is made up of sensory, motor and relay neurones. The CNS is your Spinal cord and Brain only. ...read more.


Cone cells are found all in the retina but there are loads in the fovea The optic nerve is where the message is sent to the brain. https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcR8ydCmJ9vyW5VBcTg3VkEYj4NhWQKegF0gWTEf5OtCG0d_1GMu Iris Reflex It bright light the circular muscle contract so more of the retina is covered, in dim light the circular muscles relax so less of the retina is covered so the pupil is bigger and you can see more clearly. Focusing on near and far things To focus on things far we make the lens thin by contracting ciliary muscles, which to look at close things we relax the ciliary muscles so the lens is fat. Diagram of visual accommodation Long sighted people are unable to focus on near things so it makes it blurry, this can be corrected by putting a thin glass in front. Short sighted people are unable to focus on distant objects. This is fixed by putting some thick and fat glass in front. Hormones Hormones are chemical messages sent in the blood: Hormones are chemically released in the blood and are carried by blood plasma, they travel around the whole body but only effect target cells. ...read more.


The Skin plays an important role in maintaining body temperature: When you?re Hot: Lots of sweat produced as when it evaporates it transfers heat away so it cools you down. The blood vessels close to the surface widen so you lose more heat The hairs lie flat. When you?re cold You don?t sweat as much Vasodilation happens so no water near the top so the blood doesn?t lose a lot of heat Shiver so you respire so more so heat is created. Hairs stand up so it creates an insulating layer to keep air to keep you warm. Smaller Organisms cool down quicker http://www.sciencebuddies.org/Files/3834/5/PlantBio_img032.jpg * Smaller organism have bigger surface area to volume ratio * Lose heat much more quicker and gain heat much more quickly. Response in Plants Plants have stimuli as well. They can sense the direction of light through the use of auxin. When a shoot is exposed to light it accumulates on the other side and auxin makes the plant grow so it moves the plant towards the light. The plant shoots are negatively geotropic so they grow opposite gravity. The roots are positively geotropism so they grow towards the ground. ...read more.

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