Potenciacion

A STIMULI occurs when a living organism detects a change in their environment and responds to it. That stimuli is sensed by special cells called RECEPTORS. These receptors can be NEURONES: cellswhich can carry nerve impulses quickly along the body.
After the body has detected the stimuli, it sends a message to the motor neurons, which effect a reaction on the body.
The body is made up by aCENTRAL NERVOUS SYSTEM (consisting by the brain and spinal cord. It coordinates the messages travelling through the nervous system) and a PERIPHERAL NERVOUS SYSTEM (consisting of nerves and receptors).Reflex actions are fast and it automatically responses to a stimuli. They involve a series of neurons making up a reflex arc.
The most common is the SENSORY NEURON, in which the cell body islocated at the centre of its axon. It takes the impulse to the central nervous system and the motor neurone takes it to an effector. For example, automatically contracting the muscles on the arm, so that ittakes the hand out of the fire.
The RESEPTORS, is the part of an organism`s body which detects the stimuli. It is often part of the SENSE ORGAN (groups of receptor cells responding to specificstimuli: light, sound, touch, temperature and chemicals).
EYE
The receptor cells are located on the RETINA. They are called: ROD and CONE cells. The rod responds to dim light and cones to bright light,and they also give the colour vision. When the light is very bright, the circular muscle in the iris contracts, to protect the retina. When there is very little light, (dark room) the radial musclecontracts so it opens the iris and more light passes through the retina.
The cornea and lens focus light rays onto the fovea, the part of the aye where cone aells are most densely packed.
MUSCLESMuscles can pull when they contract, but they cannot push. A pair of muscles is therefore needed to pull in different directions
Hormones are chemicals made in endocrine glands and carried in the blood...