Coordination

Stimulus - Receptor - coordination - effector - response 

A stimulus is a change in an anima's surroundings and a response is a reaction to that change. 

RECEPTORS - 

Role - to detect the stimulus by changing its energy into the electrical ennergy of the nerve impulses. 

When energy is changed from one form to another , called - TRANSDUCTION. 

all receptors are transducers 

Nerve cell - Neurone, they are caused by movements of changed particles in and out of the neurone.

 Impulses from receptors pass alongnerves containing sensory neurones, until they reach the brain and spinal cord.

These two organs together, are known as - THE CENTRAL NERVOUS SYSTEM - CNS. 

Other nerves contain MOTOR NEURONES - transmit impulses to the muscels and glands.

AXON - fibre which carries impulses to the effector organ

Myelin Sheath - insulates axon - prevents short circuits with other axons - speeds up conduction of the impulses. 

Sclera - Tough outer coat/visible/white part of eye 

Cornea - transparent wondow/ lets light into eye Pupil - Hole/ lets light through 

Chlorid - contains pigment cells/stops light being reflected around inside eye. 

Retina - Light sensitive layer/ place where light energy is transduced into electrical energy of nerve impulses 

Rods + Cones - react to light/produces impulses in sensory neurones. SN pass impulses to Optic nerve - Rod calls cant distinguish different colours in dim light. Cone cells- only in bright light (Y) red,blue, green. 

Iris - Circular muscles - Radial muscles    

TO FORM AN IMAGE LIGHT NEEDS TO BE REFRACTED - takes place when light passes from one medium to another of a different density. IMAGE IS INVERTED (upside down)Brain interprets it the right wayup