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Nerve cells(neurones)

The motor neurones carry impulses from the central nervous system to muscles and glands.The sensory neurones carry impulses from the sense organs to the central nervous system.The multi-polar neurones are neither sensory nor motor but make connections to other neurones inside the central nervous system.A nerve can carry many different impulses.These impulses will travel in one direction in sensory fibres and in the opposite direction in motor fibres.The fibres run inside the nerve.    Synapse:at a synapse,a branch at the end of one fibre is in close contact with the dendrite of another neurone.When an impulse arrives at the synapse,it releases a tiny amount of a chemical substance called neurotransmiters wich sets off an impulse in the next neurone.  The reflex arc.A reflex action is an automatic response to a stimulus.You cannot stop this reflex and you are not even aware that it is happening.The pathway of this reflex arc is hitting the tendon it streches the muscle and stimulates a strech receptor.The receptor sends off impulses in a sensory fibre.These sensory impulses travel in the nerve to the spinal cord.In the central region of the spinal cord,the sensory fibre passes the impuls eacross a synapse to a motor neurone wich conducts the impulse down the fibre,back to the thigh muscle and makes it contract and jerk the lower part of the limb forward.

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