The human body comprises about 650 different muscles, and all are under the control of the nervous system. The nervous system comprises billions of neurons, which are in spontaneous contact with each other for the aim of regulating and monitoring the sensory and internal activities.
The actions like leaning over to pick a pen incorporate the coordinated attempt of various groups of muscles. The conscious mind transfers this signal to the central nervous system that further translates it into electrical impulses.
These are then further transferred to the somatic component of the peripheral nervous system to the nerves accountable for monitoring the required muscles. With the arrival of a message, a chemical known as acetylcholine gets discharged from the nerve endings, instigating the muscle fibers membrane and making them a contract.