The Human Nervous System
The human nervous system is responsible for sending, receiving and processing of nerve impulses. It controls the actions and feelings of all parts of the body and the mind, emotions and memory.
Located inside the skull, the brain is the primary organ of the nervous system. Without its protective envelope, the dura, brain weighs on average 1.4 kg, which represents 92% of the total weight of the central nervous system. The brain is connected to the upper end of the spinal cord (through the foramen magnum of the skull) and is responsible for the transmission of nerve impulses, processing of data transmitted by nerve impulses and the creation of process thought, at the highest level.
The spinal cord is one of the main parts of the central nervous system, serving as a kind of telegraph wire to relay signals from the brain to the peripheral structures of the body, and vice versa. Slightly flattened shape, its diameter is about half a centimeter. The spinal cord runs through the spinal canal formed by the vertebral arch and sends it to the periphery of the roots and branches like a tree. These structures contain bundles of nerve fibers that extend to the ends of the body, the fingertips to toes.
Nerve fiber is composed of a chain of neurons, which are the basic cells of the nervous system. Neurons are responsible for the receipt and transmission of nerve impulses and form for that long fibers interconnected. Neurons consist of a cell body, which contains a core, an axon and one or more dendrites from the cell body. Dendrites are the multi-branched portions that receive nerve impulses, while axons are elongated structures that transmit impulses from the cell body. The nervous system contains billions of neurons, which are so effective that a nerve impulse (for pain, for example) can be transmitted from the hand to the central nervous system and in the opposite direction to allow a reflex movement fraction of a second.