The Nervous System is the system of cells, tissues, and organs that regulates the body's responses to internal and external stimuli. In vertebrates it consists of the brain, spinal cord, nerves, ganglia, and parts of the receptor and effector organs.
Your nervous system is composed of the central nervous system, the cranial nerves, and the peripheral nerves. The brain and spinal cord together form the central nervous system. The cranial nerves connect the brain to the head. The four groups of nerves that branch from the cervical, thoracic, lumbar, and sacral regions of the spinal cord are called the peripheral nerves.
The peripheral nervous system consists of sensory neurons running from stimulus receptors that inform the Central Nervous System of the stimuli. It also consists of motor neurons running from the Central Nervous System to the muscles and glands, called effectors, which take action. The peripheral nervous system is further subdivided into an sensory division and an motor division. The sensory division transmits impulses from peripheral organs to the Central Nervous System. The motor division transmits impulses from the Central Nervous System out to the peripheral organs to cause an effect or action. The Somatic nervous system of the motor division supplies motor impulses to the skeletal muscles. Because these nerves permit conscious control of the skeletal muscles, it is sometimes called the voluntary nervous system. The autonomic nervous system supplies motor impulses to cardiac muscle, to smooth muscle, and to glandular epithelium. Because the autonomic nervous system regulates involuntary or automatic functions, it is called the involuntary nervous system.
The brain is the source of all our behavior, thoughts, feelings, and experiences. In humans, the brain weighs about 3 pounds. Differences in weight and size don't have anything to do with differences in mental ability. The brain is a pinkish mass that is composed of about 10 billion...
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