It is further subdivided into sympathetic and parasympathetic divisions. The autonomic nervous system, also called the visceral efferent nervous system, supplies motor impulses to cardiac muscle, to smooth muscle, and to glandular epithelium. Because these nerves permit conscious control of the skeletal muscles, it is sometimes called the voluntary nervous system. The somatic nervous system, also called the somatomotor or somatic efferent nervous system, supplies motor impulses to the skeletal muscles. The efferent or motor division transmits impulses from the CNS out to the peripheral organs to cause an effect or action.įinally, the efferent or motor division is again subdivided into the somatic nervous system and the autonomic nervous system. The afferent or sensory division transmits impulses from peripheral organs to the CNS. The peripheral nervous system is further subdivided into an afferent (sensory) division and an efferent ( motor) division. Efferent motor neurons receive the signal from the interneuron and transmit it to the effector target cells, often muscle cells. Ganglia are collections, or small knots, of nerve cell bodies outside the CNS. The knee reflex is a good example of this. These are controlled by the reflex arc, which involves a sensory neuron bypassing the brain and sending a movement signal directly to the spinal cord to elicit a subconscious movement. Cranial nerves and spinal nerves extend from the CNS to peripheral organs such as muscles and glands. The somatic nervous system is responsible for the involuntary muscle responses or reflexes. Nerves are bundles of nerve fibers, much like muscles are bundles of muscle fibers. The organs of the peripheral nervous system are the nerves and ganglia. Although considered to be two separate organs, the brain and spinal cord are continuous at the foramen magnum. The brain is in the cranial vault, and the spinal cord is in the vertebral canal of the vertebral column. Because they are so vitally important, the brain and spinal cord, located in the dorsal body cavity, are encased in bone for protection. The autonomic nervous system is responsible for all. The brain and spinal cord are the organs of the central nervous system. The somatic nervous system is responsible for voluntary actions, namely the innervation of skeletal muscle. The nervous system as a whole is divided into two subdivisions: the central nervous system ( CNS) and the peripheral nervous system ( PNS). Each subdivision has structural and functional characteristics that distinguish it from the others. Although each subdivision of the system is also called a "nervous system," all of these smaller systems belong to the single, highly integrated nervous system. Sensory receptors are activated by a stimulus (change in the internal or external.
Acknowledgements Organization of the Nervous SystemĪlthough terminology seems to indicate otherwise, there is really only one nervous system in the body. The PNS includes sensory receptors, sensory neurons, and motor neurons.
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