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Nervous System and Spinal Cord



The nervous system senses changes within the body and in the environment. It communicates these changes with the rest of the body. The nervous system includes nerve cells, called neurons and neuroglial cells. Neurons propagate signals, while neuroglia provide structural and metabolic support. The nervous system can be anatomically divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The central nervous system consists of the brain and spinal cord, while the peripheral nervous system includes neurons that travel both away from and toward the brain. Neurons of the peripheral nervous system are further divided based on function. For example, motor neurons are part of the somatic nervous system and help out with body movement. The body also has an enteric nervous system, part of the autonomic nervous system within the PNS, which supports the gastrointestinal tract. This system works with the CNS to control many of the involuntary functions in the gastrointestinal tract, such as digestive processes and gut motility.

At A Glance

  • The nervous system is anatomically divided into the central nervous system (CNS), which consists of the brain and spinal cord, as well as the peripheral nervous system (PNS), which consists of neurons and neuroglia that travel to and away from the brain and spinal cord.
  • A neuron consists of three parts: a cell body that contains the nucleus, dendrites attached to the cell body that receives signals, and the axon that plays a role in the propagation of these signals.
  • Neurons differ based on function (afferent, efferent, interneurons) and structure (multipolar, bipolar, unipolar, anaxonic), which is defined by the number and type of projections extending from the cell body.
  • Oligodendrocytes, ependymal cells, microglia, and astrocytes are neuroglia found in the CNS, while Schwann cells and satellite cells are neuroglia found in the PNS.
  • Spinal nerves are parts of the peripheral nervous system and carry motor, sensory, and autonomic signals between the spinal cord and the rest of the body.
  • Nerve impulses are electrical signals that propagate via action potentials and occur when there is a change in the electrical potential of the neural membrane.
  • Neurons communicate with one another using electrical and chemical signals via junctions called synapses.
  • Reflexes are fast, unpredictable, involuntary reactions to an external stimulus.
  • The sympathetic nervous system increases the activities of the body to be more alert and excited, while the parasympathetic nervous system regulates actions that do not require a fast response.