The Nervous System



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The Nervous System





  • Structural Divisions

  • Functional Divisions

  • Neural Tissue


Structural Divisions





  • Central Nervous System (CNS) – consists of the brain and spinal cord

  • Peripheral Nervous System (PNS) – consists of all nerves and ganglia that lie outside the CNS


Central Nervous System (CNS)


  • The central nervous system includes the brain and spinal cord. The brain and spinal cord are complex organs, composed of neural tissue, blood vessels and various connective tissues.

  • The CNS is responsible for integrating, processing, and coordinating sensory information (internal and external conditions) and motor commands (control or adjust activities of the PNS).



Peripheral Nervous System (PNS)


  • Consists of cranial nerves that arise from the brain and spinal nerves that emerge from the spinal cord.

  • Sensory, or afferent, neurons are nerve cells delivers information to the CNS.

  • Motor, or efferent, neurons originate within the CNS and send information out to the muscles and glands.

  • The PNS can be divided into two subgroups: the Somatic Nervous System and the Autonomic Nervous System.


The Somatic Nervous System





  • SNS consists of sensory neurons that convey information from sense receptors to the CNS and motor neurons from the CNS that conduct impulses to skeletal muscles.

  • The SNS is voluntary because these motor responses can be consciously controlled.


The Autonomic Nervous System





  • The ANS consists of sensory neurons that convey information from receptors to the CNS and motor neurons from the CNS that conduct impulses to smooth muscle, cardiac muscle, and glands.

  • The ANS is unvoluntary because these motor responses are not consciously controlled.

  • The motor portion of the ANS consists of two branches: the Sympathetic Division and the Parasympathetic Division.


The Sympathetic and Parasympathetic Divisions of the ANS





  • The viscera, with few exceptions, receive instructions from both.

  • The two divisions typically have opposite actions. Processes promoted by the sympathetic neurons use energy, while processes promoted by the parasympathetic neurons restore/conserve energy.


Nervous Tissue





  • Neurons

  • Neroglia


Neuroglia





  • About half the space in the CNS is filled by neuroglia (“glue”).

  • Neuroglia isolate neurons, provide supporting framework for neural tissue, act as phagocytes, and help regulate composition of interstitial fluid.

  • There are four types of neuroglia in the CNS: Astrocytes, Oligodendrocytes, Microglia, and Ependymal Cells.


Astrocytes





  • “star cell”

  • Star shaped cells.

  • Participate in metabolism of neurotransmitters.

  • Maintain the proper balance of K+ for generation of nerve impulses.

  • Participate in brain development.

  • Help form the blood-brain barrier, which regulates the entry of substances into the brain.

  • Provide a link between neurons and blood vessels.


Oligodendrocytes





  • “few tree”

  • Smaller than astrocytes.

  • Form a supporting network by wrapping around neurons and producing a lipid and protein covering called a myelin sheath.



Microglia





  • “small glue”

  • Small, phagocytic neuroglia.

  • Derived from monocytes.

  • Protect the CNS from disease by engulfing invading microbes and clearing away debris from dead cells.



Ependymal cells


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