NERVOUS SYSTEM

• The nervous system includes various organs
• Organs included in the nervous system

  • Brain and spinal cord
  • Receptors of sense organs (eyes, ears, etc.)
  • Nerves that connect to other systems
• Nervous tissue


  • Contains two kinds of cells
  • Neurons for intercellular communication
  • Neuroglia (glial cells) essential to survival and function of neurons
• Neurons


  Basic functional units of the nervous system that send and receive signals
• Neuroglia


  Support and protect neurons
• Anatomical divisions of the nervous system

  • Central nervous system
  • Peripheral nervous system
• Central nervous system (CNS)

  • Consists of brain and spinal cord
  • Processes and coordinates sensory data
  • Controls activities of peripheral organs
  • Higher functions include intelligence, memory, learning, and emotion
• Peripheral nervous system (PNS)


  • Includes all nervous tissue outside CNS
  • Delivers sensory information to the CNS
  • Carries motor commands to peripheral tissues
• Nerves (peripheral nerves)


  • Bundles of axons with connective tissues and blood vessels
  • Carry sensory information and motor commands
  • Cranial nerves connect to brain
  • Spinal nerves attach to spinal cord
• Cell body (soma)


  • Contains large nucleus and nucleolus
  • Contains perikaryon (cytoplasm)
  • Contains mitochondria (produce energy)
  • Contains RER and ribosomes (synthesize proteins)
• Dendrites


  • Short and highly branched processes extending from cell body
  • Receive information from other neurons
• Axon


  • Single, long cytoplasmic process that propagates electrical signals (action potentials)
• Axoplasm


  Cytoplasm of axon
• Structures of the axon

  • Axolemma (plasma membrane of the axon)
  • Initial segment (base of axon)
  • Axon hillock (thick region that attaches initial segment to cell body)
  • Collaterals (branches of the axon)
  • Telodendria (fine extensions of distal axon)
  • Axon terminals (synaptic terminals)
• Axonal (axoplasmic) transport is the movement of materials between cell body and axon terminals
• Structural classification of neurons

  • Bipolar neurons
  • Unipolar neurons (pseudounipolar neurons)
  • Multipolar neurons
• Bipolar neurons


  • Small and rare; One dendrite and one axon; Found in special sense organs (sight, smell, hearing)
• Unipolar neurons


  • Axon and dendrites are fused; Cell body to one side; Most sensory neurons of PNS
• Multipolar neurons


  • Have one long axon and two or more dendrites; Common in the CNS; All motor neurons that control skeletal muscles
• Functional classifications of neurons

  • Sensory neurons
  • Motor neurons
  • Interneurons
• Sensory neurons (afferent neurons)


  • Unipolar; Cell bodies grouped in sensory ganglia; Processes extend from sensory receptors to CNS
• Somatic sensory neurons


  • Monitor external environment
• Visceral sensory neurons


  • Monitor internal environment
• Motor neurons (efferent neurons)


  • Carry instructions from CNS to peripheral effectors via efferent fibers (axons)
• Somatic motor neurons of SNS


  • Innervate skeletal muscles
• Visceral motor neurons of ANS


  • Innervate all other peripheral effectors (smooth and cardiac muscle, glands, adipose tissue)
• Types of neuroglia in the CNS

  • Astrocytes
  • Ependymal cells
  • Oligodendrocytes
  • Microglia
• Astrocytes


  • Maintain blood brain barrier (BBB)
  • Create three-dimensional framework for CNS
  • Repair damaged nervous tissue
  • Guide neuron development
  • Control interstitial environment
• Ependymal cells


  • Form epithelium that lines central canal of spinal cord and ventricles of brain
  • Produce and monitor cerebrospinal fluid (CSF)
  • Have cilia that help circulate CSF
• Oligodendrocytes


  • Cooperate to form a myelin sheath; Myelin insulates myelinated axons; Increases speed of action potentials; Makes nerves appear white
• Microglia


  • Smallest and least numerous neuroglia; Migrate through nervous tissue; Clean up cellular debris, wastes, and pathogens
• Neuroglia of the PNS

  • Satellite cells
  • Schwann cells
• Satellite cells


  • Surround ganglia; Regulate interstitial fluid around neurons
• Schwann cells (neurolemmocytes)


  • Form myelin sheath or indented folds of plasma membrane around axons; A myelinating Schwann cell sheaths only one axon; Many Schwann cells sheath entire axon