Nervous Tissue Intro

• Nervous Tissue

  Neurons & Neuroglia

  
• Nervous System Functions

  • Receive & transmit information
  • Process information
  • Respond to information

  
• Divisions of Nervous System

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

  
• Central nervous system (CNS)

  • Brain and spinal cord
  • Processes & integrates information

  
• Peripheral nervous system (PNS)

  • All other parts of the nervous system that branch off of CNS
  • Connects CNS to rest of body

  
• PNS Divisions

  • Sensory (afferent)
  • Motor (efferent)

  
• Sensory (afferent) PNS

  • Somatic – consciously perceived from receptors in skin, muscles, bones, joints
  • Visceral – unconsciously perceived from receptors in viscera (e.g., heart, stomach, bladder)

  
• Motor (efferent) PNS

  • Somatic – controls skeletal muscles (voluntary)
  • Visceral (AKA autonomic nervous system) – control involuntary muscles, glands
• Autonomic Nervous System Divisions

  • Sympathetic ("fight or flight")
  • Parasympathetic ("rest & digest")

  
• Neurons

  • Primary/functional cells of the nervous system
  • Receive, process, respond

  
• Neuroglia


  • Supportive cells of the nervous system
  • Aka "glial cells" or "glia"
  • Provide support to neurons

  
• Neuron Structure

  • Soma (cell body)
  • Dendrites
  • Axon

  
• Functional Classes of Neurons

  • Sensory (afferent) neurons (PNS)
  • Interneurons (CNS)
  • Motor (efferent) neurons (PNS)

  
• CNS Glia

  • Astrocytes
  • Oligodendrocytes
  • Ependymal Cells
  • Microglia

  
• PNS Glia

  • Satellite Cells
  • Schwann Cells
• Myelin Sheath

  • Spiral layers (up to 100 layers) of plasma membranes wrapped around nerve fibers
  • Increases conduction speed in axon
  • Improves regeneration of damaged axons
• Myelination

  • Production of myelin sheath
  • Begins @ 14 weeks of fetal development, rapid production during infancy, complete in late adolescence
  • Dietary fat necessary
• Schwann cells


  Entire cell body wrapped around 1 axon
• Oligodendrocyte


  • Cell body does not wrap around axon
  • 1 oligodendrocyte myelinates many nerve fibers
• Saltatory conduction

  • Faster propagation in myelinated axons
  • Myelin prevents Na+ leakage between nodes
  • Na+ diffuses along axon between nodes (where covered w/ myelin)
  • No new AP generation required in between nodes
• CNS fibers do not regenerate
• Nerve fiber (axon) regeneration in the PNS can occur if the neurosoma is intact and some myelin/Schwann cell remains