Ch 12

• Nervous Tissue


  3% of body mass, cellular, 20% extracellular space
• Types of cells in nervous tissue


  • Neurons
  • Neuroglia / glial cells
• Neurons


  Conduct nervous impulses
• Neuroglia / glial cells


  Supporting cells, "nerve glue"
• Divisions of the Nervous System


  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
• Central Nervous System (CNS)


  • Spinal cord, brain
  • Integrate, process, coordinate sensory input and motor output
• Peripheral Nervous System (PNS)


  • All neural tissue outside CNS
  • Carry info to/from CNS via nerves
• Divisions of the PNS


  • Sensory/Afferent Division
  • Motor Efferent Division
• Sensory/Afferent Division


  • Somatic afferent division
  • Visceral afferent division
• Somatic afferent division


  From skin, skeletal muscles, joints
• Visceral afferent division


  From internal organs
• Motor Efferent Division


  • Somatic Nervous System
  • Autonomic Nervous System (ANS)
• Somatic Nervous System


  "Voluntary nervous system", to 40 skeletal muscles
• Autonomic Nervous System (ANS)


  • Sympathetic Division
  • Parasympathetic Division
• Sympathetic Division


  "Fight or flight"
• Parasympathetic Division


  "Rest and digest", tend to be antagonistic to Sympathetic Division
• Neuron


  • Extreme longevity
  • Amitotic (exceptions: hippocampus, olfactory receptors)
  • High metabolic rate: need O, and glucose
• Nervous System


  Nervous Tissue

  
• 3% of body mass
• Cellular


  ~20% extracellular space
• Two categories of cells


  • Neurons: conduct nervous impulses
  • Neuroglia / glial cells: "nerve glue", supporting cells

  
• Central Nervous System (CNS)


  • Spinal cord, brain
  • Function: integrate, process, coordinate sensory input and motor output

  
• Peripheral Nervous System (PNS)


  • All neural tissue outside CNS
  • Function: carry info to/from CNS via nerves

  
• Nerve


  Bundle of axons (nerve fibers) with blood vessels and CT
• Divisions of PNS


  • Sensory/Afferent Division
  • Motor/Efferent Division
• Somatic afferent division


  From skin, skeletal muscles, joints
• Visceral afferent division


  From internal organs
• Somatic Nervous System


  • "Voluntary nervous system"
  • To skeletal muscles
• Autonomic Nervous System (ANS)


  • "Involuntary nervous system"
  • To smooth & cardiac muscle, glands
• Sympathetic Division


  "Fight or flight"
• Parasympathetic Division


  "Rest and digest"
• Neuron


  Function: conduct nervous impulses (message)

  
• Neuron characteristics


  • Extreme longevity
  • Amitotic (exceptions: hippocampus, olfactory receptors)
  • High metabolic rate: need O2 and glucose
• Nucleus


  Large, large nucleolus (rRNA)
• Mitochondria, ribosomes, RER, Golgi


  Many (for ATP, protein synthesis to produce neurotransmitters)
• Nissl bodies


  Visible RER & ribosomes, gray
• Neurofibrils


  Neurofibrils = neurofibrils, neurotubules (internal structure)

  
• Two types of processes (cell extensions)


  • Dendrites: receive info, carry a graded potential toward soma, contain same organelles as soma, short, branched, end in dendritic spines
  • Axon: single, long, carry an action potential away from soma, release neurotransmitters at end to signal next cell, long ones = "nerve fibers", contains: neurofibrils & neurotubules (abundant), vesicles of neurotransmitter, lysosomes, mitochondria, enzymes, no Nissl bodies, no Golgi (no protein synthesis in axon), connects to soma at axon hillock, covered in axolemma (membrane), may branch: axon collaterals, end in synaptic terminals or knobs, may have myelin sheath: protein+lipid (protection, insulation, increase speed of impulse)
• Axoplasmic transport


  • Move materials between soma and terminal along neurotubules on kinesins
  • Anterograde transport = soma → terminal (neurotransmitters from soma)
  • Retrograde transport = terminal → soma (recycle breakdown products from used neurotransmitters)
• Some viruses use retrograde transport to gain access to CNS (Polio, Herpes, Rabies)