Nervous system

• Divisions of the nervous system


  • Central nervous system
  • Peripheral nervous system
• Divisions of the central nervous system

  • Brain
  • Spinal cord
• Brain


  Part of the central nervous system located in the skull
• Spinal cord


  Part of the central nervous system located in the spine
• Divisions of the peripheral nervous system

  • Somatic nervous system
  • Autonomic nervous system
• Somatic nervous system


  Part of the peripheral nervous system that interacts with the external environment
• Components of the somatic nervous system

  • Afferent nerves (carry sensory signals)
  • Efferent nerves (carry motor signals from the central nervous system to skeletal muscles)
• Autonomic nervous system


  Regulates the body's internal environment
• Components of the autonomic nervous system

  • Sympathetic nerves
  • Parasympathetic nerves
• Sympathetic nerves


  Autonomic motor nerves that project from the central nervous system in the lumbar and thoracic regions of the spinal cord, synapse on second-stage neurons at a substantial distance from their target organs
• Parasympathetic nerves


  Autonomic motor nerves that project from the brain and sacral region of the spinal cord, synapse near their target organs on very short second-stage neurons
• Sympathetic nerves


  Stimulate, organize, and mobilize energy resources in threatening situations
• Parasympathetic nerves


  Act to conserve energy
• Autonomic target organs


  Receive opposing sympathetic and parasympathetic input, activity is controlled by relative levels of sympathetic and parasympathetic activity
• Sympathetic changes


  Indicative of psychological arousal
• Parasympathetic changes


  Indicative of psychological relaxation
• Projections of the peripheral nervous system

  • Spinal nerves
  • Cranial nerves
• Components of the cranial nerves

  • Sensory drives
  • Motor fibers
  • Autonomic motor fibers (parasympathetic)
• The nervous system is a "system of twos"
• Meninges


  • Dura mater
  • Arachnoid membrane
  • Subarachnoid space
  • Pia mater
• Cerebrospinal fluid


  Protects the central nervous system, supports and cushions the brain
• Central canal


  Runs the length of the spinal cord
• Cerebral ventricles


  Four large internal chambers of the brain
• Blood-brain barrier


  Mechanism that prevents many toxic substances from passing from the blood to the brain, a consequence of the special structure of cerebral blood vessels
• Cells of the nervous system

  • Neurons
  • Glial cells
• Neuron cell membrane

  Composed of a liquid bilayer or two layers of fat molecules
• Components of the neuron cell membrane

  • Lipid bilayer
  • Protein molecules (channel proteins, signal proteins)
• Types of neurons


  • Multipolar
  • Unipolar
  • Bipolar
  • Interneurons
• Gross neural structures in the nervous system

  • Clusters of cell bodies (nuclei, ganglia)
  • Bundles of axons (tracts, nerves)
• Types of glial cells

  • Oligodendrocytes
  • Schwann cells
  • Microglia
  • Astrocytes
• Oligodendrocytes


  Glial cells that provide multiple myelin segments, increasing the speed and efficiency of axonal conduction
• Schwann cells


  The only glial cells that can guide axonal regeneration after damage
• Microglia


  Smaller glial cells that respond to injury and disease, triggering inflammatory responses
• Astrocytes


  Largest glial cells that make contact with neurons, allow some chemicals to pass from the blood into central nervous system neurons, block other chemicals, exchange chemical signals with neurons and other astrocytes
• Golgi stain


  Used when the overall shape of neurons is of interest
• Nissl stain


  Used to estimate the number of cell bodies in an area
• Electron microscopy


  Provides detailed information about neuronal structure, but can make it difficult to visualize general aspects of neuroanatomical structure
• Neuroanatomical tracing techniques


  • Anterograde (forward tracing)
  • Retrograde (backward tracing)
• Directions in the vertebrate nervous system

  • Anterior
  • Posterior
  • Dorsal
  • Ventral
  • Medial
  • Lateral
• Components of the spinal cord

  • Gray matter (cell bodies, unmyelinated interneurons, dorsal horns, ventral horns)
  • White matter (myelinated axons)