L2 - Cells of the NS

• The directional terms used to describe structures locations in relation to each other change depending on if you are above or below the diencephalon
• Secondary brain vesicles and their adult equivalent

  • telencephalon - cerebrum
  • diencephalon - diencephalon (thalamus, hypothalamus, epithalamus)
  • mesencephalon - brain stem: midbrain
  • metencephalon - brain stem: pons & cerebellum
  • myelencephalon - brain stem: medulla oblongata
• Cerebrospinal fluid is derived from blood
• The original single central canal undergoes complex changes with growth of the brain and become

  lateral ventricles (ventricles 1 & 2) in each hemisphere

  third ventricle in the diencephalon that joins the lateral ventricles together by a foramen

  forth ventricle above the pons and medulla and below the cerebellum that joins to the third ventricle via cerebral aqueduct

  the spinal canal
• Cerebrospinal fluid is made in the ventricles and flows out to the fluid filled space around the brain through apertures in the region of the brain stem. The CSF can leave the ventricles and go into the subarachnoid space
• Label the ventricles in the brain

  A) lateral ventricles

  B) third ventricle

  C) lateral aperture

  D) fourth ventricle

  E) central canal

  
• The basal plate neurons become restricted to motor neurons located in the ventral and lateral horns of the spinal cord. The alar plate neurons form the remainder of the spinal cord including the dorsal horn
• In the medulla oblongata, the basal plate neurons form motor nuclei in the medulla near the midline. The alar plate neurons form sensory nuclei in the dorsal part of the medulla and a larger structure in the ventral part of the medulla

  
• In the adult midbrain, the basal plate neurons form a few motor nuclei near the midline while the alar plate neurons form large nuclei in the remainder of the midbrain

  
• The thalamus is a relay station that takes in incoming sensory information, relays that info to the cerebral cortex. It only contains interneurons
• In the embryonic diencephalon it only contains alar plate. Therefore it splits into a dorsal alar plate and a basal alar plate. The basal alar plate forms the hypothalamus and the dorsal alar plate forms the thalamus
• Neuroglial cells consist of

  astrocytes

  oligodendrocytes

  ependymal cells

  Schwann cells

  satellite cells

  microglia***
• Neuroglial cells are derived from neuroepithelial cells or neural crest cells
• The three structural classifications of neurons are

  multipolar - many projections coming off of the cell (purkinje cell & pyramidal cell)

  bipolar -2 projections branching off (olfactory cell & retinal cell)

  unipolar/pseudounipolar (dorsal root ganglion cell)
• The most functional type of neuron is the interneuron which makes up 99.98% of the all the neurons in the body
• Functional classifications of neurons

  sensory (afferent) neurons

  motor (efferent) neurons

  interneurons
• Interneurons are the connections between sensory and motor neurons. They are all located in the CNS
• Microglia are derived from mesoderm. They are monocyte derived cells that differentiate into macrophage. They become activated in response to injury or disease. They are phagocytic cells that will engulf debris
• Astrocytes are the most abundant glial cell. They contain cell processes called end feet that cover neurons (to provide metabolic support), all blood vessels in the CNS (maintain the blood-brain barrier), and inner surface of pia mater.
• Ependymal cells line the ventricular system and central canal of the spinal cord. They produce and circulate CSF with the help of their cilia and microvilli on the apical surface
• Oligodendrocytes produce the myelin sheath for neurons in the CNS. They contain cellular processes that wrap around the axons of neurons. 1 oligodendrocyte can myelinate many axons
• Schwann cells are derived from neural crest cells. They form the myelin sheath for neurons in the PNS. 1 schwann cell can only myelinate 1 axon. Non-myelinated axons are still surrounded by schwann cells but not wrapped in myelin
• Satellite cells surround cell bodies in the PNS and are found in ganglia. They are derived from neural crest cells. They have a metabolic and structural function (support for neurons)