• 100 billion neurons, 10x more glial cells
  • neurons are anatomically independent - come close, but never touch - differ from "regular" cells
    • neurons have "specialized extensions" - dentrites and axons
    • specialized structures - terminal buttons - produce neurotransmitters
    • communicate through electrochemical process
  • communicate across synapses
  • do not heal sponteneously (brain, spinal cord)
  • The nerve impulse usually travels from the dendrites and soma to the branching ends of the axon
  • Different types:
    • Purkinje - spread out, 1000s of dentritic spines, mostly in cortex
    • sensory "interneurons" - connect one neuron to another (reflex)
    • pyramidal - motor neurons - wide branching dentrites, carry information to distant targets
    • bipolar - visual (eye) limited area, short axon


  • Axons covered in myelin sheath - inscrease speed, insulates, white matter
    • myelin formed by glial cells, called oligodentrocytes (CNS) and by Schwann cells (PNS)
    • develops at birth, susceptible to breakdown (MS)
    • buldles of myelinated neurons make up tracts, pathways, or fibers in the CNS and PNS
  • cell bodies are grey - nuclei (CNS) and ganglia (PNS)

  • Glial cells:
    • from Greek gliok: nerve glue
    • offer structural support to neurons
    • physical and chemical buffers between neurons
    • supply nutrients
    • oligodentrocytes (myelin), microglia (scavengers), astrocytes (fill up empty spaces)

      spinal cord injury induces increased expression of the death receptor CD95/Fas by neurons, lymphocytes, microglia

  • Blood-brain Barrier - semi-permeable membrane
    • Protects the brain from "foreign substances" in the blood that may injure the brain.
    • Protects the brain from hormones and neurotransmitters in the rest of the body.
    • Maintains a constant environment for the brain.


    (see here)

  • Synapses
  • More on Action Potential