Human Brain Mapping - The Neuron Doctrine

The Neuron Doctrine

• Neuron doctrine - A set of carefully constructed elementary set of observations regarding neurons. For more granularity, more current, and more advanced topics, see the cellular level section
• Asserts that neurons fall under the broader cell theory, which postulates:
  • All living organisms are composed of one or more cells.
  • The cell is the basic unit of structure, function, and organization in all organisms.
  • All cells come from preexisting, living cells.
• The Neuron doctrine postulates several elementary aspects of neurons:
  • The brain is made up of individual cells (neurons) that contain specialized features such as dendrites, a cell body, and an axon.
  • Neurons are cells differentiable from other tissues in the body.
  • Neurons differ in size, shape, and structure according to their location or functional specialization.
  • Every neuron has a nucleus, which is the trophic center of the cell (The part which must have access to nutrition). If the cell is divided, only the portion containing the nucleus will survive.
  • Nerve fibers are the result of cell processes and the outgrowths of nerve cells. (Several axons are bound together to form one nerve fibril. see also: Neurofilament. Several nerve fibrils then form one large nerve fiber. Myelin, an electrical insulator, forms around selected axons.
  • Neurons are generated by cell division.
  • Neurons are connected by sites of contact and not via cytoplasmic continuity. (A Cell membrane isolates the inside of the cell from its environment. Neurons do not communicate via direct cytoplasm to cytoplasm contact.)
  • Law of Dynamic Polarization. Although the axon can conduct in both directions, in tissue there is a preferred direction of transmission from cell to cell.
• Elements added later to the initial Neuron doctrine
  • A barrier to transmission exists at the site of contact between two neurons that may permit transmission. (Synapse)
  • Unity of Transmission. If a contact is made between two cells, then that contact can be either excitatory or inhibitory, but will always be of the same type.
  • Dale's Law, each nerve terminal releases a single type of neurotransmitter.
• Some of the basic postulates in the Neuron doctrine have been subsequently questioned, refuted, or updated. See the cellular level section topics for additional information.