Neuron Doctrine 1891 – Our Body’s Signalling Network

According to neurobiologist Gordon Shepherd, the Neuron Doctrine is one of the great ideas of modern thought, equal in importance to quantum theory and relativity in physics, or the periodic table and chemical bonding in chemistry.

Arising from microscopic studies in the late 1800s, the Neuron Doctrine proposes that cells called neurons act as the functional signalling units of the nervous system and connect to one another in several precise ways. 

The doctrine was formally stated in 1891 by German anatomist Wilhelm von Waldeyer-Hartz, based on observations by Spanish neurologist Santiago Cajal, Italian pathologist Camillo Golgi and other scientists. Cajal improved Golgi's special silver stains, helping make details of cellular branching processes more visible under the microscope.

Although modern scientists have modified the original version of the Neuron Doctrine, they agree that most neurons have the following components:

• Dendrites: Branch-like structures that carry electrochemical signals from other neurons to the cell body, or soma.
• Soma: Also known as the cell body.
• Axon: A structure that carries signals away from the cell and can extend up to 1 metre.

In many cases, signals pass from one neuron to another through neurotransmitter chemicals released from a neuron's axon. They travel across a small connection area, the chemical synapse, then enter a neighbouring neuron's dendrite. If the net stimulation of signals reaching the neuron is large enough, it produces a brief electrical impulse called an action potential, which travels along the axon. Cellular passage channels also create direct connections between neurons.

Sensory neurons carry signals from sensory receptor cells in the body to the brain, while motor neurons carry signals from the brain to muscles. Glial cells, more numerous than neurons in the brain, provide structural and metabolic support to neurons. 

Although neurons are generally not reproduced in adults, new connections between neurons can form throughout life. Each of the 100 billion neurons may have thousands of synaptic connections. 

• Multiple sclerosis (MS) results from insufficient myelin (chemical insulation) around axons. 
• Parkinson’s disease is associated with a deficiency of the neurotransmitter dopamine, normally produced by certain neurons in the midbrain.

Image description: Ramón y Cajal’s illustration of chick cerebellar cells from Estructura de los centros nerviosos de las aves (Structure of the Nervous Centres of Birds), Madrid, 1905.

Description of the article image: A neuron with multiple dendrites, a cell body and a long axon. The capsule-like protrusions on the axon are myelin sheath cells.

Historical figures mentioned in the article: Heinrich Wilhelm Gottfried von Waldeyer-Hartz (1836–1921), Camillo Golgi (1843–1926), Santiago Ramón y Cajal (1852–1934)

• Previous topic: Surgical Gloves 1890 – A Step Towards Preventing Infection
• Next topic: Discovery of Viruses 1892 – Living Microbes