Brain and nerves

About this course

In 1873 the Italian physician Camillo Golgi, working in a makeshift lab in a kitchen, found a silver stain that colours a few nerve cells completely black against a clear background. Golgi believed the nervous system was one continuous network. The Spanish histologist Santiago Ramón y Cajal used the same stain to argue the opposite: each neuron is a separate cell, and cells meet without fusing. Cajal won over leading anatomists at a meeting in Berlin in 1889. In 1906 the two men shared the Nobel Prize, and Golgi used his own lecture to criticise Cajal's idea.

The seven units begin with a map of the nervous system, where twelve pairs of nerves leave the brain and 31 pairs leave the spinal cord. Neurons and glial cells follow: an adult brain holds about 86 billion neurons, each with one axon. How nerve signals travel shows an action potential swinging the inside of a neuron from −70 mV to +30 mV and back in about 2 milliseconds. Parts of the brain notes that the brain is about 2% of body weight but uses about 20% of the oxygen. In senses and movement, most fibres that move your right hand start in the left brain and cross in the medulla. The reflex unit shows a knee jerk with no brain in the loop. The 3D brain lets you tap a part to read its job, fire a neuron with Stimulate, and follow a synapse and a reflex arc step by step.

Paul Broca's 1861 patient, Louis Victor Leborgne, could say only one syllable, Tan. Damage in the left frontal region, now called Broca's area, became early evidence that particular jobs live in particular parts of the cortex.