How does the nervous system change as it ages?
Face facts! If you are over 20, you probably have two miles less wiring in your brain than this time yesterday. If you had a few drinks last night it may be less still. Luckily, you were born with around 100 billion nerve cells (neurons) so at first you can afford these losses. The nervous system compensates by sprouting new connections from surviving neurons. Surviving motor neurons in our spinal cord, for example, more than double in size so that when some are lost during ageing we can still control our muscles.
Our brains function differently as we start to use different pathways. Our ability to learn might reduce, but we already know more than we used to. However, somewhere around late middle age there is a small, but detectable decrease in cognitive ability, and if we are unlucky enough to develop a neurodegenerative disorder such as Alzheimer’s disease or motor neuron disease, we find that normal ageing has reduced our ability to compensate just when we need it most. This is one reason why normal ageing is the biggest single risk factor for most neurodegenerative disorders.