system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can doctors reattach the nerves in limbs but they cannot reattach a broken spinal cord?
gpt
Simply because there are way too many nerves to connect in a spinal cord and it is difficult to see which nerve connects wo which. 31 nerve pairs, all compacted in the space of a few centimeters, compared to 10, all spaced out, there is no margin for error, so doctors leave nerve connections.

Take it like this. You're friend is holding 20 sticks and you can only see the middle, not the ends. Your friend then breaks all 20 sticks and, without looking at the ends, you have to connect them all together again. It's time consuming, hard and expensive.