nerves (noun) are a group of long thin fibres that carry information or instructions between the brain and other parts of the body. A nerve is like an electric cable that passes electric current. When your hand touches a something hot, the hand sends the feeling to the brain through nerves.
You don't have to be a doctor to use the word nerve because it is used in a few natural English expressions you should know.
The word nerves can be used to describe worry, nervousness or anxiety about something that is going to happen:
"I always suffer from nerves when I have to make a speech in front of lots of people."
"Have a drink of whiskey to calm your nerves before you make your speech."
This idiom is used to show you are nervous about something:
"I was a bundle of nerves before my big job interview."
"I'm a bag of nerves today - I don't know what's wrong with me!"
When we annoy somebody a lot we get on their nerves.
"We really started to get on each others nerves when we lived in that small apartment together."
"Can you hear that banging sound? It's really getting on my nerves!"
To be very brave. When you have nerves of steel your are fearless and have courage:
"I think all firefighters have nerves of steel."
"You need nerves of steel to be an Formula 1 racing driver."
To make someone unhappy or upset by saying something to the person doesn't like.
"I think I hit a nerve when I mentioned she was getting fat. I wish I'd hadn't said anything."
"She looked really upset when you talked about her 40th birthday. You really touched a nerve when you discussed her age."
When you lose your nerve you become too scared to do something.
"I was going to try bungee jumping but I lost my nerve a didn't do it."
"Don't lose your nerve now - you promised to come on the roller-coaster with me."
When someone has a lot of nerve they show great rudeness; a lot of audacity or brashness. The expression "What a nerve!" is also used.
"You took my seat! You have a lot of nerve sitting there!"
"Did you hear what he said to her. What a nerve! I'm not surprised that she hit him!"
Now use your amazing brains to complete these expressions.
Link: 10 idioms to describe feeling good and bad