Complete the following paragraph. The spinal cord is a column of _____ that extends through the _____. The spinal cord and brain make up the _____. The _____ regions have enlargements, which give rise to the nerves serving the _____, respectively. The inferior tip of the spinal cord is called the _____. It is located just below the level of L1. There are _____ pairs of spinal nerves, which come from the merging of the _____. All spinal nerves are classified as mixed nerves because they contain both _____.