 We're going to discuss the external features of the spinal cord in this video. So it lies in the vertebral canal of the vertebral column, which provides support and protection. The cord is continuous with the medulla oblongata, the lowest section of the brainstem. The spinal cord is covered by three thin membranous layers known as meninges. That's the pier, arachnoid and dura marta from inside to out. Between the pier and arachnoid marta lies the subarachnoid space, which contains cerebrospinal fluid. Between the arachnoid and dura is the subdural space, but this is just a potential space. There's nothing actually in here. Marta means mother in Latin, pier means tender. The tender mother sticks close to its baby the spinal cord. Dura, on the other hand, means tough and the tough mother is separated to a degree from her baby. Between the dura marta and the surrounding bone is the epidural space, which is filled with epidural fat. And these spaces and their sheaths continue cordially down to the level of the second sacral vertebra. The spinal cord is divided into segments and these segments relate to spinal nerves. There are eight cervical segments known as C1 to C8, 12 thoracic, T1 to T12, 5 lumbar, L1 to L5, 5 sacral, S1 to S5, and then one coxigil. It is roughly cylindrical in shape, but enlarges in two areas. The cervical enlargement consists of the spinal cord segments C5 to T1 and provides innovation to the upper limb via the brachial plexus. It corresponds to vertebra C3 to T1. The lumbar enlargement consists of spinal cord segments L1 to S3 and innovates the lower limb via the lumbo sacral plexus. It corresponds to vertebra T9 to L1 and much of these lower nerve roots make up the quarter equina. Or horse's tail. We'll make our way through these layers again to have a closer look at that. So there it is there, the quarter equina, the constituents of which head out, lumbar vertebrae, down to the sacrum and down to the coccyx as well. The spinal cord proper thins around L1 into the conus medularis. At the very tip of this structure, we can see the phylum terminale, which extends quarterly to attach to the first coxigil vertebra. Let's revise some embryology now. Remember the spinal cord occupies the entire length of the vertebral canal up until the third month of life. Thereafter the vertebral column elongates faster than the spinal cord and at birth the cord terminates at L3. By the time you're an adult your spinal cord terminates between L1 and L2. So why is this important? Because when doctors are performing a lumbar puncture or an epidural they need to access the subarachnoid space or the epidural space. But they do not want to put their needle through the spinal cord. So these procedures are performed below L3 in children and below L1 and L2 in adults. Click the link in the video description to navigate around this model yourself. Hit subscribe if you liked this video. Thanks for watching and we will see you next time.