What does the spinal needle in a lumbar puncture reach to collect CSF?

The spinal needle in a lumbar puncture is specifically designed to reach the subarachnoid space in order to collect cerebrospinal fluid (CSF). The subarachnoid space is the area between the arachnoid membrane and the pia mater, which houses the CSF that cushions the spinal cord and brain. During the procedure, the needle is inserted into the lower back, typically between the L3-L4 or L4-L5 vertebrae, to ensure that it enters this space safely, avoiding any injury to the spinal cord.

The purpose of collecting CSF from the subarachnoid space can include diagnosing conditions such as infections, bleeding, or multiple sclerosis, and it is crucial that the needle reaches this specific area to obtain an accurate sample for analysis. The other options, while related to spinal anatomy, do not contain CSF or are not the target location for collecting CSF in a lumbar puncture.