A lumbar puncture is performed by inserting a fine needle between the third and fourth lumbar vertebrae and withdrawing a sample of cerebrospinal fluid from the subarachnoid space. (For clarity, spinal nerves are not shown.)
Third lumbar vertebra
Because cerebrospinal fluid occupies the subarachnoid space of the meninges, it completely surrounds the brain and spinal cord. In effect, these organs float in the fluid. The CSF protects them by absorbing forces that might otherwise jar and damage their delicate tissues.
H Where are the ventricles of the brain located?
^9 How does cerebrospinal fluid form?
^9 Describe the pattern of cerebrospinal fluid circulation.
The terms nerve fiber and axon are used synonymously. In chapters 9 and 10 care was taken to distinguish between the term nerve fiber, which is part of a nerve cell, and muscle fiber, which refers to the entire muscle cell. Because the term nerve fiber is commonly used, in the remaining text nerve fiber will be reintroduced and used synonomously with axon.
130 millimeters of water (10 millimeters of mercury). At the same time, samples of CSF may be withdrawn and tested for the presence of abnormal constituents. Red blood cells in the CSF, for example, may indicate a hemorrhage in the central nervous system.
A temporary drain inserted into the subarachnoid space between the fourth and fifth lumbar vertebrae can relieve pressure. In a fetus or infant whose cranial sutures have not yet united, increasing intracranial pressure (ICP) may cause an enlargement of the cranium called hydrocephalus, or "water on the brain." A shunt to relieve hydrocephalus drains fluid away from the cranial cavity and into the digestive tract, where it is either reabsorbed into the blood or excreted (fig. 11B). ■
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.