Final answer:
Therefore, the correct answer to the question is option 1) It shrinks.
A brain cell exposed to a hypertonic solution will shrink due to water moving out of the cell to the external environment in an attempt to balance solute concentrations, a process called crenation.
Step-by-step explanation:
When the concentration of solutes gets too high in our blood, it creates a hypertonic environment for our cells. In such a hypertonic solution, the net flow of water will be out of a cell due to osmosis because the external environment has a higher solute concentration compared to the inside of the cell. The result is that the cell will shrink, or crenate, due to the loss of water. This process makes the cytosol denser, impacting diffusion in the cell and potentially impairing its function or even causing cell death. Figure 41.2 and related text describe that cells in a hypertonic environment tend to shrink, while in a hypotonic environment, they swell.
For a brain cell with a 95% hypertonic environment compared to its internal environment, the expected outcome would be that the brain cell shrinks due to water moving out of the cell and into the blood to balance the solute concentrations. This is true for all cells, including red blood cells that also crenate under similar hypertonic conditions as explained in various figures and accompanying explanations.