Question

how you ranked the treatments:

1. isotonic saline 2. hypertonic saline 3. hypotonic saline

you have chosen isotonic saline. predict the effects of your treatment on the following:
blood sodium concentration 114 (low) decrease no change increase
brain matrix pressure 27 (high) decrease no change increase
neuron firing rate 4.5 (high) decrease no change increase
net free water movement out of vessel initial value into vessel in equilibrium out of vessel
justify your answer for net free water movement.

Explanation:

Step1: Understand isotonic saline

Isotonic saline has the same osmolarity as blood plasma.

Step2: Analyze blood sodium concentration

Since it is isotonic, it won't change the sodium - water balance in a way that affects blood sodium concentration. So, no change.

Step3: Analyze brain matrix pressure

As it doesn't cause significant fluid shifts into or out of cells, it will not change brain matrix pressure. So, no change.

Step4: Analyze neuron firing rate

No major changes in ion concentrations or fluid balance that would directly affect neuron firing rate occur with isotonic saline. So, no change.

Step5: Analyze net free water movement

Isotonic solutions do not create an osmotic gradient for net water movement across cell membranes or vessel walls. So, in equilibrium.

Answer:

Blood Sodium Concentration: No Change
Brain Matrix Pressure: No Change
Neuron Firing Rate: No Change
Net Free Water Movement: In Equilibrium