Equilibrium Potentials II Answer 5

• The sum of particles on the inside of the squid giant axon is $400\ \text{mOsm} + 50\ \text{mOsm} + 52\ \text{mOsm} + 385\ \text{mOsm} = 887\ \text{mOsm}$.
• The sum of the particles outside of the squid giant axon is $20\ \text{mOsm} + 440\ \text{mOsm} + 560\ \text{mOsm} = 1020\ \text{mOsm}$.
• The difference is 133 mOsm, which is a very large amount!
• If these were the only particles, water would leave the axon because it is more concentrated on the inside (where the number of particles is smaller); thus, the neuron would shrink.
• However, there are other ions that are not in this list, such as magnesium and calcium, that are also important for osmotic balance, as well as impermeable particles on either side that contribute to allowing the axon to remain in osmotic balance.