When neuron animations are displayed, there are frequently seen neurons, axons a

Question

When neuron animations are displayed, there are frequently seen neurons, axons arranged in a lattice with a lot of empty space between. I'm interested if there is indeed empty space in the brain, or if it is filled with some sort of fluid? I've checked an article on cerebrospinal fluid but am not sure that it is present all throughout the brain.

The reason I'm asking is that I'm thinking of neurotransmitters- they are released in synapses, but I'm not sure how they stay there - are they suspended in some liquid as well?

Explanation / Answer

Not so empty, actually.

The human brain has a mass of ~1.5kg, and volume ~1200cc (a little bigger for men, a little smaller for women). So is heavier than water by a good margin.

While it has Cerebrospinal fluid, that only occupies the subarachnoid space (the space below the skull and above the cortex, contained between two layers: pia matter and arachnoid membrane) and the ventricular system (several spaces inside the brain, remnants of the embryological development of the brain).

Neuron density may vary widely, depending mainly on the particular characteristics of neuron cell types and their interconnections. But besides neurons, there's a lot of infrastructure inside the brain. For example:

About the last part of your question, the synaptic cleft (the space between pre-synaptic and post-synaptic neurons) is a salty solution: water with high concentration of sodium and chloride ions (and also calcium ions, neurotransmitters and a lot more). These ion concentrations are fundamental to the generation of action potentials, neural signaling, and the general dynamics of the brain.

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