Question

the neuronal tissue of the brain is very sensitive, so it needs a safe, stable environment in which to function. therefore, the brain has a number of protective barriers including the blood - brain barrier. other protective barriers are the cerebrospinal fluid, the meninges (membranes), and the cranial bones.
as its name suggests, the blood - brain barrier (bbb) prevents harmful substances from entering the brain from the blood. this barrier not only protects the brain from blood - borne infections, it also protects the brain from the normal fluctuations of solutes in the extracellular environment. solutes are substances that are soluble in the bloodstream (this means they are hydrophilic). the brain is protected from some amino acids and ions +.
why is it important for the brain to have constant concentrations of ions and amino acids?
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Explanation:

Neurons in the brain communicate via electrical signals. These signals rely on specific ion gradients (like sodium, potassium, calcium ions). A constant concentration of ions ensures proper generation and propagation of action potentials. Amino acids are important for neurotransmitter synthesis (e.g., glutamate is an amino - acid neurotransmitter). Fluctuations in amino - acid levels could disrupt neurotransmitter production and synaptic transmission. Also, neurons are sensitive cells, and maintaining a stable internal environment (homeostasis) of ions and amino acids is crucial for their survival and proper functioning, as any significant change could lead to cell damage or dysfunction.

Answer:

Constant concentrations of ions are necessary for the generation and propagation of action potentials (electrical signals in neurons). Amino acids are important for neurotransmitter synthesis. Fluctuations in their levels could disrupt neurotransmission and neuron function. Also, neurons are sensitive cells, and maintaining stable concentrations helps in their survival and proper operation (homeostasis).